Resorting Query Results for 2005AJ....129.1237C

TY - Journal T1 - Southern stars that can be used as unpolarized standards A1 - Gil-Hutton, R. A1 - Benavidez, P. JO - Monthly Notices of the Royal Astronomical Society VL - 345 Y1 - 2003/10/1 SP - 97 EP - 99 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.345...97G&db_key=AST&high=42a068d47529854 N2 - Results are presented from a programme of linear polarimetry to find unpolarized stars in the solar vicinity that could be used as standard stars and are within reach of telescopes in the southern hemisphere. We find up to 10 suitable candidates. On the other hand, among the observed stars, HD 112164, HD 114613, HD 130307 and HD 160691 are objects within 27 pc of the Sun but showed a relatively high polarization in the ~0.1 per cent level, which must be of intrinsic origin. ER - TY - Journal T1 - Photometry of Fourteen Main Belt Asteroids A1 - Gil-Hutton, R. A1 - Cañada, M. JO - Revista Mexicana de Astronomia y Astrofisica VL - 39 Y1 - 2003/4/1 SP - 69 EP - 76 KW - Minor planets/ asteroids UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003RMxAA..39...69G&db_key=AST&high=42a068d47529854 N2 - The results of CCD photometry of 14 main belt asteroids obtained between 1996 and 2000 are presented. For most of them, the V or R composite lightcurves and the values of the synodic rotational period are derived. There exists no previous determination of the period for 11 of the observed objects. ER - TY - Journal T1 - Color diversity among Kuiper belt objects: The collisional resurfacing model revisited A1 - Gil-Hutton, R. JO - Planetary and Space Science VL - 50 Y1 - 2002/1/1 SP - 57 EP - 62 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002P%26SS...50...57G&db_key=AST&high=42a068d47529854 N2 - A re-evaluation of the collisional resurfacing model based on up-to-date Kuiper belt objects size distribution and a more precise treatment of the cosmic-ray environment at the outer Solar System is presented. The result of the irradiation due to cosmic-rays with different energies altered in a different way the material of the objects, producing, under certain conditions, a thick irradiation mantle. Since the collisional resurfacing model is based in the competition between darkening by cosmic-rays and resurfacing due to impacts, the color of objects in different regions of the belt could vary if the projectile populations in those regions are truncated at a different radius. ER - TY - Journal T1 - VR Photometry of Sixteen Kuiper Belt Objects A1 - Gil-Hutton, R. A1 - Licandro, Javier JO - Icarus VL - 152 Y1 - 2001/8/1 SP - 246 EP - 250 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001Icar..152..246G&db_key=AST&high=42a068d47529854 N2 - We present V and R photometry of 16 Kuiper belt objects (KBOs) from the 3.6-m Telescopio Nazionale Galileo and the Complejo Astronómico El Leoncito 2.1-m telescope. We find a wide dispersion in the (V-R) colors of the objects, indicating nonuniform surface properties. If we assume near constant albedos, there does not appear to be a general trend of redness with size, but the color range for classical KBOs in our sample appears to be wider than for Plutinos. Unless the albedo value is variable for different objects, 1998 SN₁₆₅ becomes the largest Plutino so far identified, apart from Pluto (diameter=2400 km) and Charon (1200 km). ER - TY - Journal T1 - Collisional evolution of the outer asteroid belt A1 - Gil-Hutton, Ricardo A1 - Brunini, Adrián JO - Icarus VL - 145 Y1 - 2000/6/1 SP - 382 EP - 390 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000Icar..145..382G&db_key=AST&high=42a068d47529854 N2 - Not Available ER - TY - Journal T1 - Collisional rates and impact velocities of short-period comets with interplanetary particles A1 - Gil-Hutton, R. JO - Planetary and Space Science VL - 48 Y1 - 2000/5/1 SP - 545 EP - 551 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000P%26SS...48..545G&db_key=AST&high=42a068d47529854 N2 - Distributions of collision velocities between short-period comets and particles in the asteroid belt are computed for a sample of 159 objects. For every comet, the mean intrinsic collision probability and the mean collision velocity were obtained. The mean values for the complete sample are i>=1.51×10^-18 km² year^-1 and col>=10.86 km s^-1, and the results for the observable and lost comet samples are: i>=1.45×10^-18 km^-2 year^-1, col>=10.45 km s^-1, and i>=1.88×10^-18 km^-2 year^-1, col>=12.78 km s^-1, respectively. The results obtained show that the collisions occur over a wide and asymmetric range of velocities, and the distributions for individual objects are completely different from each other and often contain fine structure, irregularities and spikes ER - TY - Journal T1 - Collisional evolution of the early asteroid belt A1 - Gil-Hutton, R. A1 - Brunini, A. JO - Planetary and Space Science VL - 47 Y1 - 1999/4/1 SP - 331 EP - 338 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999P%26SS...47..331G&db_key=AST&high=42a068d47529854 N2 - We present numerical results obtained by a simulation of the collisional process between asteroids and scattered comets from the Uranus-Neptune zone. This mechanism allows the use of single exponent incremental size distributions for the initial belt reaching a final distribution that matches the observed population very well. Since the cometary bombardment was extremely efficient removing mass from the primordial asteroid belt in a very short time, we always obtained belts with total masses less than 0.001 M_âŠ• after ~ 2×10⁷ yrs. This result allows processes with an important initial mass preserving Vestas basaltic crust. ER - TY - Journal T1 - Photometry of Asteroids 558 Carmen, 613 Ginevra, and 1124 Stroobantia A1 - Gil-Hutton, Ricardo JO - Revista Mexicana de Astronomia y Astrofisica VL - 34 Y1 - 1998/4/1 SP - 9 KW - PHOTOMETRY/ ASTEROIDS/ OBSERVATION/ CCD CAMERAS/ ROTATION/ TIME FUNCTIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998RMxAA..34....9G&db_key=AST&high=42a068d47529854 N2 - CCD photometry of asteroids 558, 613 and 1124 are herein presented, which was obtained during four observing periods on 1993 and 1995. We have determined the following synodic rotational periods: 558 Carmen (9.264 +/- 0.005 hours), 613 Gineva (16.45 +/- 0.01 hours) and 1124 Stroobantia (16.39 +/- 0.01 hours). ER - TY - Journal T1 - The number of objects in the original asteroid belt A1 - Gil-Hutton, R. JO - Planetary and Space Science VL - 45 Y1 - 1997/2/1 SP - 229 EP - 233 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997P%26SS...45..229G&db_key=AST&high=42a068d47529854 N2 - Using the limited collisional evolution of Ceres and Vesta as constraints for the number of objects in the asteroid belt it is found that a moderate mass depletion by a factor of 3.6 occurred after the end of the accretion period. To model the angular momentum evolution a ``particle-in-a-box'' method is used which takes into account the size distribution of the actual belt and the loss of angular momentum by ejecta escaping preferentially in the prograde direction. It also provides a value of 0.26 for the fraction of leftover impact energy available for further mechanical work after a collision, which is higher than the values used by other authors for simulations. In a belt with these properties the survival during the Solar System age for objects with the dimensions of Vesta is granted, but for asteroids ~ 300 km in diameter the survival probability is a strong function of the region where the object moves. ER - TY - Journal T1 - A Search Program for Objects in the Vicinity of the Earth A1 - Hutton, R. Gil JO - Earth Moon and Planets VL - 71 Y1 - 1995/12/1 SP - 207 EP - 210 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995EM%26P...71..207H&db_key=AST&high=42a068d47529854 N2 - Not Available ER - TY - Journal T1 - Research Note: Photometry of Asteroids 359 Georgia and 789 Lena A1 - Gil-Hutton, R. JO - Revista Mexicana de Astronomia y Astrofisica VL - 31 Y1 - 1995/10/1 SP - 143 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995RMxAA..31..143G&db_key=AST&high=42a068d47529854 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995RMxAA..31..143G&db_key=AST ER - TY - Journal T1 - Pole coordinates of the asteroid 338 Budrosa: implication for the asteroidal family 124 A1 - Hutton, R. Gil A1 - Licandro, J. A1 - Gallardo, T. JO - Planetary and Space Science VL - 43 Y1 - 1995/6/1 SP - 797 EP - 800 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995P%26SS...43..797H&db_key=AST&high=42a068d47529854 N2 - Not Available ER - TY - Journal T1 - Photoelectric Photometry of Asteroids 184 Dejopeja, 498 Tokio and 690 Wratislavia A1 - Gil-Hutton, R. JO - Revista Mexicana de Astronomia y Astrofisica VL - 31 Y1 - 1995/4/1 SP - 19 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995RMxAA..31...19G&db_key=AST&high=42a068d47529854 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995RMxAA..31...19G&db_key=AST ER - TY - Journal T1 - Simulations of Galaxy Formation in a Lambda Cold Dark Matter Universe. II. The Fine Structure of Simulated Galactic Disks A1 - Abadi, Mario G. A1 - Navarro, Julio F. A1 - Steinmetz, Matthias A1 - Eke, Vincent R. JO - Astrophysical Journal VL - 597 Y1 - 2003/11/1 SP - 21 EP - 34 KW - Cosmology: Dark Matter/ Galaxies: Evolution/ Galaxies: Formation/ Galaxies: Structure/ Methods: Numerical UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...597...21A&db_key=AST&high=42a068d47524243 N2 - We present a detailed analysis of the disk component of a simulated galaxy formed in the LambdaCDM cosmogony. At redshift z=0, two distinct dynamical components are easily identified solely on the basis of the orbital parameters of stars in the galaxy: a slowly rotating, centrally concentrated spheroid and a disklike component largely supported by rotation. The disk may be further decomposed into a thin, dynamically cold component with stars on nearly circular orbits and a hotter, thicker component with orbital parameters transitional between the thin disk and the spheroid. Supporting evidence for the presence of distinct thick- and thin-disk components is provided, as in the Milky Way, by the double-exponential vertical structure of the disk and in abrupt changes in the vertical velocity distribution as a function of stellar age. The dynamical origin of these components offers intriguing clues to the assembly of spheroids and disks in the Milky Way and other spiral galaxies. The spheroid is old and has essentially no stars younger than the time elapsed since the last major accretion event, ~8 Gyr ago for the system we consider here. The majority of thin-disk stars, on the other hand, form after the merging activity is over, although a significant fraction (~15%) of thin-disk stars are old enough to predate the last major merger event. This unexpected population of old-disk stars consists mainly of the tidal debris of satellites whose orbital plane was coincident with the disk and whose orbits were circularized by dynamical friction prior to full disruption. More than half of the stars in the thick disk share this origin, part of a trend that becomes more pronounced with age: 9 out of 10 stars presently in the old (age of >~10 Gyr) disk component were actually brought into the disk by satellites. By contrast, only one in two stars belonging to the old spheroid are tidal debris; the rest may be traced to a major merger event that dispersed the luminous progenitor at z~1.5 and seeded the formation of the spheroid. Our results highlight the role of satellite accretion events in shaping the disk, as well as the spheroidal, component and reveal some of the clues to the assembly process of a galaxy preserved in the detailed dynamics of old stellar populations. ER - TY - Journal T1 - Simulations of Galaxy Formation in a Lambda Cold Dark Matter Universe. I. Dynamical and Photometric Properties of a Simulated Disk Galaxy A1 - Abadi, Mario G. A1 - Navarro, Julio F. A1 - Steinmetz, Matthias A1 - Eke, Vincent R. JO - Astrophysical Journal VL - 591 Y1 - 2003/7/1 SP - 499 EP - 514 KW - Cosmology: Theory/ Cosmology: Dark Matter/ Galaxies: Formation/ Galaxies: Structure/ Methods: Numerical UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...591..499A&db_key=AST&high=42a068d47524243 N2 - We present a detailed analysis of the dynamical and photometric properties of a disk galaxy simulated in the Lambda cold dark matter (LambdaCDM) cosmogony. The galaxy is assembled through a number of high-redshift mergers followed by a period of quiescent accretion after z~1 that lead to the formation of two distinct dynamical components: a spheroid of mostly old stars and a rotationally supported disk of younger stars. The surface brightness profile is very well approximated by the superposition of an R^1/4 spheroid and an exponential disk. Each photometric component contributes a similar fraction of the total luminosity of the system, although less than a quarter of the stars form after the last merger episode at z~1. In the optical bands the surface brightness profile is remarkably similar to that of Sab galaxy UGC 615, but the simulated galaxy rotates significantly faster and has a declining rotation curve dominated by the spheroid near the center. The decline in circular velocity is at odds with observation and results from the high concentration of the dark matter and baryonic components, as well as from the relatively high mass-to-light ratio of the stars in the simulation. The simulated galaxy lies ~1 mag off the I-band Tully-Fisher relation of late-type spirals but seems to be in reasonable agreement with Tully-Fisher data on S0 galaxies. In agreement with previous simulation work, the angular momentum of the luminous component is an order of magnitude lower than that of late-type spirals of similar rotation speed. This again reflects the dominance of the slowly rotating, dense spheroidal component, to which most discrepancies with observation may be traced. On its own, the disk component has properties rather similar to those of late-type spirals: its luminosity, its exponential scale length, and its colors are all comparable to those of galaxy disks of similar rotation speed. This suggests that a different form of feedback than adopted here is required to inhibit the efficient collapse and cooling of gas at high redshift that leads to the formation of the spheroid. Reconciling, without fine-tuning, the properties of disk galaxies with the early collapse and high merging rates characteristic of hierarchical scenarios such as LambdaCDM remains a challenging, yet so far elusive, proposition. ER - TY - Journal T1 - Self-similar shocked accretion of collisional gas with radiative cooling A1 - Abadi, Mario G. A1 - Bower, Richard G. A1 - Navarro, Julio F. JO - Monthly Notices of the Royal Astronomical Society VL - 314 Y1 - 2000/6/1 SP - 759 EP - 767 KW - HYDRODYNAMICS/ METHODS: NUMERICAL/ GALAXIES: FORMATION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000MNRAS.314..759A&db_key=AST&high=42a068d47524243 N2 - We describe similarity solutions that characterize the collapse of collisional gas on to scale-free perturbations in an Einstein-de Sitter universe. We consider the effects of radiative cooling and derive self-similar solutions under the assumption that the cooling function is a power law of density and temperature, Lambda(T,rho)~rho^3/2T. We use these results to test the ability of smooth particle hydrodynamics (SPH) techniques to follow the collapse and accretion of shocked, rapidly cooling gas in a cosmological context. Our SPH code reproduces the analytical results very well in cases that include or exclude radiative cooling. No substantial deviations from the predicted central mass accretion rates or from the temperature, density and velocity profiles are observed in well-resolved regions inside the shock radius. This test problem lends support to the reliability of SPH techniques to model the complex process of galaxy formation. ER - TY - Journal T1 - Ram pressure stripping of spiral galaxies in clusters A1 - Abadi, Mario G. A1 - Moore, Ben A1 - Bower, Richard G. JO - Monthly Notices of the Royal Astronomical Society VL - 308 Y1 - 1999/10/1 SP - 947 EP - 954 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.308..947A&db_key=AST&high=42a068d47524243 N2 - We use three-dimensional SPH/N-body simulations to study ram pressure stripping of gas from spiral galaxies orbiting in clusters. We find that the analytic expectation of Gunn & Gott, relating the gravitational restoring force provided by the disc to the ram pressure force, provides a good approximation to the radius at which gas will be stripped from a galaxy. However, at small radii it is also important to consider the potential provided by the bulge component. A spiral galaxy passing through the core of a rich cluster, such as Coma, will have its gaseous disc truncated to ~4kpc, thus losing ~80per cent of its diffuse gas mass. The time-scale for this to occur is a fraction of a crossing time ~10^7yr. Galaxies orbiting within poorer clusters, or inclined to the direction of motion through the intracluster medium, will lose significantly less gas. We conclude that ram pressure alone is insufficient to account for the rapid and widespread truncation of star formation observed in cluster galaxies, or the morphological transformation of Sabs to S0s that is necessary to explain the Butcher-Oemler effect. ER - TY - Journal T1 - Correlation Length of X-Ray-Brightest Abell Clusters A1 - Abadi, Mario G. A1 - Lambas, Diego G. A1 - Muriel, Hernán JO - Astrophysical Journal VL - 507 Y1 - 1998/11/1 SP - 526 EP - 529 KW - GALAXIES: CLUSTERS: GENERAL/ X-RAYS: GALAXIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...507..526A&db_key=AST&high=42a068d47524243 N2 - We compute the cluster autocorrelation function xi_cc(r) of an X-ray flux-limited sample of Abell clusters (XBACs). For the total XBACs sample we find a power-law fit xi_cc = (r/r_0)^gamma with r_0 = 21.1 Mpc h^-1 and gamma = -1.9, consistent with the results of R >= 1 Abell clusters. We also analyze xi_cc(r) for subsamples defined by different X-ray luminosity thresholds where we find a weak tendency of larger values of r_0 with increasing X-ray luminosity, although with a low statistical significance. In the different subsamples analyzed we find 21 Mpc h^-1 < r_0 < 35 Mpc h^-1 and -1.9 < gamma < -1.6. Our analysis suggests that cluster X-ray luminosities may be used for a reliable confrontation of cluster spatial distribution properties in models and observations. ER - TY - Journal T1 - NGC 1566: Spectroscopy of a symmetric system with Seyfert nucleus A1 - Agüero, E. L. A1 - Díaz, R. J. A1 - Bajaja, E. JO - Astronomy and Astrophysics VL - 414 Y1 - 2004/2/1 SP - 453 EP - 461 KW - galaxies: individual: NGC 1566/ galaxies: photometry/ galaxies: nuclei/ galaxies: kinematics and dynamics UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...414..453A&db_key=AST&high=42a068d47503219 N2 - The central region and main body of the very symmetrical galaxy NGC 1566 were observed and studied spectrophotometrically and kinematically. We found that: a) the total masses derived from the Satoh model fitted to the rotation curve, and from the global H I radial velocity profile, are coincident: 2×10¹¹ M_âŠ™, which implies the presence of two galactic subsystems without the need for a massive halo; b) from the rotation curve of the fitted model an outflow motion at the bar tips is confirmed (Delta V~40 km s^-1); c) the observed non-circular motions in some regions with significant blue shifts (Delta V~60 km s^-1) would represent inflows of gas to the nucleus; d) the fitted pattern speed at (23±2) km s^-1 kpc^-1 allows one to explain the radial positions of the inner ring, the star formation ridge of the arms, and the ring at the main disk outer edge, as result of dynamical resonances; e) the nucleus was in a stage of Seyfert 1.8 and in a low level of activity during observations; f) nuclear and inner rings were detected; there is also evidence of a ring at the main disk outer edge; g) some emission regions in the arms have Halpha fluxes higher than in the nucleus; h) the star bursts in the ring at the bar end radius would be younger than in the arms; i) the Halpha emission appears to be correlated with the thermal component of the continuum radiation and with the molecular gas over the whole galaxy. Paper partially supported by a grant from SeCyT, National University of Córdoba, Argentina. ER - TY - Journal T1 - The Merging System AM 2049-691 A1 - Agüero, E. L. A1 - Díaz, R. J. A1 - Paolantonio, S. JO - Publications of the Astronomical Society of the Pacific VL - 113 Y1 - 2001/12/1 SP - 1515 EP - 1521 KW - galaxies: individual (AM 2049-691)/ Galaxies: Nuclei/ Galaxies: Peculiar/ Techniques: Photometric/ Techniques: Spectroscopic UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001PASP..113.1515A&db_key=AST&high=42a068d47503219 N2 - We present photometric and spectroscopic observations of the peculiar object AM 2049-691, whose most remarkable features are (1) two distinct nuclei connected by a bridge and (2) two tails. We studied seven zones and found that they have spectral features typical of H II regions of low excitation, electron temperatures and densities in the range of normal values for such regions, and quite high internal reddening. The derived Halpha+N II equivalent widths suggest enhanced star formation when a comparison is made with isolated galaxies, especially in the northeast nucleus; the equivalent width of the integrated spectrum reflects starburst activity in the whole object, which is compatible with a merger of two disk galaxies. We detected a comparative overabundance of nitrogen relative to oxygen in the southwest nucleus, which has the most evolved population. The bridge between the nuclei was also observed in Halpha emission. B-V colors of the nuclei, after correction for internal absorption, also indicate that they are star-forming regions. The central radial velocity dispersions at the nuclei suggest that the most massive galaxy might be the progenitor of the southwest component. The observed radial velocity distribution shows the presence of two subsystems, each one associated with a different nucleus. ER - TY - Journal T1 - The Peculiar System ESO 244-G012 A1 - Agüero, E. L. A1 - Paolantonio, S. A1 - Günthardt, G. JO - Astronomical Journal VL - 119 Y1 - 2000/1/1 SP - 94 EP - 101 KW - GALAXIES: INDIVIDUAL (ESO 244-G012)/ GALAXIES: NUCLEI/ GALAXIES: PECULIAR/ TECHNIQUES: PHOTOMETRIC/ TECHNIQUES: SPECTROSCOPIC UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....119...94A&db_key=AST&high=42a068d47503219 N2 - We present spectroscopic and photometric observations of the peculiar galaxy ESO 244-G012, the most prominent features of which are two distinct nuclei and a long asymmetric tail visible up to about 40 kpc from the center of the main body. The spectral characteristics of all the observed zones are typical of H II regions of low excitation; their N(N)/N(O) ratios indicate a comparative overabundance of nitrogen with respect to the oxygen. Around the northern nucleus, the internal reddenings, the excitations, the equivalent widths, and the derived abundances are systematically different from those of the southern one, suggesting they have had different evolutions. The equivalent width of the Halpha+[N II] lines of the northern nucleus indicates it is a starburst; that of the southern one is compatible with a Sb galaxy. The Halpha+[N II] equivalent width of the integrated spectrum is comparable with those observed in mergers of two disk galaxies. The starburst nature of the northern nucleus, observed in the optical range, is in agreement with the properties of ESO 244-G012 detected in the far IR and with the CO and radio observations. In this object, one of the nuclei dominates the IR emission, and the enhancement of the star formation activity is observed in only one of them. The integrated total color B-V corresponds to an Sa-Sab galaxy. The integrated colors B-V,V-R,R-I, and B-I do not show big radial variations reflecting a rather uniform population, on average, which would be between G8 and K0 types. Indicative B-V colors of the nuclei, corrected for internal absorption, give very different results, and that of the northern nucleus suggests it is an active star-forming region as found from the spectroscopic data. The velocity distribution of ESO 244-G012 has two branches, being similar to that of other system which also has two nuclei. The derived data would indicate that ESO 244-G012 is a merger system; the two distinct visible nuclei suggest that the components are still interacting. ER - TY - Journal T1 - The System ESO 296-IG11 A1 - Agüero, E. L. A1 - Paolantonio, S. A1 - Günthardt, G. JO - Astronomical Journal VL - 117 Y1 - 1999/3/1 SP - 1151 EP - 1157 KW - GALAXIES: INDIVIDUAL: ALPHANUMERIC: ESO 296-IG11/ GALAXIES: PECULIAR/ ISM: H II REGIONS/ TECHNIQUES: PHOTOMETRIC/ TECHNIQUES: SPECTROSCOPIC UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....117.1151A&db_key=AST&high=42a068d47503219 N2 - We present photometric and spectroscopic observations of the system ESO 296-IG11, which is composed of two galaxies, as well as observations of a small galaxy 1.3' distant. Colors through the entire system show little variation and reflect the presence of about the same young stellar composition. The quite blue colors of the observed regions in both galaxies of the system indicate star formation activity, and the distribution of the regions through the bodies of the galaxies suggests that a quite generalized starburst has taken place. The spectra of these regions are characteristic of H II regions of comparatively high excitation; their oxygen and nitrogen abundances are low, and their N(N)/N(O) ratios are comparable to those of the Magellanic Clouds and late spiral galaxies. The low abundances of the regions would be consistent with the ages derived for the bursts of star formation in their interiors. The high equivalent widths of the Halpha+[N II] emission lines of the integrated spectra of both galaxies indicate enhanced star formation rates compared with isolated galaxies and are compatible with those observed in mergers of two disk galaxies. The velocities indicate that the two galaxies are a physical pair and that they are linked with the small nearby galaxy. The derived information suggests that ESO 296-IG11 is composed of two advanced late-type galaxies with similar general properties, which, together with the small nearby galaxy, constitute a triple system. ER - TY - Journal T1 - The Peculiar Galaxy NGC 1487 A1 - Aguero, E. L. A1 - Paolantonio, S. JO - Astronomical Journal VL - 114 Y1 - 1997/7/1 SP - 102 KW - GALAXIES: INDIVIDUAL: NGC 1487/ GALAXIES: PECULIAR UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997AJ....114..102A&db_key=AST&high=42a068d47503219 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..102A&db_key=AST ER - TY - Journal T1 - Spectra of Four IRAS-Selected AGN Candidates A1 - Aguero, E. L. A1 - Paolantonio, S. A1 - Suarez, F. JO - Publications of the Astronomical Society of the Pacific VL - 108 Y1 - 1996/12/1 SP - 1117 EP - 1119 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996PASP..108.1117A&db_key=AST&high=42a068d47503219 N2 - Observations of four southern warm IRAS objects are presented. From their optical spectral characteristics they are classified according to their principal excitation mechanisms: one as a Seyfert 2 type, two others as H II region-like galaxies (one of them is a starburst galaxy); the proposed optical identification for the remaining IRAS object is a star of early K type. Their heliocentric radial velocities are given. Additional observations of other eight IRAS galaxies are also reported, basically confirming previous results with slight variations in redshifts and classifications. (SECTION: Quasars and Active Galactic Nuclei) ER - TY - Journal T1 - Spectral Emission of a Sample of IRAS Galaxies. II A1 - Aguero, E. L. A1 - Suarez, F. A1 - Paolantonio, S. JO - Publications of the Astronomical Society of the Pacific VL - 107 Y1 - 1995/10/1 SP - 959 KW - GALAXIES: ACTIVE/ SEYFERT UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995PASP..107..959A&db_key=AST&high=42a068d47503219 N2 - Observations of seven objects selected from the de Grijp et al. Catalog of AGN candidates (1987) and two from the list of Maia et al. (1987) are reported. From their optical spectral characteristics they are classified according to their degree of nuclear activity: two of them as Seyfert 2 types, two others as Seyfert 1.9 types, one as a Liner, adn three as H II region-like galaxies; the reamining one turns out to be a star. Far infrared properties are also used to analyze these objects. Very good correlations between the far IR luminosity and H-alpha and [O III] lambda-5007 luminosities are found for the Seyfert galaxies. The far infrared luminosity of these seems to depend on both, the amount of the dust present and strongly on the number of ionizing photons. (SECTION: Galaxies) ER - TY - Journal T1 - Dating star clusters in the Small Magellanic Cloud by means of integrated spectra A1 - Ahumada, A. V. A1 - Clariá, J. J. A1 - Bica, E. A1 - Dutra, C. M. JO - Astronomy and Astrophysics VL - 393 Y1 - 2002/10/1 SP - 855 EP - 866 KW - methods: observational/ techniques: spectroscopic/ galaxies: Small Magellanic Cloud/ star clusters UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...393..855A&db_key=AST&high=42a068d47504352 N2 - In this study flux-calibrated integrated spectra in the range (3600-6800) Å are presented for 16 concentrated star clusters in the Small Magellanic Cloud (SMC), approximately half of which constitute unstudied objects. We have estimated ages and foreground interstellar reddening values from the comparison of the line strengths and continuum distribution of the cluster spectra with those of template cluster spectra with known parameters. Most of the sample clusters are young blue clusters (6-50 Myr), while L 28, NGC 643 and L 114 are found to be intermediate-age clusters (1-6 Gyr). One well known SMC cluster (NGC 416) was observed for comparison purposes. The sample includes clusters in the surroundings and main body of the SMC, and the derived foreground reddening values are in the range 0.00 <= E(B-V) <= 0.15. The present data also make up a cluster spectral library at SMC metallicity. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina. ER - TY - Journal T1 - Reddening and age for 13 southern Galactic open clusters determined from integrated spectra A1 - Ahumada, A. V. A1 - Clariá, J. J. A1 - Bica, E. A1 - Dutra, C. M. A1 - Torres, M. C. JO - Astronomy and Astrophysics VL - 377 Y1 - 2001/10/1 SP - 845 EP - 853 KW - METHODS: OBSERVATIONAL/ TECHNIQUES: SPECTROSCOPIC/ OPEN CLUSTERS AND ASSOCIATIONS: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...377..845A&db_key=AST&high=42a068d47504352 N2 - In this study we present flux-calibrated integrated spectra in the range 3800-6800 Å for 13 concentrated open clusters with Galactic longitudes between 219^deg and 316^deg, nine of which have not been previously studied. Using the equivalent widths of the Balmer lines and comparing the cluster spectra with template spectra of Magellanic Clouds and Galactic star clusters with known parameters, we derive both foreground interstellar reddening values and age. For nine clusters these two parameters have been determined for the first time, while for the rest of the sample the results show good agreement with previous studies. The present analysis indicates four very young (Hogg 11, NGC 5606, vdB-RN 80 and Pismis 17), seven moderately young (ESO 429-SC13, Hogg 3, Hogg 12, Haffner 7, BH 87, NGC 2368 and Bochum 12) and two intermediate-age (Berkeley 75 and NGC 2635) open clusters. The derived foreground interstellar reddening values are in the range 0.00 <= E(B-V) <= 0.38. The age and reddening distributions of the present sample of relatively faint open clusters match those of open clusters with known parameters in a 90^deg sector centered at l = 270^deg. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina. ER - TY - Journal T1 - Integrated spectral properties of 7 galactic open clusters A1 - Ahumada, A. V. A1 - Clariá, J. J. A1 - Bica, E. A1 - Piatti, A. E. JO - Astronomy and Astrophysics Supplement Series VL - 141 Y1 - 2000/1/1 SP - 79 EP - 88 KW - TECHNIQUES: SPECTROSCOPIC/ OPEN CLUSTERS: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26AS..141...79A&db_key=AST&high=42a068d47504352 N2 - This paper presents flux-calibrated integrated spectra in the range 3600-9000 Ä for 7 concentrated, relatively populous Galactic open clusters. We perform simultaneous estimates of age and foreground interstellar reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of template cluster spectra with known parameters. For five clusters these two parameters have been determined for the first time (Ruprecht 144, BH 132, Pismis 21, Lyng\aa 11 and BH 217), while the results here derived for the remaining two clusters (Hogg 15 and Melotte 105) show very good agreement with previous studies based mainly on colour-magnitude diagrams. We also provide metallicity estimates for six clusters from the equivalent widths of CaII triplet and TiO features. The present cluster sample improves the age resolution around solar metal content in the cluster spectral library for population synthesis. We compare the properties of the present sample with those of clusters in similar directions. Hogg 15 and Pismis 21 are among the most reddened clusters in sectors centered at l = 270^o and l = 0^o, respectively. Besides, the present results would favour an important dissolution rate of star clusters in these zones. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina. ER - TY - Journal T1 - CCD Photometry of the Open Clusters NGC 2658, NGC 2849, and NGC 3247 A1 - Ahumada, J. A. JO - Revista Mexicana de Astronomia y Astrofisica VL - 39 Y1 - 2003/4/1 SP - 41 EP - 53 KW - Open clusters and associations: general/ Open clusters and associations: individual (NGC 2658/ NGC 2849/ NGC 3247) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003RMxAA..39...41A&db_key=AST&high=42a068d47511340 N2 - We present CCD photometry of the galactic open clusters NGC 2658, NGC 2849, and NGC 3247. By means of the comparison between the observed cluster sequences and the Padova theoretical isochrones, we derive the following parameters: for NGC 2658, E(B-V) =0.35^+0.05_-0.10 , log(age) = 8.50^+0.25_-0.05, and (m - M)₀ = 13.32^+0.36_-0.52; for NGC 2849, the reddening is in the range 0.46 to 0.57 with an uncertainty of +/-0.12 mag, (m - M)₀ = 14.02^+0.38_-0.40, and log(age) = 8.8^+0.1_-0.05; finally, for NGC 3247 we obtain E(B-V)=0.39±0.07 , log(age) = 7.60^+0.4_-0.3, and (m - M)₀ = 11.89^+0.51_-0.45. In this study the isochrones have been renormalized to the solar values (B-V)_âŠ™ =0.65 and M[V] = 4.84; the values ( {V-R)_âŠ™ =0.37 and (V-I)_âŠ™ =0.70 are proposed as zero points in order to renormalize those colors as well. ER - TY - Journal T1 - Catalogue of blue stragglers in open clusters. A1 - Ahumada, J. A1 - Lapasset, E. JO - Astronomy and Astrophysics Supplement Series VL - 109 Y1 - 1995/2/1 SP - 375 EP - 382 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26AS..109..375A&db_key=AST&high=42a068d47511340 N2 - An extensive survey of blue straggler candidates in galactic open clusters of both hemispheres is presented. The blue stragglers were selected considering their positions in the cluster colour-magnitude diagrams.They were categorized according to the accuracy of the photometric measurements and membership probabilities. An amount of 959 blue straggler candidates in 390 open clusters of all ages were identified and classified. A set of basic data is given for every cluster and blue straggler. The information is arranged in the form of a catalogue. Blue stragglers are found in clusters of all ages. The percentage of clusters with blue stragglers generally grows with age and richness of the clusters. The mean ratio of the number of blue stragglers to the number of cluster main sequence stars is approximately constant up to a cluster age of about 10^8.6^ yr and rises for older clusters. In general, the blue stragglers show a remarkable degree of central concentration. ER - TY - Journal T1 - Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry A1 - Alonso, M. V. A1 - Bernardi, M. A1 - da Costa, L. N. A1 - Wegner, G. A1 - Willmer, C. N. A. A1 - Pellegrini, P. S. A1 - Maia, M. A. G. JO - Astronomical Journal VL - 125 Y1 - 2003/5/1 SP - 2307 EP - 2324 KW - Cosmology: Observations/ Galaxies: Clusters: General/ Galaxies: Photometry/ Cosmology: Large-Scale Structure of Universe UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....125.2307A&db_key=AST&high=42a068d47513446 N2 - We present R-band CCD photometry for 1332 early-type galaxies, observed as part of the ENEAR survey of peculiar motions using early-type galaxies in the nearby universe. Circular apertures are used to trace the surface brightness profiles, which are then fitted by a two-component bulge-disk model. From the fits, we obtain the structural parameters required to estimate galaxy distances using the D_n-sigma and fundamental plane relations. We find that about 12% of the galaxies are well represented by a pure r^1/4 law, while 87% are best fitted by a two-component model. There are 356 repeated observations of 257 galaxies obtained during different runs that are used to derive statistical corrections and bring the data to a common system. We also use these repeated observations to estimate our internal errors. The accuracy of our measurements are tested by the comparison of 354 galaxies in common with other authors. Typical errors in our measurements are 0.011 dex for logD_n, 0.064 dex for logr_e, 0.086 mag arcsec^-2 for e>, and 0.09 for m_{R_C}, comparable to those estimated by other authors. The photometric data reported here represent one of the largest high-quality and uniform all-sky samples currently available for early-type galaxies in the nearby universe, especially suitable for peculiar motion studies. Based on observations at Cerro Tololo Inter-American Observatory (CTIO), National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation (NSF); European Southern Observatory (ESO); Fred Lawrence Whipple Observatory (FLWO); and the MDM Observatory on Kitt Peak. ER - TY - Journal T1 - The double-layered chemical structure in DB white dwarfs A1 - Althaus, L. G. A1 - Córsico, A. H. JO - Astronomy and Astrophysics VL - 417 Y1 - 2004/4/1 SP - 1115 EP - 1123 KW - stars: evolution/ stars: interiors/ stars: white dwarfs/ stars: oscillations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...417.1115A&db_key=AST&high=42a068d47522694 N2 - The purpose of this work is to study the structure and evolution of white dwarf stars with helium-rich atmospheres (DB) in a self-consistent way with the predictions of time-dependent element diffusion. Specifically, we have considered white dwarf models with stellar masses in the range 0.60-0.85 M_âŠ™ and helium envelopes with masses from 10^-2 to 10^-4 M_*. Our treatment of diffusion, appropriate for multicomponent gases, includes gravitational settling and chemical and thermal diffusion. OPAL radiative opacities for arbitrary metallicity and carbon-and oxygen-rich compositions are employed. Emphasis is placed on the evolution of the diffusion-modeled double-layered chemical structure. This structure, which is characterized by a pure helium envelope atop an intermediate remnant shell rich in helium, carbon and oxygen, is expected for pulsating DB white dwarfs, assuming that they are descendants of hydrogen-deficient PG 1159 post-AGB stars. We find that, depending on the stellar mass, if DB white dwarf progenitors are formed with a helium content smaller than â‰ˆ10^-3 M_*, a single-layered configuration is expected to emerge during the DB pulsation instability strip. We also explore the consequences of diffusively evolving chemical stratifications on the adiabatic pulsational properties of our DB white dwarf models. In this context, we find that the evolving shape of the chemical profile translates into a distinct behaviour of the theoretical period distribution as compared with the case in which the shape of the profile is assumed to be fixed during the evolution across the instability strip. In particular, we find that the presence of a double-layered structure causes the period spacing diagrams to exhibit mode-trapping substructures. Finally, we extend the scope of the calculations to the domain of the helium-rich carbon-contaminated DQ white dwarfs. In particular, we speculate that DQ white dwarfs with low detected carbon abundances would not be descendants of the PG 1159 stars. ER - TY - Journal T1 - Evolutionary and pulsational properties of low-mass white dwarf stars with oxygen cores resulting from close binary evolution A1 - Althaus, L. G. A1 - Córsico, A. H. A1 - Gautschy, A. A1 - Han, Z. A1 - Serenelli, A. M. A1 - Panei, J. A. JO - Monthly Notices of the Royal Astronomical Society VL - 347 Y1 - 2004/1/1 SP - 125 EP - 136 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.347..125A&db_key=AST&high=42a068d47522694 N2 - The present work is designed to explore the evolutionary and pulsational properties of low-mass white dwarfs with carbon/oxygen cores. In particular, we follow the evolution of a 0.33-M_solar white dwarf remnant in a self-consistent way with the predictions of nuclear burning, element diffusion and the history of the white dwarf progenitor. Attention is focused on the occurrence of hydrogen shell flashes induced by diffusion processes during cooling phases. The evolutionary stages prior to the white dwarf formation are also fully accounted for by computing the conservative binary evolution of an initially 2.5-M_solar Population I star with a 1.25-M_solar companion, and with period P_i= 3 d. Evolution is followed down to the domain of the ZZ Ceti stars on the white dwarf cooling branch. We find that chemical diffusion induces the occurrence of an additional hydrogen thermonuclear flash, which leads to stellar models with thin hydrogen envelopes. As a result, a fast cooling is encountered at advanced stages of evolution. In addition, we explore the adiabatic pulsational properties of the resulting white dwarf models. As compared with their helium-core counterparts, low-mass oxygen-core white dwarfs are characterized by a pulsational spectrum much more featured, an aspect which could eventually be used for distinguishing both types of stars, if low-mass white dwarfs were in fact found to pulsate as ZZ Ceti-type variables. Finally, we perform a non-adiabatic pulsational analysis on the resulting carbon/oxygen low-mass white dwarf models. ER - TY - Journal T1 - New evolutionary models for massive ZZ Ceti stars. I. First results for their pulsational properties A1 - Althaus, L. G. A1 - Serenelli, A. M. A1 - Córsico, A. H. A1 - Montgomery, M. H. JO - Astronomy and Astrophysics VL - 404 Y1 - 2003/6/1 SP - 593 EP - 609 KW - stars: evolution/ stars: abundances/ stars: AGB stars: interiors/ stars: white dwarfs/ stars: oscillations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...404..593A&db_key=AST&high=42a068d47522694 N2 - We present new and improved evolutionary calculations for carbon-oxygen white dwarf (WD) stars appropriate for the study of massive ZZ Ceti stars. To this end, we follow the complete evolution of massive WD progenitors from the zero-age main sequence through the thermally pulsing and mass loss phases to the WD regime. Abundance changes are accounted for by means of a full coupling between nuclear evolution and time-dependent mixing due to diffusive overshoot, semiconvection and salt fingers. In addition, time-dependent element diffusion for multicomponent gases has been considered during the WD stage. Emphasis is placed on the chemistry variations along the whole evolution. In particular, we find that before the ZZ Ceti stage is reached, element diffusion has strongly smoothed out the chemical profile to such a degree that the resulting internal abundance distribution does not depend on the occurrence of overshoot episodes during the thermally pulsing phase. The mass of the hydrogen envelope left at the ZZ Ceti domain amounts to M_H ~ 2.3 x 10^-6 M_sun. This is about half as large as for the case when element diffusion is neglected. The implications of our new models for the pulsational properties of massive ZZ Ceti stars are discussed. In this regard, we find that the occurrence of core overshooting during central helium burning leaves strong imprints on the theoretical period spectrum of massive ZZ Ceti stars. Finally, we present a simple new prescription for calculating the He/H profile which goes beyond the trace element approximation. ER - TY - Journal T1 - Evolution of a 3-M_solar star from the main sequence to the ZZ Ceti stage: the role played by element diffusion A1 - Althaus, L. G. A1 - Serenelli, A. M. A1 - Córsico, A. H. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 330 Y1 - 2002/3/1 SP - 685 EP - 698 KW - STARS: EVOLUTION/ STARS: INTERIORS/ STARS: OSCILLATIONS/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.330..685A&db_key=AST&high=42a068d47522694 N2 - The purpose of this paper is to present new full evolutionary calculations for DA white dwarf stars with the major aim of providing a physically sound reference frame for exploring the pulsation properties of the resulting models in future communications. Here, white dwarf evolution is followed in a self-consistent way with the predictions of time-dependent element diffusion and nuclear burning. In addition, full account is taken of the evolutionary stages prior to white dwarf formation. In particular, we follow the evolution of a 3-M_solar model from the zero-age main sequence (the adopted metallicity is , all the way from the stages of hydrogen and helium burning in the core up to the thermally pulsing phase. After experiencing 11 thermal pulses, the model is forced to evolve towards its white dwarf configuration by invoking strong mass loss episodes. Further evolution is followed down to the domain of the ZZ Ceti stars on the white dwarf cooling branch. Emphasis is placed on the evolution of the chemical abundance distribution caused by diffusion processes and the role played by hydrogen burning during the white dwarf evolution. We find that discontinuities in the abundance distribution at the start of the cooling branch are considerably smoothed out by diffusion processes by the time the ZZ Ceti domain is reached. Nuclear burning during the white dwarf stage does not represent a major source of energy, as expected for a progenitor star of initially high metallicity. We also find that thermal diffusion lessens even further the importance of nuclear burning. Furthermore, the implications of our evolutionary models for the main quantities relevant for adiabatic pulsation analysis are discussed. Interestingly, the shape of the Ledoux term is markedly smoother compared with previous detailed studies of white dwarfs. This is translated into a different behaviour of the Brunt-Väisälä frequency. ER - TY - Journal T1 - The impact of element diffusion on the formation and evolution of helium white dwarf stars A1 - Althaus, L. G. A1 - Serenelli, A. M. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 324 Y1 - 2001/6/1 SP - 617 EP - 622 KW - DIFFUSION/ STARS: EVOLUTION/ STARS: INTERIORS/ PULSARS: GENERAL/ PULSARS: INDIVIDUAL: PSR B1855+09/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.324..617A&db_key=AST&high=42a068d47522694 N2 - The aim of this work is to investigate the effect of element diffusion on the evolution of helium white dwarfs. To this end, we couple the multicomponent flow equations that describe gravitational settling, chemical and thermal diffusion to an evolutionary code. We compute the evolution of a set of helium white dwarf models with masses ranging from 0.169 to 0.406M_solar. In particular, several low-mass white dwarfs have been found in binary systems as companion to millisecond pulsars. In these systems, pulsar emission is activated by mass transfer episodes so that, if we place the zero-age point at the end of such mass transfer, then the pulsar and the white dwarf ages should be equal. Interestingly enough, available models of helium white dwarfs neglect element diffusion. Using such models, good agreement has been found between the ages of the components of the PSR J1012+5307 system. However, recent observations of the PSR B1855+09 system cast doubts on the correctness of such models, which predict a white dwarf age twice as long as the spin-down age of the pulsar. In this work, we find that element diffusion induces thermonuclear hydrogen shell flashes for models in the mass interval 0.18<~M/M_solar<~0.41. We show, in particular, that the occurrence of these diffusion-induced flashes eventually leads to white dwarf models with hydrogen envelope masses too small to support any further nuclear burning, thus implying much shorter cooling ages than in the case when diffusion is neglected. In particular, excellent agreement is found between the ages of PSR B1855+09 system components, solving the age discrepancy from first principles. ER - TY - Journal T1 - Formation and Evolution of a 0.242 M_solar Helium White Dwarf in the Presence of Element Diffusion A1 - Althaus, L. G. A1 - Serenelli, A. M. A1 - Benvenuto, O. G. JO - Astrophysical Journal VL - 554 Y1 - 2001/6/1 SP - 1110 EP - 1117 KW - Stars: Pulsars: General/ Stars: Evolution/ Stars: Interiors/ Stars: White Dwarfs UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...554.1110A&db_key=AST&high=42a068d47522694 N2 - The evolution of a 0.242 M_solar object that finally becomes a helium white dwarf is modeled from Roche lobe detachment down to very low luminosities (log L/L_solar=-5). In doing so, we employ our stellar code, to which we have added a set of routines that compute the effects due to gravitational settling and chemical and thermal diffusion. Initial models are constructed by abstracting mass from a 1 M_solar red giant branch model up to the moment at which the model begins to evolve blueward. From then on, two detailed sequences have been computed: one sequence with element diffusion and the other without that phenomenon. Results without diffusion are very similar to those of Driebe and collaborators. We find that element diffusion introduces important changes in the internal structure of the star. In particular, models with diffusion undergo three thermonuclear flashes, whereas models without diffusion experience only one. This fact has a large effect on the fraction of total hydrogen mass left in the star (about 3 times less hydrogen compared to models without diffusion) at the start of the final cooling track. As a result, at late stages of evolution models with diffusion are characterized by a much smaller nuclear energy release. Consequently, the star has to take energy from its relic thermal content, causing its further evolution to be significantly faster compared with the standard treatment. Notably, these new, more detailed structures strongly resemble those we have assumed in previous work on helium white dwarfs with hydrogen envelopes. Conventional wisdom indicates that a millisecond pulsar is recycled during the mass transfer stage in a binary system. Usually, the companion to the pulsar is a low-mass white dwarf. If zero ages are set at the end of mass transfer, the ages of both objects should be the same. Available models characterized by dominant hydrogen burning lead to a strong discrepancy between the ages of PSR B1855+09 and its white dwarf companion. We interpret such a discrepancy as a direct consequence of ignoring element diffusion in the stellar models. We show that in the frame of models in which diffusion is properly accounted for, ages naturally come into a nice agreement. Consequently, we do not have to invoke any ad hoc mass loss or exotic mechanisms to account for the ages of the stars that belong to the binary system PSR B1855+09. ER - TY - Journal T1 - Diffusion and the occurrence of hydrogen-shell flashes in helium white dwarf stars A1 - Althaus, L. G. A1 - Serenelli, A. M. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 323 Y1 - 2001/5/1 SP - 471 EP - 483 KW - DIFFUSION/ STARS: EVOLUTION/ STARS: INTERIORS/ PULSARS: GENERAL/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.323..471A&db_key=AST&high=42a068d47522694 N2 - In this paper we investigate the effects of element diffusion on the structure and evolution of low-mass helium white dwarfs. Attention is focused mainly on the occurrence of hydrogen-shell flashes induced by diffusion processes during cooling phases. Physically sound initial models with stellar masses of 0.406, 0.360, 0.327, 0.292, 0.242, 0.196, 0.169 and 0.161M_solar are constructed by applying mass-loss rates at different stages of the red giant branch evolution of a solar model up to the moment the model begins to evolve to the blue part of the HR diagram. The multicomponent flow equations describing gravitational settling, and chemical and thermal diffusion are solved and the diffusion calculations are coupled to an evolutionary code. In addition, the same sequences are computed but neglecting diffusion. Results without diffusion are similar to recent results of Driebe, Schönberner, Blöcker and Herwig. We find that element diffusion strongly affects the structure and cooling history of helium white dwarfs. In particular, diffusion induces the occurrence of hydrogen-shell flashes in models with masses ranging from 0.18 to 0.41M_solar, which is in sharp contrast with the situation when diffusion is neglected. In connection with further evolution, these diffusion-induced flashes lead to much thinner hydrogen envelopes, preventing stable nuclear burning from being a sizeable energy source at advanced stages of evolution. This implies much shorter cooling ages than in the case when diffusion is neglected. These new evolutionary models are discussed in light of recent observational data on some millisecond pulsar systems with white dwarf companions. In this context, we find that discrepancies between spin-down ages and the predictions of standard evolutionary models appear to be the result of ignoring element diffusion in such evolutionary models. Indeed, such discrepancies vanish when account is taken of diffusion. ER - TY - Journal T1 - Diffusion in helium white dwarf stars A1 - Althaus, L. G. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 317 Y1 - 2000/10/1 SP - 952 EP - 964 KW - STARS: EVOLUTION/ STARS: INTERIORS/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000MNRAS.317..952A&db_key=AST&high=42a068d47522694 N2 - This paper is aimed at exploring the effects of diffusion on the structure and evolution of low-mass helium white dwarfs. To this end, we solve the multicomponent flow equations describing gravitational settling and chemical and thermal diffusion. The diffusion calculations are coupled to an evolutionary code in order to follow the cooling of low-mass, helium core white dwarf models having envelopes made up of a mixture of hydrogen and helium, as recently suggested by detailed evolutionary calculations for white dwarf progenitors in binary systems. We find that diffusion causes hydrogen to float and the other elements to sink over time-scales shorter than evolutionary time-scales. This produces a noticeable change in the structure of the outer layers, making the star inflate. Thus, in order to compute accurately the mass-radius relation for low-mass helium white dwarfs we need to account for the diffusion processes during (at least) the white dwarf stages of the evolution of these objects. This should be particularly important when studying the general characteristics of binary systems containing a helium white dwarf and a pulsar. In addition, we present an analytic, approximate model for the outer layers of the white dwarf aimed at interpreting the physical reasons for the change in the surface gravity for low-mass white dwarfs induced by diffusion. ER - TY - Journal T1 - Evolution of DA white dwarfs in the context of a new theory of convection A1 - Althaus, L. G. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 296 Y1 - 1998/5/1 SP - 206 EP - 216 KW - CONVECTION/ STARS: EVOLUTION/ STARS: VARIABLES: OTHER/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998MNRAS.296..206A&db_key=AST&high=42a068d47522694 N2 - In this study we compute the structure and evolution of carbon-oxygen DA (hydrogen-rich envelope) white dwarf models by means of a detailed and updated evolutionary code. We consider models with masses from 0.5 to 1.0Msolar and we vary the hydrogen layer mass in the interval 10^-13<=M_H/Mâ‰®10^-4. In particular, we treat the energy transport by convection within the formalism of the full-spectrum turbulence theory, as given by the Canuto, Goldman & Mazzitelli (CGM) model. We explore the effect of various hydrogen layer masses on both the surface gravity and the hydrogen burning. Convective mixing at low luminosities is also considered. One of our main interests in this work has been to study the evolution of ZZ Ceti models, with the aim of comparing the CGM and mixing-length theory (MLT) predictions. In this connection, we find that the temperature profile given by the CGM model is markedly different from that of the ML1 and ML2 versions of the MLT. In addition, the evolving outer convection zone behaves differently in both theories. We have also computed approximate effective temperatures for the theoretical blue edge of the DA instability strip by using thermal time-scale arguments for our evolving DA models. In this context, we found that the CGM theory leads to blue edges that are cooler than the observed ones. However, because the determination of atmospheric parameters of ZZ Ceti stars is dependent on the assumed convection description in model atmosphere calculations, observed blue edges based on model atmospheres computed considering the CGM theory are required in order to perform a self-consistent comparison of our results with observations. Finally, detailed non-adiabatic pulsational computations of ZZ Ceti models considering the CGM convection would be necessary to place the results found in this paper on a firmer basis. ER - TY - Journal T1 - New theories of convection in the context of a recent analysis of the DBV white dwarf GD 358 A1 - Althaus, L. G. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 288 Y1 - 1997/6/1 SP - L35 EP - L38 KW - CONVECTION/ STARS: INDIVIDUAL: GD 358/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997MNRAS.288L..35A&db_key=AST&high=42a068d47522694 N2 - We present updated evolutionary calculations for carbon-oxygen DB white dwarfs using the self-consistent model for turbulent convection recently developed by Canuto, Goldman & Mazzitelli (CGM). To this end, we employ a detailed stellar evolutionary code in which we include a new equation of state for helium plasmas computed by Saumon, Chabrier & Van Horn as well as new OPAL radiative opacities. The present study is aimed at assessing the compatibility of the CGM model with the recent effective temperature redetermination of the pulsating DB white dwarf star GD 358. This star defines the blue edge of the DB white dwarf instability strip. Using thermal time-scale arguments, we find that the DB blue edges given by the CGM fit to the effective temperature of GD 358 are much better than those given by the previous Canuto & Mazzitelli model. ER - TY - Journal T1 - Evolution of Helium White Dwarfs of Low and Intermediate Masses A1 - Althaus, L. G. A1 - Benvenuto, O. G. JO - Astrophysical Journal VL - 477 Y1 - 1997/3/1 SP - 313 KW - STARS: PULSARS: GENERAL/ STARS: EVOLUTION/ STARS: INTERIORS/ STARS: WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...477..313A&db_key=AST&high=42a068d47522694 N2 - We present detailed calculations of the evolution of low-mass, helium white dwarf models with masses from M = 0.1 to M = 0.5 MâŠ™ at intervals of 0.05 MâŠ™ and with a metallicity of Z = 10-3. For this purpose, we have taken fully into account finite-temperature effects by means of a detailed and updated stellar evolutionary code, in which the convective energy transport is described according to the new model for turbulent convection developed by Canuto & Mazzitelli. Furthermore, our code considers the most recent opacity data computed by the Livermore Group (OPAL data), and also the new equation of state for helium plasmas developed by Saumon, Chabrier, & Van Horn. Neutrino emission is fully taken into account as well. For models with M <= 0.3 MâŠ™ we started our calculations from fully convective models located at the helium-Hayashi line for each configuration, far away from the white dwarf regime. By contrast, the evolutionary sequences corresponding to 0.35, 0.4, 0.45, and 0.5 MâŠ™ were started from initial models resembling white dwarf structures. This was necessary in order to avoid the onset of helium burning. A consequence of this constraint is the existence of a "forbidden region" in the HR diagram above log (L/LâŠ™) = -0.25 and hotter than log Teff = 4.45, where helium white dwarfs can exist only for brief intervals. All the models were evolved to log (L/LâŠ™) = -5. The evolutionary tracks in the HR diagram have been carefully analyzed, and we found that the convective efficiency affects the tracks noticeably only in the high-luminosity (pre--white dwarf) regime. We also examined the evolution of central conditions, neutrino luminosity, radii, surface gravity, and ages. Central densities, radii, and surface gravities asymptotically approach the zero temperature Hamada-Salpeter results, as expected. Neutrino losses are important for the more massive helium white dwarf configurations and should be taken into account in detailed evolutionary studies of these objects. Finally, the structure of the outer convective zone was analyzed in both the framework of the mixing length theory (for different convective efficiencies) and the Canuto & Mazzitelli theory. We found that the profile of the outer convective zone given by the Canuto & Mazzitelli model is very different from that given by any version of the mixing length theory. This behavior is critical for pulsational instability; however, stellar parameters such as radius and surface gravity are not significantly affected in the white dwarf domain. These models should be especially suitable for the interpretation of the data about the recently discovered low-mass white dwarfs in systems containing another white dwarf or a millisecond pulsar. ER - TY - Journal T1 - Evolution of DB white dwarfs in the Canuto and Mazzitelli theory of convection A1 - Althaus, L. G. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 278 Y1 - 1996/2/1 SP - 981 EP - 984 KW - CONVECTION/ STARS: EVOLUTION/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996MNRAS.278..981A&db_key=AST&high=42a068d47522694 N2 - We compute the evolution of DB (helium-rich envelope) white dwarf models with masses between 0.4 and 1M_solar and metallicities of Z=0.001 and 0.004, taking into account Canuto & Mazzitelli's new theory of convection. This theory, which has no free parameters and includes the full spectrum of turbulent eddies, has been successfully tested in different stellar objects and represents a substantial improvement compared with the classical mixing length theory used in most white dwarf studies. Using thermal time-scales we find that, for the range of masses and metallicities assumed in this study, the Canuto & Mazzitelli theory yields theoretical blue edges between 24200 and 25600K, which is in good aggreement with observations of pulsating DB white dwarfs. Calculations are performed considering the mixing length theory as well. In this context, our results are consistent with previous computations. ER - TY - Journal T1 - Microvariability in the optical polarization of 3C 279 A1 - Andruchow, I. A1 - Cellone, S. A. A1 - Romero, G. E. A1 - Dominici, T. P. A1 - Abraham, Z. JO - Astronomy and Astrophysics VL - 409 Y1 - 2003/10/1 SP - 857 EP - 865 KW - galaxies: active/ galaxies: individual: 3C 279/ polarization/ galaxies: photometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...409..857A&db_key=AST&high=42a068d47527546 N2 - We present results of a microvariability polarization study in the violently variable quasar 3C279. We have resolved the polarization curves in the V band for this object down to timescales of minutes. We found two main components in the evolution of the degree of linear polarization, one consisting of a flicker with timescales of several tens of minutes and other component with far more significant variations on timescales of a few days. The linear polarization descended from ~ 17% down to ~ 8% in three nights. The polarization angle underwent a sudden change of more that 10 degrees in a few hours, perhaps indicating the injection of a new shock in the jet. The amplitude of the intranight flickering in the degree of polarization is at the level of ~ 1%. These are probably the best sampled polarization data ever obtained for this object. We also performed IR observations and we provide a follow-up of the evolution of this source at such energies after the main polarization outburst. Based on observations made at the Complejo Astronómico El Leoncito, which is operated under agreement between CONICET and the National Universities of La Plata, Córdoba, and San Juan, as well as at the Laboratório Nacional de Astrofísica, LNA-CNPq, Brazil.}\fnmsep\thanks{Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via \ http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/409/857 ER - TY - Journal T1 - Letter: On a Semi-Numeric Method to Study the Evolution of a General-Relativistic Radiating Shell and X-Ray Bursters A1 - Aquilano, Roberto JO - General Relativity and Gravitation VL - 35 Y1 - 2003/9/1 SP - 1715 EP - 1719 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GReGr..35.1715A&db_key=AST&high=42a068d47530158 N2 - A semi-numeric method was used to study the evolution of a radiating shell in its Post-Newtonian and Newtonian approximations. The solutions, show that a relativistic effect can be found in collapsed stars (X and gamma ray bursters). ER - TY - Journal T1 - Addendum to ``Mathematical structure of quantum superspace as a consequence of time asymmetry'' A1 - Aquilano, Roberto A1 - Castagnino, Mario A1 - Eiroa, Ernesto JO - Physical Review D VL - 59 Y1 - 1999/4/1 SP - 87301 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999PhRvD..59h7301A&db_key=AST&high=42a068d47530158 N2 - In this paper we improve the results of Sec. VI of a previous paper [M. Castagnino, Phys. Rev. D 57, 750 (1998)] by considering that the main source of entropy production is the photospheres of the stars. ER - TY - Journal T1 - Spherical Shell Dynamics A1 - Aquilano, R. O. A1 - Castagnino, M. A. A1 - Neira, L. P. JO - Astronomical and Astrophysical Transactions VL - 17 Y1 - 1998/1/1 SP - 1 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AT...17....1A&db_key=AST&high=42a068d47530158 N2 - Not Available ER - TY - Journal T1 - Thin Spherically Radiating Shells and Astronomical Collapsed Objects A1 - Aquilano, Roberto JO - General Relativity and Gravitation VL - 29 Y1 - 1997/3/1 SP - 271 EP - 274 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997GReGr..29..271A&db_key=AST&high=42a068d47530158 N2 - Using the shell formalism, relativistic effects could eventually be detected in astronomical collapsed objects. ER - TY - Journal T1 - The Lack of Thermical Equilibrium as a Consequence on the Universe Expansion A1 - Aquilano, Roberto A1 - Castagnino, Mario JO - Astrophysics and Space Science VL - 238 Y1 - 1996/4/1 SP - 159 EP - 167 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996Ap%26SS.238..159A&db_key=AST&high=42a068d47530158 N2 - Not Available ER - TY - Journal T1 - On the Dynamical Equation of a Spherical Radiating Shell A1 - Aquilano, R. O. JO - Astrophysics and Space Science VL - 226 Y1 - 1995/4/1 SP - 173 EP - 186 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Ap%26SS.226..173A&db_key=AST&high=42a068d47530158 N2 - Not Available ER - TY - Journal T1 - Luminosity Profiles and the Contraction of Radiating Spheres in General Relativity A1 - Aquilano, R. A1 - Barreto, W. A1 - Nunez, L. A. JO - Astrophysics and Space Science VL - 225 Y1 - 1995/3/1 SP - 167 EP - 181 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Ap%26SS.225..167A&db_key=AST&high=42a068d47530158 N2 - Not Available ER - TY - Journal T1 - A comparison of the SAO-Hipparcos reference frames A1 - Arias, E. F. A1 - Cionco, R. G. A1 - Orellana, R. B. A1 - Vucetich, H. JO - Astronomy and Astrophysics VL - 359 Y1 - 2000/7/1 SP - 1195 EP - 1200 KW - ASTROMETRY/ REFERENCE SYSTEMS/ CATALOGS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...359.1195A&db_key=AST&high=42a068d47532658 N2 - The reference systems defined by the SAO and Hipparcos catalogues are compared using vector spherical harmonic analysis. The differences between astrometric data in both catalogues have been grouped into different data sets and separate harmonic analysis performed on them. The Fourier coefficients yield estimates of systematic errors in SAO catalogue. ER - TY - Journal T1 - The extragalactic reference system of the International Earth Rotation Service, ICRS. A1 - Arias, E. F. A1 - Charlot, P. A1 - Feissel, M. A1 - Lestrade, J.-F. JO - Astronomy and Astrophysics VL - 303 Y1 - 1995/11/1 SP - 604 EP - 608 KW - REFERENCE SYSTEMS/ ASTROMETRY/ QUASARS:GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...303..604A&db_key=AST&high=42a068d47532658 N2 - The celestial reference system of the International Earth Rotation Service (IERS), ICRS, was recommended to the International Astronomical Union (IAU) for adoption as the conventional system, under the name of International Celestial Reference System, by the IAU working group on reference frames. This system agrees with the decisions taken by IAU in 1991 and it is consistent with the FK5 system at J2000.0. It is maintained on the basis of high-accuracy observations of extragalactic radio sources by very long baseline interferometry (VLBI). The maintenance algorithm ensures stable directions of its axes within +/-20 microarcseconds. The typical accuracy of the source coordinates is +/-300 microarcseconds. ICRS is accessible directly by the observation of extragalactic objects and indirectly through the major reference frames attached to the Galaxy, the Solar System and the Earth. ER - TY - Journal T1 - The massive double-lined O-type binary HD 165052 A1 - Arias, J. I. A1 - Morrell, N. I. A1 - Barbá, R. H. A1 - Bosch, G. L. A1 - Grosso, M. A1 - Corcoran, M. JO - Monthly Notices of the Royal Astronomical Society VL - 333 Y1 - 2002/6/1 SP - 202 EP - 210 KW - binaries: general; stars: early-type; stars: individual: HD 165052; X-rays: stars UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.333..202A&db_key=AST&high=42a068d47502375 N2 - We present a new optical spectroscopic study of the O-type binary HD 165052 based on high- and intermediate-resolution CCD observations. We re-investigated the spectral classification of the binary components, obtaining spectral types of O6.5V and O7.5V for the primary and secondary, respectively, finding that both stars display weak CIIIlambda5696 emission in their spectra. We also determined a radial-velocity orbit for HD 165052 with a period of 2.95510+/-0.00001d, and semi-amplitudes of 94.8 and 104.7+/-0.5kms^-1, resulting in a mass ratio Q=0.9. From a comparison with previous radial-velocity determinations, we found evidence of apsidal motion in the system. Several signatures of wind-wind collision, such as phase-locked variability of the X-ray flux and the Struve-Sahade effect, are also considered. It was also found that the reddening in the region should be normal, in contrast with previous determinations. ER - TY - Journal T1 - The circumstellar environment of the star V923 Aquilae A1 - Arias, M. L. A1 - Cidale, L. S. A1 - Ringuelet, A. E. JO - Astronomy and Astrophysics VL - 417 Y1 - 2004/4/1 SP - 679 EP - 688 KW - stars: emission-line/ Be/ stars: circumstellar matter UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...417..679A&db_key=AST&high=42a068d47503353 N2 - V923 Aquilae is a Be shell star that displays emission in Halpha, cyclic V/R variations and variations in the intensity of the near infrared continuum. The star presents radial velocity variations arising from a superposition of a long-term cycle and an orbital motion with a period of 214.756 days (Koubský et al. \cite{koub}). To investigate the physical properties and the geometry of the circumstellar envelope of this star, we have analysed its spectra in the UV and visual range. We have selected Fe II lines to derive temperatures and location of the line-forming regions. Our results indicate that the dimensions of the circumstellar envelope vary with time and this variation correlates with the orbital period of 214.75 days. On the other hand, we determined a period of 6.8 years for V/R cyclic variations in Halpha. This period is in accordance with the long-term cycle in the radial velocity and U band photometric observations. We suggest that the V/R variability in the Halpha line is linked to the behavior of the subsonic wind structure. ER - TY - Journal T1 - A ¹²CO (J = 1 -> 0) study towards the Ara OB1 region A1 - Arnal, E. M. A1 - May, J. A1 - Romero, G. A. JO - Astronomy and Astrophysics VL - 412 Y1 - 2003/12/1 SP - 431 EP - 445 KW - H II regions: individual: RCW 108/ ISM: molecules/ open clusters and associations: individual: NGC 6193/ open clusters and associations: individual: Ara OB1/ radio continuum: ISM/ radio lines: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...412..431A&db_key=AST&high=42a068d47505411 N2 - Intermediate angular resolution (HPBW=8\farcm7 ) carbon monoxide (¹²CO J=1->0) line observations towards the OB association Ara OB1 are reported. The molecular line observations cover an area of 2\fdg75 x 3\fdg00 , and disclose a rich and complex distribution of the molecular line emission. The molecular features likely to be associated with the OB-association Ara OB1 span the velocity range from -28 to -20 km s^-1. The most negative radial velocities are observed along NGC 6188 (equiv Rim nebula). This nebula marks the interface between the HII region RCW 108 and the highly absorbing molecular material located westwards of the ionised region. The dominant CO structures, labeled E and F, have a radial velocity of about -23.5 and -21.8 km s^-1, respectively. The former harbours a bright optical knot, the infrared cluster RCW-108 and the strong IRAS source 16362-4845. IRAS point sources are also seen in projection onto ¹²CO concentrations F and H. This may indicate that the star forming process is a widespread phenomenon in this molecular complex. Extended continuum emission, having a high degree of spatial correlation with both the infrared and molecular emission, is observed in the region. We believe that this emission, thermal in nature, arises from the ionised surface layers of the molecular complex. The ionising agents are the high mass stars of NGC 6193, the nucleus of Ara OB1. The total amount of molecular gas related to Ara OB1 is about ~ 1.4x 10⁴ M_sun. ER - TY - Journal T1 - A High-Resolution H I Study of the Interstellar Medium Local to HD 193793 A1 - Arnal, E. Marcelo JO - Astronomical Journal VL - 121 Y1 - 2001/1/1 SP - 413 EP - 425 KW - ISM: Bubbles/ Radio Emission Lines/ Stars: Individual: Henry Draper Number: HD 193793/ Stars: Wolf-Rayet UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121..413A&db_key=AST&high=42a068d47505411 N2 - A 2° field centered at the optical position of the Wolf-Rayet (WR) star HD 193793 (â‰¡ WR 140) was surveyed in the H I 21 cm line and in the 1420 MHz radio continuum, using the Dominion Radio Astrophysical Observatory interferometer. The aim of this observations was to look for evidence of an interaction between the WR star and its local interstellar medium (ISM). Our H I data displays a large oval minimum at a velocity of V_sys~=-12 km s^-1, close to the optical position of HD 193793. We believe this H I void was created by WR 140 and its massive companion (HD 193793 is a member of a well-known binary system). The major axis of the H I void is ~11.5 pc and its axial ratio, the ratio of major to minor axis, is ~1.4. This structure is observable over a velocity range of around 11 km s^-1. The H I minimum appears surrounded by a clumpy shell of H I in emission that has a total mass of neutral hydrogen of M_HI~1300 solar masses. The kinematical distance corresponding to a local standard of rest velocity of -12 km s^-1 is approximately 5.4 kpc, which disagrees with the distance of HD 193793, namely, around 1 kpc. Therefore, it is concluded that the H I bubble was blown in an ISM having nonnegligible peculiar motions. Hipparcos proper-motion measurements indicate that HD 193793 has a tangential velocity of 28+/-3 km s^-1 along the major axis of one of the H I minima detected in the interior of the main H I cavity. To reconcile this motion with the physical size of the H I structure blown by the winds of the binary system, it is concluded that such tangential velocity was acquired by the system a short while ago, namely, ~1.3×10⁵ yr. Maps from the IRAS database show a large-scale IR feature, with good spatial correlation with the H I shell surrounding the main H I void. We believe the emission from the IR shell arises from dust grains heated by the energetic stellar continuum photons emitted by the stellar objects. ER - TY - Journal T1 - A high sensitivity Hi survey of the sky at delta <= -25^o A1 - Arnal, E. M. A1 - Bajaja, E. A1 - Larrarte, J. J. A1 - Morras, R. A1 - Pöppel, W. G. L. JO - Astronomy and Astrophysics Supplement Series VL - 142 Y1 - 2000/2/1 SP - 35 EP - 40 KW - SURVEYS/ ISM: GENERAL/ GALAXY: GENERAL RADIO LINES: ISM/ ISM: CLOUDS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26AS..142...35A&db_key=AST&high=42a068d47505411 N2 - This paper reports on a high sensitivity lambda 21-cm neutral hydrogen survey of the sky south of delta <= -25^o. A total of 50980 positions lying on a galactic coordinate grid with points spaced by (bigtriangleup l, bigtriangleup b) = (0\fdg5/cos b, 0\fdg5), were observed with the 30 m dish of the Instituto Argentino de Radioastronomía (IAR). The angular resolution of the survey is HPBW = 30\arcmin, and the velocity coverage spans the interval -450 km s^-1 to +400 km s^-1 (LSR). The velocity resolution is 1.27 km s^-1 and the final rms noise of the entire database is ~ 0.07 K. The brightness temperature scale is accurate to 5%. ER - TY - Journal T1 - The Interstellar Medium around Galactic WN Stars: WR 2, WR 128, and WR 151 A1 - Arnal, E. M. A1 - Cappa, C. E. A1 - Rizzo, J. R. A1 - Cichowolski, S. JO - Astronomical Journal VL - 118 Y1 - 1999/10/1 SP - 1798 EP - 1805 KW - ISM: BUBBLES/ RADIO EMISSION LINES/ STARS: INDIVIDUAL (HD 6327/ HD 187282/ CX CEPHEI)/ STARS: WOLF-RAYET UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....118.1798A&db_key=AST&high=42a068d47505411 N2 - The neutral hydrogen distribution has been studied in the direction of three Galactic Wolf-Rayet (W-R) stars, using the 100 m Effelsberg radio telescope. Neutral hydrogen voids, regions of low H I emissivity, are observed over a 10-16 km s^-1 velocity range for the stars WR 2 (=HD 6327), WR 128 (=HD 187282), and WR 151 (=CX Cep). These minima are interpreted as the observable 21 cm counterpart of the interstellar bubble created by the powerful winds of W-R stars and their progenitors. The H I cavities are elongated structures having an axial ratio ranging from 1.3 (WR 151) to 2.0 (WR 128). As pointed out in previous studies, the W-R stars are always off-center with respect to either the geometric center of the H I void or the absolute minimum inside the cavity. This offset ranges from 40% to 70% of the H I hole's minor axis. The major axes of these cavities are ~30 pc for both WR 2 and WR 128, and ~50 pc for WR 151. The missing H I mass amounts to 96 M_solar (WR 128), 200 M_solar (WR 2), and 480 M_solar (WR 151). Some of the physical parameters of the ring nebula associated with WR 128, such as its expansion velocity, 80+/-22 km s^-1, radius, 6.3+/-0.2 pc, and characteristic age, (7.4+/-2.4)x10^4 yr, are derived from a simple geometric model that accounts for the discrepancy between the radial velocity of the H I hole and the ring nebula related to WR 128. ER - TY - Journal T1 - The HI distribution in the environment of the WR star HD 50896 A1 - Arnal, E. Marcelo A1 - Cappa, Cristina E. JO - Monthly Notices of the Royal Astronomical Society VL - 279 Y1 - 1996/4/1 SP - 788 EP - 798 KW - STARS: INDIVIDUAL: HD 50896/ STARS: WOLF-RAYET/ ISM: BUBBLES/ RADIO LINES: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996MNRAS.279..788A&db_key=AST&high=42a068d47505411 N2 - The neutral matter distribution from the interstellar medium (ISM) located in the vicinity of the galactic Wolf-Rayet (WR) star HD 50896 has been examined by means of HI 21-cm line observations obtained with both low [half-power beamwidth (HPBW)~=34 arcmin] and intermediate (HPBW~=9 arcmin) angular resolution. The most interesting discovery is a huge ovoidal HI minimum spanning the velocity range +1.5 to +10.0 km s^-1, created, very likely, by the joint action of the progenitor of HD 50896 and the WR itself. Inside this cavity, two minima are clearly discernible. The WR star is offset with respect to either the geometrical centre of the main HI void or the inner HI minima. A physical link between S308, the ring nebula associated with HD 50896, and one of the HI minima is suggested by our data. A kinematical distance of ~1 kpc for HD 50896 is derived based on the radial velocity of the HI cavity. The dual HI minimum geometry observed inside the main HI cavity, a feature also seen in the HI distribution of the ISM located close to other galactic WR stars, may be a consequence of the interaction process itself. The ovoidal shape of the main cavity cannot be explained within the framework of the standard interstellar bubble theory. Elongated bubbles may result when the large-scale galactic magnetic field is taken into account. ER - TY - Journal T1 - Response of a Balloon-Borne Omnidirectional Detector to the Atmospheric Secondary Charged Cosmic Radiation at a Place of 11.5 GV Geomagnetic Cut-Off A1 - Azcárate, I. N. JO - Revista Mexicana de Astronomia y Astrofisica VL - 37 Y1 - 2001/10/1 SP - 159 EP - 164 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001RMxAA..37..159A&db_key=AST&high=42a068d47507318 N2 - An experiment performed with a balloon-borne large plastic scintillator is described. The detector system was transported by a stratospheric balloon, that was launched from Reconquista, Provincia of Santa Fe, Argentina, on February 24, 1992. The geomagnetic cut-off of the site is 11.5 GV. The energy loss spectra of both the atmospheric gamma-radiation (for E_gamma >= 4.15 MeV) and the charged component of the secondary cosmic radiation, were alternatively measured at different altitudes, during the ascent of the balloon, and at ceiling altitude. The atmospheric gamma-ray spectrum was analyzed in an earlier paper (Azcárate 2000). The shape of the energy loss spectrum due to charged radiation can be explained, at least qualitatively, by the computation of the response of the detector to this type of radiation. It is argued that, at ceiling altitude, the observed feature in the spectrum is due mainly to relativistic muons inciding horizontally on the detector. The growth curve for the counting rate below the peak and the intensity of relativistic mu mesons are also obtained. ER - TY - Journal T1 - A Determination of the Atmospheric Gamma-Ray Spectrum between 10 and 100 MeV made at High Geomagnetic Cut-Off A1 - Azcárate, I. N. JO - Revista Mexicana de Astronomia y Astrofisica VL - 36 Y1 - 2000/10/1 SP - 81 EP - 88 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000RMxAA..36...81A&db_key=AST&high=42a068d47507318 N2 - The results of two experiments carried out with a large volume balloon-borne omnidirectional plastic scintillator sensitive to high-energy gamma-radiation are reported here. The two flights were carried out on 18 November 1990 and 24 February 1992, at places of 11.1 and 11.5 GV geomagnetic cut-off rigidities, respectively. For an omnidirectional detector and for energies greater than several MeV, most of the detected photons are secondary gamma-rays produced through interactions of the charged cosmic rays with the atmosphere. To unfold the observed pulse height spectrum and obtain the incident gamma-ray spectrum, the detector response function is calculated numerically with some simplifying assumptions. By using this response function, a differential flux dJ/dE = E^-1.2±0.2 photons cm^-2 s^-1 MeV^-1, averaged over all zenith angles, is estimated for the atmospheric gamma-radiation, at an atmospheric depth of 5 g cm^-2, in the 10-100 MeV energy range. This flux turns out to be compatible with other observations made with different types of detectors and at different geomagnetic cut-offs. ER - TY - Journal T1 - H166a Emission as a Tracer of the Warped Ionized Gas Layer in the Northern Galaxy A1 - Azcarate, I. N. A1 - Cersosimo, J. C. A1 - Wilkes, L. M. A1 - Cordero, Y. A. JO - Astrophysics and Space Science VL - 253 Y1 - 1997/1/1 SP - 313 EP - 323 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997Ap%26SS.253..313A&db_key=AST&high=42a068d47507318 N2 - Not Available ER - TY - Journal T1 - Behaviour of a Lead Collimator for a Gamma-Ray Telescope Exposed to Gamma Radiation in the Energy Range 1-100 MeV A1 - Azcárate, I. N. A1 - Mugherli, V. J. JO - Revista Mexicana de Astronomia y Astrofisica VL - 32 Y1 - 1996/10/1 SP - 135 EP - 142 KW - COLLIMATORS/ GAMMA RAY TELESCOPES/ ENERGY SPECTRA/ ATMOSPHERIC EFFECTS/ GAMMA RAYS/ MONTE CARLO METHOD/ ELECTROMAGNETIC INTERACTIONS/ RADIOACTIVITY/ NUCLEAR INTERACTIONS/ COMPUTATION/ CAPTURE EFFECT UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996RMxAA..32..135A&db_key=AST&high=42a068d47507318 N2 - The Monte Carlo method is applied to study the transmission of a lead collimator 3 cm thick to gamma radiation in the energy range 1-100 MeV, which was part of a gamma-ray telescope. The computation gives the continuum spectrum and the 511 keV line intensity emerging from the inner face of the collimator as the result of the electromagnetic interactions occurring inside it. We also discuss the resulting background from the decay of the radioactive nuclei generated by the nuclear interactions (spallation) of cosmic rays, and neutron capture in lead. The overall results show that the induced instrumental background does not significantly reduce the detector sensitivity as compared to that expected of an ideally clean collimator. ER - TY - Journal T1 - Radio Recombination Lines from a Thermal Spur Associated with the Region S54: A Model to Explain the Observational Results A1 - Azcarate, I. N. A1 - Cersosimo, J. C. JO - Astrophysics and Space Science VL - 235 Y1 - 1996/1/1 SP - 141 EP - 147 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996Ap%26SS.235..141A&db_key=AST&high=42a068d47507318 N2 - Not Available ER - TY - Journal T1 - Research note: beta and alpha recombination lines from a region around the Galactic Center. A1 - Azcarate, I. N. A1 - Cersosimo, J. C. JO - Revista Mexicana de Astronomia y Astrofisica VL - 31 Y1 - 1995/4/1 SP - 11 EP - 13 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995RMxAA..31...11A&db_key=AST&high=42a068d47507318 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995RMxAA..31...11A&db_key=AST ER - TY - Journal T1 - Spectroscopic observations of southern nearby galaxies. I. NGC 2442 A1 - Bajaja, E. A1 - Agüero, E. A1 - Paolantonio, S. JO - Astronomy and Astrophysics Supplement Series VL - 136 Y1 - 1999/4/1 SP - 179 EP - 187 KW - GALAXIES: NGC 2442/ KINEMATICS AND DYNAMICS/ NUCLEI/ ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26AS..136..179B&db_key=AST&high=42a068d47509185 N2 - The galaxy NGC 2442 was observed with a REOSC spectrograph, installed in the 2.15 m CASLEO telescope, in order to derive galactic parameters from the observed optical lines and to compare them with the results of radioastronomical observations made in the continuum, at 843 MHz, with the MOST and in the CO lines with the SEST telescope. Recent publications allowed us to extend the comparison to results from interferometric observations of Halpha and H I 21 cm lines and of the continuum at 1415 MHz. The long slit observations were made placing the 5farcm 8 slit at six different positions on the optical image of the galaxy. The emission line intensity ratios at the nuclear region indicate that NGC 2442 is a LINER. The electron temperature and volume density are T_e ~ 14 000 K and N_e ~ 530 cm(-3) , respectively. In contrast, a spectrum of a region 87arcsec to the NE shows the typical characteristics of a H Ii region. In this case T_e ~ 6,500 K and N_e ~ 10 cm(-3) . Good correlations between the distributions of intensities, velocity fields and rotation curves have been found for the optical and radio lines. It is shown that the three intensity peaks along the line at PA = 40degr were not resolved by the observations at radio frequencies. The steep central rotation curve seen in CO has been confirmed and improved showing the existence of a disc or a ring, with a radius of 12.5 arcsec, rotating at 216/sin(i) km s(-1). Two velocity components in three optical spectra obtained in the nuclear region, have been related to two small Halpha regions close to the nucleus and to the central ring. Asymmetries in the distributions of the emitting sources and irregularities in their velocity fields indicate the need of modelling the galaxy before any dynamical study is attempted. Based on observations made in the Complejo Astronomico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina and the National Universities of La Plata, Cordoba and San Juan. ER - TY - Journal T1 - Observations of CO lines in southern spiral galaxies. A1 - Bajaja, E. A1 - Wielebinski, R. A1 - Reuter, H.-P. A1 - Harnett, J. I. A1 - Hummel, E. JO - Astronomy and Astrophysics Supplement Series VL - 114 Y1 - 1995/11/1 SP - 147 KW - GALAXIES: ISM/ SPIRAL/ RADIO LINES: GALAXIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26AS..114..147B&db_key=AST&high=42a068d47509185 N2 - Six southern spiral galaxies, with diameters between 5' and 8', were mapped with the SEST in the ^12^CO(1-0) line. CO emission was detected in five of the galaxies. The 43" beam of the SEST, at 115GHz, was small enough for determining the general distribution of the gas, which is centrally peaked in all the cases, and the velocity field from which we could derive the major axis position angle and the rotation curve. The latter is, in general, very steep at the centre and quite flat after the turn-over point. It was used to estimate the total mass of the galaxy up to the farthest measured point. The gas mass was estimated from the CO and H I global velocity profiles. On three of the galaxies the ^12^CO(2-1) and ^13^CO(1-0) lines were also observed on their centres, the first one on a 10" grid, covering a region of 20"x20", and the second on one point towards the centre. The average ratio between the intensities of the ^12^CO(2-1) and ^12^CO(1-0) spectra is 1.3 in the three cases. The detections of the ^13^CO(1-0) were only marginal. A good correlation has been found between the CO and the continuum emission at 843MHz. ER - TY - Journal T1 - Active Star Formation in the N11B Nebula in the Large Magellanic Cloud: A Sequential Star Formation Scenario Confirmed A1 - Barbá, Rodolfo H. A1 - Rubio, Mónica A1 - Roth, Miguel R. A1 - García, Jorge JO - Astronomical Journal VL - 125 Y1 - 2003/4/1 SP - 1940 EP - 1957 KW - ISM: H II Regions/ Infrared Radiation/ ISM: Individual: Alphanumeric: N11/ ISM: Molecules/ Galaxies: Magellanic Clouds/ Stars: Formation UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....125.1940B&db_key=AST&high=42a068d47510777 N2 - The second largest H II region in the Large Magellanic Cloud, N11B has been surveyed in the near-IR. We present JHK_s images of the N11B nebula. These images are combined with CO (1-->0) emission-line data and with archival New Technology Telescope and Hubble Space Telescope WFPC2 optical images to address the star formation activity of the region. IR photometry of all the IR sources detected is given. We confirm that a second generation of stars is currently forming in the N11B region. Our IR images show the presence of several bright IR sources that appear to be located toward the molecular cloud as seen from the CO emission in the area. Several of these sources show IR colors with young stellar object characteristics, and they are prime candidates to be intermediate-mass Herbig Ae/Be stars. For the first time, an extragalactic methanol maser is directly associated with IR sources embedded in a molecular core. Two IR sources are found at 2" (0.5 pc) of the methanol maser reported position. Additionally, we present the association of the N11A compact H II region to the molecular gas, where we find that the young massive O stars have eroded a cavity in the parental molecular cloud, typical of a champagne flow. The N11 region turns out to be a very good laboratory for studying the interaction of winds, UV radiation, and molecular gas. Several photodissociation regions are found. Based in part on observations with the NASA/ESA Hubble Space Telescope obtained from the archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. ER - TY - Journal T1 - Sudden Luminous Blue Variable--Like Behavior of the Wolf-Rayet Binary System HD 5980 in the Small Magellanic Cloud A1 - Barba, Rodolfo H. A1 - Niemela, Virpi S. A1 - Baume, Gustavo A1 - Vazquez, R. A. JO - Astrophysical Journal VL - 446 Y1 - 1995/6/1 SP - L23 KW - STARS: BINARIES: CLOSE/ STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 60435/ STARS: VARIABLES: OTHER LUMINOUS BLUE VARIABLES/ STARS: WOLF-RAYET UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ApJ...446L..23B&db_key=AST&high=42a068d47510777 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446L..23B&db_key=AST ER - TY - Journal T1 - Globular cluster candidates within the Fornax Cluster: Intracluster globulars? A1 - Bassino, L. P. A1 - Cellone, S. A. A1 - Forte, J. C. A1 - Dirsch, B. JO - Astronomy and Astrophysics VL - 399 Y1 - 2003/2/1 SP - 489 EP - 496 KW - Galaxy: globular clusters: general/ galaxies: star clusters/ galaxies: dwarf/ galaxies: clusters: individual Fornax UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...399..489B&db_key=AST&high=42a068d47513039 N2 - We present the results of a search for globular clusters in the surroundings of 15 low surface brightness dwarf galaxies belonging to the Fornax Cluster, which was carried out on CCD images obtained with the C and T_1 filters of the Washington photometric system. The globular cluster candidates show an extended and probably bimodal (C-T_1) color distribution, which is inconsistent with the presence of a single population of metal-poor clusters detected in several dwarf galaxies. The surface number density of these candidates shows no concentration towards the respective dwarf galaxies, in whose outskirts they have been identified. On the contrary, if we split the candidates in two groups according to their projected distances to the center of the Fornax Cluster, those located closer to the center show a higher projected density than those located farther from it. These results suggest that the potential globular clusters might not be bound to the dwarf galaxies. Alternatively, these globulars could form part of the very peripheral regions of NGC 1399 (the central galaxy of the Fornax Cluster) or even belong to the intracluster medium. Based on observations obtained at Cerro Tololo Inter-American Observatory, NOAO, which is operated by AURA, Inc., under cooperative agreement with the National Science Foundation. ER - TY - Journal T1 - Erratum: CCD photometry in the region of NGC 6994: The remains of an old open cluster A1 - Bassino, L. P. A1 - Waldhausen, S. A1 - Martínez, R. E. JO - Astronomy and Astrophysics VL - 356 Y1 - 2000/4/1 SP - 389 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...356..389B&db_key=AST&high=42a068d47513039 N2 - In the caption of Fig.~1, the correct orientation of the CCD image is: South is up and east is to the left. ER - TY - Journal T1 - CCD photometry in the region of NGC 6994: The remains of an old open cluster A1 - Bassino, L. P. A1 - Waldhausen, S. A1 - Martínez, R. E. JO - Astronomy and Astrophysics VL - 355 Y1 - 2000/3/1 SP - 138 EP - 144 KW - OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 6994/ TECHNIQUES: PHOTOMETRIC UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...355..138B&db_key=AST&high=42a068d47513039 N2 - We present the results of BV(RI)_KC CCD photometry down to V=21 mag in the region of NGC 6994. To our knowledge, no photometry has previously been reported for this object and we find evidences that it is a poor and sparse old open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the 3 arcmin originally assigned to it. We obtain a color excess E_B-V = 0.07 +/- 0.02 mag by means of the BVI_C technique. Based on the theoretical isochrones from \cite{van85} that are in better agreement with our data, we estimate for this cluster a distance from the Sun of 620 pc (V₀-M_V = 9 +/- 0.25 mag) and an age lying within the range of 2 - 3 Gyr, adopting solar metallicity. Thus, the corresponding cluster's Galactocentric distance is 8.1 kpc and is placed at about 350 pc below the Galactic plane. According to these results, NGC 6994 belongs to the old open cluster population located in the outer disk and at large distances from the Galactic plane, and must have suffered significant individual dynamical evolution, resulting in mass segregation and evaporation of low mass stars. Table~1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - Dwarf Galaxies Captured by Giants in Clusters A1 - Bassino, Lilia P. A1 - Muzzio, Juan C. A1 - Pérez, Josefa JO - Celestial Mechanics and Dynamical Astronomy VL - 72 Y1 - 1999/1/1 SP - 157 EP - 168 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999CeMDA..72..157B&db_key=AST&high=42a068d47513039 N2 - Not Available ER - TY - Journal T1 - Dwarf galaxies captured by giants in clusters A1 - Bassino, Lilia P. A1 - Muzzio, Juan C. A1 - Pérez, Josefa JO - Celestial Mechanics and Dynamical Astronomy VL - 72 Y1 - 1998/1/1 SP - 157 EP - 168 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998CeMDA..72..157B&db_key=AST&high=42a068d47513039 N2 - We performed simple numerical simulations to investigate the capture of dwarf galaxies by larger ones in the environment of a cluster of galaxies. The number of captures is small compared to the total number of dwarfs, but it is significant because these galaxies are the most abundant members of galaxy clusters. Our models show that, having a more massive central galaxy or a less massive background halo in the cluster, increases the number of captures. A high proportion of the orbits of the captured dwarfs are very eccentric. ER - TY - Journal T1 - Is M54 the nucleus of the Sagittarius galaxy? A1 - Bassino, L. P. A1 - Muzzio, J. C. JO - The Observatory VL - 115 Y1 - 1995/10/1 SP - 256 EP - 257 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Obs...115..256B&db_key=AST&high=42a068d47513039 N2 - Not Available ER - TY - Journal T1 - NGC 2580 and NGC 2588. Two open clusters in the Third Galactic Quadrant A1 - Baume, G. A1 - Moitinho, A. A1 - Giorgi, E. E. A1 - Carraro, G. A1 - Vázquez, R. A. JO - Astronomy and Astrophysics VL - 417 Y1 - 2004/4/1 SP - 961 EP - 972 KW - Galaxy: open clusters and associations: individual: NGC 2580/ NGC 2588/ Galaxy: open clusters and associations: general UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...417..961B&db_key=AST&high=42a068d47514318 N2 - We present CCD broad band photometric observations in the fields of the Third Galactic Quadrant open clusters NGC 2580 and NGC 2588 (V(I)_C and UBV(RI)_C respectively). From the analysis of our data we found that NGC 2580 is located at a distance of about 4 kpc and its age is close to 160 Myr. As for NGC 2588, it is placed at about 5 kpc from the Sun and is 450 Myr old. This means that NGC 2588 belongs to the extension of the Perseus arm, whereas NGC 2580 is closer to the local arm structure. The luminosity functions (LFs) have been constructed for both clusters down to V ~ 20 together with their initial mass functions (IMFs) for stars with masses above M ~ 1-1.5 M_âŠ™. The IMF slopes for the most massive bins yielded values of x â‰ˆ 1.3 for NGC 2580 and x â‰ˆ 2 for NGC 2588. In the case of this latter cluster we found evidence of a core-corona structure produced probably by dynamical effect. In the main sequences of both clusters we detected gaps, which we suggest could be real features. Based on observations c ollected at ESO, CASLEO and CTIO. Table 3 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/961 ER - TY - Journal T1 - A study of the two northern open clusters NGC 1582 and NGC 1663 A1 - Baume, G. A1 - Villanova, S. A1 - Carraro, G. JO - Astronomy and Astrophysics VL - 407 Y1 - 2003/8/1 SP - 527 EP - 539 KW - Galaxy: open clusters and associations: individual: NGC 1582 and NGC 1663/ open clusters and associations: general UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...407..527B&db_key=AST&high=42a068d47514318 N2 - We present CCD UBV(I)_C observations obtained in the field of the previously unstudied northern open clusters NGC 1582 and NGC 1663. For the former, we also provide high-resolution spectra of the brightest stars and complement our data with Two-Micron All-Sky-Survey (2MASS) near-infrared photometry and with astrometric data from the Tycho-2 catalog. From the analysis of all these data, we argue that NGC 1582 is a very poor, quite large and heavily contaminated open cluster. It turns out to have a reddening E_B-V = 0.35 +/- 0.03, to be situated 1100 +/- 100 pc from the Sun and to have an age of 300 +/- 100 Myr. On the other hand, we were not able to unambiguously clarify the nature of NGC 1663. By assuming it is a real cluster and from the analysis of its photometric diagrams, we found a color excess value E_B-V = 0.20, an intermediate age value ( ~ 2000 Myr) and a distance of about 700 pc. The distribution of the stars in the region however suggests we are probably facing an open cluster remnant. As an additional result, we obtained aperture photometry of three previously unclassified galaxies placed in the field of NGC 1663 and performed a preliminary morphological classification of them. Based on observations carried out at Mt Ekar, Asiago, Italy. Data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/527 ER - TY - Journal T1 - Photometric study of the young open cluster NGC 3293 A1 - Baume, G. A1 - Vázquez, R. A. A1 - Carraro, G. A1 - Feinstein, A. JO - Astronomy and Astrophysics VL - 402 Y1 - 2003/5/1 SP - 549 EP - 564 KW - Galaxy: open clusters and associations: individual: NGC 3293/ stars: imaging/ stars: luminosity function/ mass function UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...402..549B&db_key=AST&high=42a068d47514318 N2 - Deep and extensive CCD photometric observations at UBV(RI)_CH_alpha were carried out in the area of the open cluster NGC 3293. The new data set allows to see the entire cluster sequence down to M_V ~ +4.5, revealing that stars with M_V < -2 are evolving off the main sequence; stars with -2 < M_V < +2 are located on the main sequence and stars with M_V > +2 are placed above it. According to our analysis, the cluster distance is d = 2750 +/- 250 pc (V₀-M_V = 12.2 +/- 0.2) and its nuclear age is 8 +/- 1 Myr. NGC 3293 contains an important fraction of pre-main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to 2.5 cal M_sun and a mean contraction age of 10 Myr. This last value does not differ too much from the nuclear age estimate. If we take into account the many factors that may affect the PMS star positions on the colour-magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Using the H_alpha data, we detected nineteen stars with signs of H_alpha emission in the region of NGC 3293, another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope of x = 1.2 +/- 0.2, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters. Based on observations collected at UTSO, ESO (Dutch 0.9 m telescope) and CASLEO. The CCD and data acquisition system at CASLEO has been partly financed by R.M. Rich through U.S. NSF Grant AST-90-15827. Full Table 1 is only available in electronic form at the CDS via an anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/549 ER - TY - Journal T1 - UBVI imaging photometry of NGC 6231 A1 - Baume, G. A1 - Vázquez, R. A. A1 - Feinstein, A. JO - Astronomy and Astrophysics Supplement Series VL - 137 Y1 - 1999/6/1 SP - 233 EP - 244 KW - CLUSTER: OPEN/ INDIVIDUAL: NGC 6231/ STARS: LUMINOSITY FUNCTION/ MASS FUNCTION/ HR DIAGRAM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26AS..137..233B&db_key=AST&high=42a068d47514318 N2 - CCD UBVI photometry in the field of the open cluster NGC 6231 was obtained for 1060 stars down to V~ 19 mag. Memberships, reddening, distance and age of this cluster were investigated. Its lower sequence displays a notorious bend at V~ 13.5 mag followed by a high number of faint stars showing a large magnitude spread at constant colour. This distribution of stars does not seem to be produced by a mere accumulation of field stars seen in the direction of the cluster but by a real star excess in the zone. The evidence suggests these stars are serious candidates to be cluster members caught in their way towards the ZAMS. Fitting them with pre main sequence isochrones an age spread of about 10 Myr is obtained. The luminosity and mass functions were found to be flat for -7.5 < M_V < 1.5 and from 3 to 80 {cal M_sun} respectively. Based on observations collected at the University of Toronto Southern Observatory, Las Campanas, Chile. Table 1 is available only in electronic form at the CDS via anonymous ftp (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - The Parabolic Three-Body Problem A1 - Beaugé, C. JO - Celestial Mechanics and Dynamical Astronomy VL - 88 Y1 - 2004/1/1 SP - 51 EP - 68 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004CeMDA..88...51B&db_key=AST&high=42a068d47515959 N2 - In this communication we present an analytical model for the restricted three-body problem, in the case where the perturber is in a parabolic orbit with respect to the central mass. The equations of motion are derived explicitly using the so-called Global Expansion of the disturbing function, and are valid for any eccentricity of the massless body, as well as in the case where both secondary masses have crossing orbits. Integrating the equations of motion over the complete passage of the perturber through the system, we are then able to construct a first-order algebraic mapping for the change in semimajor axis, eccentricity and inclination of the perturbed body. Comparisons with numerical solutions of the exact equations show that the map yields precise results, as long as the minimum distance between both bodies is not too small. Finally, we discuss several possible applications of this model, including the evolution of asteroidal satellites due to background bodies, and simulations of passing stars on extra-solar planets. ER - TY - Journal T1 - Extrasolar Planets in Mean-Motion Resonance: Apses Alignment and Asymmetric Stationary Solutions A1 - Beaugé, C. A1 - Ferraz-Mello, S. A1 - Michtchenko, T. A. JO - Astrophysical Journal VL - 593 Y1 - 2003/8/1 SP - 1124 EP - 1133 KW - Celestial Mechanics/ Stars: Planetary Systems UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...593.1124B&db_key=AST&high=42a068d47515959 N2 - In recent years several pairs of extrasolar planets have been discovered in the vicinity of mean-motion commensurabilities. In some cases, such as the GJ 876 system, the planets seem to be trapped in a stationary solution, the system exhibiting a simultaneous libration of the resonant angle theta₁=2lambda₂-lambda₁-varpi₁ and of the relative position of the pericenters. In this paper we analyze the existence and location of these stable solutions, for the 2:1 and 3:1 resonances, as functions of the masses and orbital elements of both planets. This is undertaken via an analytical model for the resonant Hamiltonian function. The results are compared with those of numerical simulations of the exact equations. In the 2:1 commensurability, we show the existence of three principal families of stationary solutions: (1) aligned orbits, in which theta₁ and varpi₁-varpi₂ both librate around zero, (2) antialigned orbits, in which theta₁=0 and the difference in pericenter is 180°, and (3) asymmetric stationary solutions, in which both the resonant angle and varpi₁-varpi₂ are constants with values different from 0° or 180°. Each family exists in a different domain of values of the mass ratio and eccentricities of both planets. Similar results are also found in the 3:1 resonance. We discuss the application of these results to the extrasolar planetary systems and develop a chart of possible planetary orbits with apsidal corotation. We estimate, also, the maximum planetary masses in order for the stationary solutions to be dynamically stable. ER - TY - Journal T1 - Modelling the high-eccentricity planetary three-body problem. Application to the GJ876 planetary system A1 - Beaugé, C. A1 - Michtchenko, T. A. JO - Monthly Notices of the Royal Astronomical Society VL - 341 Y1 - 2003/5/1 SP - 760 EP - 770 KW - methods: analytical/ celestial mechanics/ planets and satellites: general/ planetary systems UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.341..760B&db_key=AST&high=42a068d47515959 N2 - The discovery of extrasolar planets located in the vicinity of mean-motion commensurabilities has opened a new arena for the study of resonance capture and its possible role in the dynamical evolution and long-term stability of planetary systems. Contrary to our own Solar System, many of these planets have highly eccentric orbits (~0.1-0.6), making the use of usual analytical perturbative models very limited. Even so, several attempts have been made to apply classical expansions of the resonant Hamiltonian to these cases, leading to results which are, at best, extrapolations of the low-eccentricity resonant structure, and not necessarily precise. In this paper we present a new analytical expansion for the Hamiltonian of the planetary three-body problem which does not suffer these restrictions, and is even valid for crossing orbits. The only limitation is its applicability to planar motions. The resulting model can be applied to resonant and non-resonant configurations alike. We show examples of this expansion in different resonances and we compare the results with numerical determinations of the exact Hamiltonian. Finally, we apply the developed model to the case of two planets in the 2/1 mean-motion commensurability (such as the Gliese 876 system), and we analyse its periodic orbits and general structure of the resonant phase space at low and high eccentricities. ER - TY - Journal T1 - Effects of Planetary Migration on Natural Satellites of the Outer Planets A1 - Beaugé, C. A1 - Roig, F. A1 - Nesvorný, D. JO - Icarus VL - 158 Y1 - 2002/8/1 SP - 483 EP - 498 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Icar..158..483B&db_key=AST&high=42a068d47515959 N2 - Numerous studies in the past few years have analyzed possible effects of planetary migration on the small bodies of the Solar System (mainly asteroids and KBOs), with the double aim of explaining certain dynamical structures in these systems, as well as placing limits on the magnitude of the radial migration of the planets. Here we undertake a similar aim, only this time concentrating on the dynamical stability of planetary satellites in a migration scenario. However, different from previous works, the strongest perturbations on satellite systems are not due to the secular variation of the semimajor axes of the planets, but from the planetesimals themselves. These perturbations result from close approaches between the planetesimals and satellites. We present results of several numerical simulations of the dynamical evolution of real and fictitious satellite systems around the outer planets, under the effects of multiple passages of a population of planetesimals representing the large-body component of a residual rocky disk. Assuming that this component dominated the total mass of the disk, our results show that the present systems of satellites of Uranus and Neptune do not seem to be compatible with a planetary migration larger than even one quarter that suggested by previous studies, unless these bodies were originated during the late stage of evaporation of the planetesimal disk. For larger variations of the semimajor axes of the planets, most of the satellites would either be ejected from the system or suffer mutual collisions due to excitation in their eccentricities. For the systems of Jupiter and Saturn, these perturbations are not so severe, and even large migrations do not introduce large instabilities. Nevertheless, even a small number of 1000-km planetesimals in the region may introduce significant excitation in the eccentricities and inclinations of satellites. Adequate values of this component may help explain the present dynamical distribution of distant satellites, including the highly peculiar orbit of Nereid. ER - TY - Journal T1 - A Semianalytical Model for the Motion of the Trojan Asteroids: Proper Elements and Families A1 - Beaugé, C. A1 - Roig, F. JO - Icarus VL - 153 Y1 - 2001/10/1 SP - 391 EP - 415 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001Icar..153..391B&db_key=AST&high=42a068d47515959 N2 - In this paper we develop a semianalytical model to describe the long-term motion of Trojan asteroids located in tadpole orbits around the L₄ and L₅ jovian Lagrangian points. The dynamical model is based on the spatial elliptic three-body problem, including the main secular variations of Jupiter's orbit and the direct perturbations of the remaining outer planets. Based on ideas introduced by A. H. Jupp (1969, Astron. J. 74, 35-43), we develop a canonical transformation which allows the transformation of the tadpole librating orbits into circulating orbits. The disturbing function is then explicitly expanded around each libration point by means of a Taylor-Fourier asymmetric expansion. Making use of the property in which the different degrees of freedom in the Trojan problem are well separated with regard to their periods of oscillation, we are able to find approximate action-angle variables combining Hori's method with the theory of adiabatic invariants. This procedure is applied to estimate proper elements for the sample of 533 Trojans with well determined orbits at December 2000. The errors of our semianalytical estimates are about 2-3 times larger than those previously obtained with numerical approaches by other authors. Finally, we use these results to search for asteroidal families among the Trojan swarms. We are able to identify and confirm the existence of most of the families previously detected by Milani (1993, Celest. Mech. Dynam. Astron. 57, 59-94). The families of Menelaus and Epeios, both around L₄, are the most robust candidates to be the by-product of catastrophic disruption of larger asteroids. On the other hand, no significant family is detected around L₅. ER - TY - Journal T1 - A second-order theory for resonance capture in corotation centers A1 - Beauge, C. A1 - Lemaître, A. A1 - Jancart, S. JO - Planetary and Space Science VL - 47 Y1 - 1999/5/1 SP - 643 EP - 652 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999P%26SS...47..643B&db_key=AST&high=42a068d47515959 N2 - In this paper we revisit the analytical determination of the corotation solutions of the restricted planar three-body problem under the effects of a Stokes drag. Previous calculations by different authors, and using different external dissipative forces, have always shown significant quantitative errors of the models with respect to the numerical values. Up to date no concrete explanation has been obtained for this discrepancy. We show that the origin of these errors lies not only in the modelization of the gravitational forces (i.e. disturbing function) but in the averaging process of the variational equations. A second-order averaging is developed based on a Lie transform method ([Kamel, 1969]). With it we can calculate new equilibrium solutions with a greatly improved accuracy. In a second part, this same perturbation method is applied to study the periodic orbits (i.e. limit cycles) which describe the motion of the particles around the averaged corotational solutions. We show how analytical approximations of these cycles can be obtained through the inverse transformation of the averaging process itself. In all cases, we present comparisons with numerical simulations of the exact equations. ER - TY - Journal T1 - On the Motion of Trapped Particles in the Vicinity of Corotation Centers A1 - Beaugé, C. A1 - Lemaître, A. A1 - Jancart, S. JO - Celestial Mechanics and Dynamical Astronomy VL - 73 Y1 - 1999/1/1 SP - 97 EP - 105 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999CeMDA..73...97B&db_key=AST&high=42a068d47515959 N2 - In the present paper we analyse the motion of a massless particle during the capture process in an exterior mean-motion resonance under the effects of an external dissipative force. In particular, we study the orbital evolution from its initial approach to the commensurability up to the final nesting place in the periodic orbit around the equilibrium solution. ER - TY - Journal T1 - On the Effect of Short-Period Terms in Resonance Trapping A1 - Beaugé, C. JO - Celestial Mechanics and Dynamical Astronomy VL - 68 Y1 - 1998/1/1 SP - 283 EP - 303 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998CeMDA..68..283B&db_key=AST&high=42a068d47515959 N2 - Not Available ER - TY - Journal T1 - On a Global Expansion of the Disturbing Function in the Planar Elliptic Restricted Three-Body Problem A1 - Beauge, C. JO - Celestial Mechanics and Dynamical Astronomy VL - 64 Y1 - 1996/1/1 SP - 313 EP - 350 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996CeMDA..64..313B&db_key=AST&high=42a068d47515959 N2 - Not Available ER - TY - Journal T1 - Radio observations of HD 93129A: The earliest O star with the highest mass loss? A1 - Benaglia, P. A1 - Koribalski, B. JO - Astronomy and Astrophysics VL - 416 Y1 - 2004/3/1 SP - 171 EP - 178 KW - stars: individual: HD 93129A/ HD 93129B/ HD 93128/ stars: mass-loss/ stars: winds/ outflows/ radio continuum: stars UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...416..171B&db_key=AST&high=42a068d47517524 N2 - We present the results of radio continuum observations towards the open cluster Tr 14, where our main targets are the early-type O stars HD 93129A/B and HD 93128. The observations were carried out at 3 cm (8.64 GHz) and 6 cm (4.80 GHz) with the Australia Telescope Compact Array. Only HD 93129A (type O2 If*) was detected; we measure flux densities of S₃ cm = 2.0 ± 0.2 mJy and S₆ cm = 4.1 ± 0.4 mJy. The resulting spectral index of alpha = -1.2 ± 0.3 (S_nu âˆ nu^alpha) indicates predominantly non-thermal emission, suggesting HD 93129A may be a binary system. We propose that the observed 3 cm radio emission is mostly coming from the non-thermal wind collision region of a binary, and, to a lesser extent, from the thermal winds of the primary and secondary stars in HD 93129A. At a stellar distance of 2.8 kpc, we derive a mass-loss rate M_âŠ™ = 5.1 × 10^-5 M_âŠ™ yr^-1, assuming the thermal fraction of the 3 cm emission is ~0.5. ER - TY - Journal T1 - Gamma-ray emission from Wolf-Rayet binaries A1 - Benaglia, P. A1 - Romero, G. E. JO - Astronomy and Astrophysics VL - 399 Y1 - 2003/3/1 SP - 1121 EP - 1134 KW - stars: early-type/ stars: binaries: general/ stars: winds/ outflows/ radio continuum: stars/ gamma-rays: observations/ gamma-rays: theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...399.1121B&db_key=AST&high=42a068d47517524 N2 - In the colliding wind region of early-type binaries, electrons can be accelerated up to relativistic energies displaying power-law spectra, as demonstrated by the detection of non-thermal radio emission from several WR+OB systems. The particle acceleration region, located between the stars, is exposed to strong photon fields in such a way that inverse Compton cooling of the electrons could result in a substantial high-energy non-thermal flux. In particular cases, the ratio of the energy densities of magnetic to photon fields in the colliding wind region will determine whether a given source can produce or not significant gamma-ray emission. We present here a study of the binaries WR 140, WR 146, and WR 147 in the light of recent radio and gamma-ray observations. We show that with reasonable assumptions for the magnetic field strength WR 140 can produce the gamma-ray flux from the EGRET source 3EG J2022+4317. WR 146 and WR 147 are below the detection threshold, but new and forthcoming instruments like INTEGRAL and GLAST might detect non-thermal emission from them. ER - TY - Journal T1 - Mass loss rate determination of southern OB stars A1 - Benaglia, P. A1 - Cappa, C. E. A1 - Koribalski, B. S. JO - Astronomy and Astrophysics VL - 372 Y1 - 2001/6/1 SP - 952 EP - 962 KW - STARS: EARLY-TYPE/ STARS: MASS LOSS/ STARS: WINDS/ OUTFLOWS/ RADIO CONTINUUM: STARS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...372..952B&db_key=AST&high=42a068d47517524 N2 - A sample of OB stars (eleven Of, one O and one B supergiant) has been surveyed with the Australia Telescope Compact Array at 4.8 and 8.64 GHz with a resolution of ~ 2 arcsec-4 arcsec. Five stars were detected; three of them have negative spectral indices, consistent with non-thermal emission, and two have positive indices. The thermal radiation from HD 150135 and HD 163181 can be explained as coming from an optically thick ionized stellar wind. The non-thermal radiation from CD-47^deg 4551, HD 124314 and HD 150136 possibly comes from strong shocks in the wind itself and/or in the wind colliding region if the stars have a massive early-type companion. The percentage of non-thermal emitters among detected O stars has increased up to ~ 50%. The Of star HD 124314 clearly shows flux density variations. Mass loss rates (or upper limits) were derived for all the observed stars and the results compared with non-radio measurements and theoretical predictions. ER - TY - Journal T1 - Can the gamma-ray source 3EG J2033+4118 be produced by the stellar system Cygnus OB2 No. 5? A1 - Benaglia, P. A1 - Romero, G. E. A1 - Stevens, I. R. A1 - Torres, D. F. JO - Astronomy and Astrophysics VL - 366 Y1 - 2001/2/1 SP - 605 EP - 611 KW - GAMMA-RAYS: THEORY/ GAMMA-RAYS: OBSERVATIONS/ STARS: EARLY-TYPE/ STARS: WINDS/ OUTFLOWS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...366..605B&db_key=AST&high=42a068d47517524 N2 - We discuss the possibility that the stellar system Cyg OB2 No. 5 can be a gamma-ray source in the light of recent EGRET and radio data. This system is formed by an O7 Ia + Ofpe/WN9 contact binary. A third star, probably a B0 V star also associated with the system, is located at ~ 1700 AU from the primary. We estimate the expected gamma-ray luminosity from the colliding winds region, the terminal shock of the wind, and the unstable zone at the base of the wind, and conclude that, under very reasonable assumptions, Cyg OB2 No. 5 can generate about a half of the gamma-ray flux detected from the positionally coincident source 3EG J2033+4118. We suggest, then, that other O stars belonging to the association, also placed within the 95% probability EGRET location contour, could contribute to the observed gamma-ray flux. ER - TY - Journal T1 - Possible wind blown bubbles associated with five Of stars A1 - Benaglia, P. A1 - Cappa, C. E. JO - Astronomy and Astrophysics VL - 346 Y1 - 1999/6/1 SP - 979 EP - 989 KW - STARS: INDIVIDUAL: HD 152386/ HD 153919/ HD 91572/ HD 91824/ HD 94963/ ISM: BUBBLES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...346..979B&db_key=AST&high=42a068d47517524 N2 - Four fields of ~ 5(deg) x 4(deg) have been surveyed using the Hi -21 cm line (hpbw = 0 fdg 5) in searching for Hi interstellar bubbles in the environs of several Of stars. The analysis of the data disclosed four bubble candidates, three with almost complete envelopes. Their dimensions are ~ 40 pc and their expansion velocities around 10 km s(-1) . For each structure swept-up masses (1000 to 8800 M_sun), original ambient gas densities ( <~ 0.6 cm(-3) ), dynamical ages ( ~ 2 Myr) and kinetic energies (<~ 2 x 10(49) erg) were derived. The origin of the Hi shells is discussed, taking into account their kinematics, energy, age and the emission at other wavelengths. As in the case of several WR Hi shells, the O strong stellar winds would be the main agents blowing the Hi bubbles. ER - TY - Journal T1 - The formation of a helium white dwarf in a close binary system with diffusion A1 - Benvenuto, O. G. A1 - De Vito, M. A. JO - Monthly Notices of the Royal Astronomical Society VL - 352 Y1 - 2004/7/1 SP - 249 EP - 257 KW - binaries: general/ stars: evolution/ stars: interiors UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.352..249B&db_key=AST&high=42a068d47519812 N2 - We study the evolution of a system composed of a 1.4-M_solar neutron star and a normal, solar composition star of 2 M_solar in orbit with a period of 1 d. Calculations were performed employing the binary HYDRO code presented by Benvenuto & De Vito that handle the mass transfer rate in a fully implicit way. We then included the main standard physical ingredients together with the diffusion processes and a proper outer boundary condition. We have assumed fully non-conservative mass transfer episodes. In order to study the interplay of mass loss episodes and diffusion we considered evolutionary sequences with and without diffusion in which all Roche lobe overflows (RLOFs) produce mass transfer. Another two sequences in which thermonuclearly driven RLOFs were not allowed to drive mass transfer have been computed with and without diffusion. As far as we are aware, this study represents the first binary evolution calculations in which diffusion is considered. The system produces a helium white dwarf of ~0.21 M_solar in an orbit with a period of ~4.3 d for the four cases. We find that mass transfer episodes induced by hydrogen thermonuclear flashes drive a tiny amount of mass transfer. As diffusion produces stronger flashes, the amount of hydrogen-rich matter transferred is slightly higher than in the models without diffusion. We find that diffusion is the main agent in determining the evolutionary time-scale of low-mass white dwarfs even in the presence of mass transfer episodes. ER - TY - Journal T1 - Asteroseismological bound on Gdot/G from pulsating white dwarfs A1 - Benvenuto, Omar G. A1 - García-Berro, Enrique A1 - Isern, Jordi JO - Physical Review D VL - 69 Y1 - 2004/4/1 SP - 82002 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004PhRvD..69h2002B&db_key=AST&high=42a068d47519812 N2 - We study the secular variation of the period of nonradial pulsations of white dwarfs when a temporal dependence of the gravitational constant G is assumed. We consider models that reproduce accurately the main characteristics of the best studied DA (hydrogen-rich atmosphere) white dwarf G117-B15A. For this object it has been possible to measure the secular variation of the main observed period of 215.2 s (=2.3±1.4×10^-15 s^-1) with unprecedented accuracy. Comparing our models with observations we obtain that for Gdot<0 the allowed values are in the range -2.5×10^-10 yr^-1â‰²Gdot/Gâ‰²0, whereas, for Gdot>0, the allowed values are 0â‰²Gdot/Gâ‰²4.0×10^-11 yr^-1 at the 2sigma confidence level, which are comparable to other bounds established by independent methods. We also show that in order to improve this bound significantly an improvement in the precision of the observed change in which is too large to be reached in the foreseeable future is required. ER - TY - Journal T1 - A code for stellar binary evolution and its application to the formation of helium white dwarfs A1 - Benvenuto, O. G. A1 - De Vito, M. A. JO - Monthly Notices of the Royal Astronomical Society VL - 342 Y1 - 2003/6/1 SP - 50 EP - 60 KW - binaries: general/ stars: evolution/ stars: interiors UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.342...50B&db_key=AST&high=42a068d47519812 N2 - We present a numerical code intended for calculating stellar evolution in close binary systems. In doing so, we consider that mass transfer episodes occur when the stellar size overflows the corresponding Roche lobe. In such a situation we equate the radius of the star to the equivalent radius of the Roche lobe. This equation is handled implicitly together with those corresponding to the whole structure of the star. We describe in detail the necessary modifications to the standard Henyey technique for treating the mass-loss rate implicitly together with thin outer-layer integrations. We have applied this code to the calculation of the formation of low-mass, helium white dwarfs in low-mass close binary systems. We find that the global numerical convergence properties are fairly good. In particular, the onset and end of mass transfer episodes are computed automatically. ER - TY - Journal T1 - Addendum: Calculation of the masses of the binary star HD 93205 by application of the theory of apsidal motion A1 - Benvenuto, O. G. A1 - Serenelli, A. M. A1 - Althaus, L. G. A1 - Barbá, R. H. A1 - Morrell, N. I. JO - Monthly Notices of the Royal Astronomical Society VL - 336 Y1 - 2002/11/1 SP - 1056 EP - 1056 KW - binaries: eclipsing/ stars: early-type/ stars: evolution/ stars: fundamental parameters/ stars: individual: HD 93205/ stars: interiors UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.336.1056B&db_key=AST&high=42a068d47519812 N2 - Not Available ER - TY - Journal T1 - On mode trapping in pulsating DA white dwarf stars A1 - Benvenuto, O. G. A1 - Córsico, A. H. A1 - Althaus, L. G. A1 - Serenelli, A. M. JO - Monthly Notices of the Royal Astronomical Society VL - 335 Y1 - 2002/9/1 SP - 480 EP - 486 KW - stars: evolution/ stars: interiors/ stars: oscillations/ white dwarfs UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.335..480B&db_key=AST&high=42a068d47519812 N2 - The effects are explored of time-dependent element diffusion on the mode-trapping properties of DA white dwarf models with various thicknesses of the hydrogen envelope. Our predictions are compared with the standard assumption of diffusive equilibrium in the trace-element approximation. We find that element diffusion markedly weakens the presence of mode trapping originating in the outer layers of the models, even for the case of thin hydrogen envelopes. ER - TY - Journal T1 - Time-dependent diffusion in pulsating white dwarf stars: asteroseismology of G117-B15A A1 - Benvenuto, O. G. A1 - Córsico, A. H. A1 - Althaus, L. G. A1 - Serenelli, A. M. JO - Monthly Notices of the Royal Astronomical Society VL - 332 Y1 - 2002/5/1 SP - 399 EP - 408 KW - stars: evolution/ stars: individual: G117-B15A / stars: interiors/ stars: oscillations/ white dwarfs UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.332..399B&db_key=AST&high=42a068d47519812 N2 - We study the structural characteristic of the variable DA white dwarf G117-B15A by applying the methods of asteroseismology. For such a purpose, we construct white dwarf evolutionary models considering a detailed and up-to-date physical description as well as several processes responsible for the occurrence of element diffusion. We have considered several thicknesses for the outermost hydrogen layer, whereas for the inner helium-, carbon- and oxygen-rich layers we considered realistic profiles predicted by calculations of the white dwarf progenitor evolution. The stellar masses we have analysed cover the mass range of 0.50<=M */M_solar <=0.60. The evolution of each of the considered model sequences was followed down to very low effective temperatures; in particular, from 12500K on we computed the dipolar, linear, adiabatic oscillations with radial order k =1,...,4. We find that asteroseismological results are not univocal regarding mode identification for the case of G117-B15A . However, our asteroseismological results are compatible with spectroscopic data only if the observed periods of 215.2, 271.0 and 304.4s are due to dipolar modes with k =2,3,4, respectively. Our calculations indicate that the best fit to the observed period pattern of G117-B15A corresponds to a DA white dwarf structure with a stellar mass of 0.525M_solar , with a hydrogen mass fraction log(M _H /M *)>~-3.83 at an effective temperature T _eff ~11800K. The value of the stellar mass is consistent with that obtained spectroscopically by Koester & Allard. ER - TY - Journal T1 - Calculation of the masses of the binary star HD 93205 by application of the theory of apsidal motion A1 - Benvenuto, O. G. A1 - Serenelli, A. M. A1 - Althaus, L. G. A1 - Barbá, R. H. A1 - Morrell, N. I. JO - Monthly Notices of the Royal Astronomical Society VL - 330 Y1 - 2002/2/1 SP - 435 EP - 442 KW - BINARIES: ECLIPSING/ STARS: EARLY-TYPE/ STARS: EVOLUTION/ STARS: FUNDAMENTAL PARAMETERS/ STARS: INDIVIDUAL: HD 93205/ STARS: INTERIORS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.330..435B&db_key=AST&high=42a068d47519812 N2 - We present a method to calculate masses for components of both eclipsing and non-eclipsing binary systems as long as their apsidal motion rates are available. The method is based on the fact that the equation that gives the rate of apsidal motion is a supplementary equation that allows the computation of the masses of the components, if their radii and the internal structure constants can be obtained from theoretical models. For this reason the use of this equation makes the method presented here model dependent . We apply this method to calculate the mass of the components of the non-eclipsing massive binary system HD 93205 , which is suspected to be a very young system. To this end, we have computed a grid of evolutionary models covering the mass range of interest, and taking the mass of the primary (M ₁ ) as the only independent variable, we solve the equation of apsidal motion for M ₁ as a function of the age of the system. The mass of the primary that we find ranges from for zero-age main-sequence models, which sets an upper limit for M ₁ , down to for an age of 2Myr. Accordingly, the upper limit derived for the mass of the secondary is in very good agreement with the masses derived for other O8V stars occurring in eclipsing binaries. ER - TY - Journal T1 - Evolution of white dwarfs as a probe of theories of gravitation: the case of Brans-Dicke A1 - Benvenuto, O. G. A1 - Althaus, L. G. A1 - Torres, Diego F. JO - Monthly Notices of the Royal Astronomical Society VL - 305 Y1 - 1999/5/1 SP - 905 EP - 919 KW - GRAVITATION/ METHODS: ANALYTICAL/ STARS: LUMINOSITY FUNCTION/ MASS FUNCTION/ WHITE DWARFS/ COSMOLOGY: THEORY UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.305..905B&db_key=AST&high=42a068d47519812 N2 - Theories with varying gravitational constant G have long been studied. Among them, the most promising candidates as alternatives to standard general relativity are known as scalar-tensor theories. They are consistent descriptions of the observed Universe as well as the low-energy limit of several pictures of unified interactions. Thus, increasing interest in the astrophysical, gravitational wave and pulsar evolution consequences of such theories has been sparked over the last few years. In this work we study the evolution of white dwarf stars in the framework of the simplest model of scalar-tensor theory: Brans-Dicke gravity. We assume that the star is able to see the cosmological evolution of G (obtained from relativistic equations) while adopting a Newtonian model for describing its structure. This allows us to determine how the G variation affects the energetics of the stellar interior. The white dwarfs are analysed employing a well-tested computer code, with state-of-the-art data for the equation of state, opacities, neutrinos, etc.; all these characteristics are carefully described in the text. We compute the theoretical white dwarf luminosity function and use previous observational data to compare with and extract conclusions on the feasibility of the gravitational theory analysed. We find several striking results. The cooling of white dwarfs is strongly accelerated, particularly for massive stars and low luminosities, even if the Omicr parameter of Brans-Dicke theory is big enough to accord well with any other test of gravitation. This uncommon cooling process translates into several distinctive features of white dwarf evolution, among which are (a) a new profile of luminosity versus fractional mass and age, (b) different central temperature versus surface luminosity, (c) low masses of progenitors, and most importantly (d) an appreciable variation in the luminosity function. We finally analyse the possibilities of, when precise data with unique interpretation are available, converting this into a powerful new test of gravitation. ER - TY - Journal T1 - The phase transition from nuclear matter to quark matter during proto-neutron star evolution A1 - Benvenuto, O. G. A1 - Lugones, G. JO - Monthly Notices of the Royal Astronomical Society VL - 304 Y1 - 1999/4/1 SP - L25 EP - L29 KW - EQUATION OF STATE/ STARS: NEUTRON/ SUPERNOVAE: GENERAL/ SUPERNOVAE: INDIVIDUAL: SN 1987A UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.304L..25B&db_key=AST&high=42a068d47519812 N2 - We explore the occurrence of a phase transition from nuclear matter to quark matter in proto-neutron stars. To this end, we employ recent results on such a phase transition in the presence of an electron-neutrino-degenerate gas, based on a mean field model nuclear equation of state together with a quark matter equation of state as described by the MIT `bag model'. Those results show that this neutrino gas does not favour the transition. By comparison with the proto-neutron star evolutionary calculations of Keil & Janka, we find that, if the bag constant B has a value B <= 126 MeV fm^-3, the deconfinement transition indeed occurs. We also find that, if B >= 100 MeV fm^-3, the phase transition is delayed by the presence of neutrinos by a few seconds after core bounce, thus providing a natural explanation for the second peak of neutrino emission detected in SN 1987A by the Kamiokande Group. The transition to quark matter and its subsequent decay should affect proto-neutron star evolution and supernova explosions in a non-trivial way. ER - TY - Journal T1 - Grids of white dwarf evolutionary models with masses from M=0.1 to 1.2 m_solar A1 - Benvenuto, O. G. A1 - Althaus, L. G. JO - Monthly Notices of the Royal Astronomical Society VL - 303 Y1 - 1999/2/1 SP - 30 EP - 38 KW - STARS: EVOLUTION/ STARS: INTERIORS/ LUMINOSITY FUNCTION/ MASS FUNCTION/ PULSARS: GENERAL/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.303...30B&db_key=AST&high=42a068d47519812 N2 - We present detailed evolutionary calculations for carbon-oxygen- and helium-core white dwarf models with masses ranging from M= 0.1 to 1.2 M_solar and for metallicities Z = 0.001 and 0. The sequences cover a wide range of hydrogen envelopes as well. We have taken finite-temperature effects fully into account by means of a detailed white dwarf evolutionary code, in which updated radiative opacities and equations of state for hydrogen and helium plasmas are considered. The energy transport by convection is treated within the formalism of the full-spectrum turbulence theory, as given by the self-consistent model of Canuto, Goldman & Mazzitelli. Convective mixing, crystallization, hydrogen burning and neutrino energy losses are taken into account as well. The set of models presented here is very detailed and should be valuable, particularly for the interpretation of observational data on low-mass white dwarfs recently discovered in numerous binary configurations, and also for the general problem of determining the theoretical luminosity function for white dwarfs. In this context, we compare our cooling sequences with the observed white dwarf luminosity function recently improved by Leggett, Ruiz & Bergeron and we obtain an age for the Galactic disc of ~ 8 Gyr. Finally, we apply the results of this paper to derive stellar masses of a sample of low-mass white dwarfs. ER - TY - Journal T1 - Evolution of helium white dwarfs with hydrogen envelopes A1 - Benvenuto, O. G. A1 - Althaus, L. G. JO - Monthly Notices of the Royal Astronomical Society VL - 293 Y1 - 1998/1/1 SP - 177 KW - HELIUM/ STELLAR EVOLUTION/ WHITE DWARF STARS/ HYDROGEN/ STELLAR ENVELOPES/ STELLAR CORES/ PULSARS/ EQUATIONS OF STATE/ HERTZSPRUNG-RUSSELL DIAGRAM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998MNRAS.293..177B&db_key=AST&high=42a068d47519812 N2 - The present study is aimed at exploring the effects of hydrogen envelopes on the structure and evolution of low- and intermediate-mass, helium white dwarfs. To this end, we compute the evolution of models of helium white dwarfs with masses ranging from 0.15 to 0.5 solar masses for low and intermediate effective temperatures. The calculations are carried out by means of a detailed white dwarf evolutionary code in which updated radiative opacities and equations of state for hydrogen and helium plasmas are considered. We also take into account both convective mixing in the outer layers occurring at low luminosities and the presence of hydrogen burning at the bottom of the hydrogen-rich envelope by means of the inclusion of a detailed network of thermonuclear reaction rates. Our attention is focused mainly on that phase of evolution where finite-temperature effects are particularly significant. We find that thick hydrogen envelopes appreciably modify the radii and surface gravity of the nonhydrogen models, especially in the case of low-mass configurations. The computations presented here represent the most detailed models of helium white dwarfs with hydrogen envelopes presently available. ER - TY - Journal T1 - DB white dwarf evolution in the frame of the full spectrum turbulence theory A1 - Benvenuto, O. G. A1 - Althaus, L. G. JO - Monthly Notices of the Royal Astronomical Society VL - 288 Y1 - 1997/7/1 SP - 1004 EP - 1014 KW - CONVECTION/ STARS: EVOLUTION/ STARS: VARIABLES: OTHER/ WHITE DWARFS. UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997MNRAS.288.1004B&db_key=AST&high=42a068d47519812 N2 - We present an analysis of the evolution of carbon-oxygen DB white dwarfs (helium-rich envelope) for a wide range of effective temperatures and luminosities. To this end, we employ a full stellar evolution code, in which we include a new equation of state for helium plasmas recently developed by Saumon, Chabrier & Van Horn and new OPAL radiative opacities. The most important feature of our models is that the transport of energy by convection is described by the full spectrum turbulence theory. In particular, we have adopted two versions of this theory for stellar convection: the Canuto & Mazzitelli theory and the more recent, self-consistent theory developed by Canuto, Goldman & Mazzitelli. Both theories, which have no free parameters and account for the whole spectrum of turbulent eddies, represent a great improvement compared to the mixing-length theory approach used thus far in almost all white dwarf studies. Neutrino energy losses as well as crystallization were taken into account. In order to explore the sensitivity of our results to various input model parameters, we vary the model mass from 0.5 to 1.0Msolar in intervals of 0.1Msolar, and the helium layer mass in the interval of 10^-6â‰®M_He/ M_*â‰®10^-2. The emphasis is put mainly on the behaviour of the evolving outer convection zone. In particular, we analyse the dependence of the location of the theoretical blue edge of the instability strip on the various input parameters. We find that the new ingredients we have incorporated in this study - mostly the new formulations for stellar convection - lead to theoretical blue edges in agreement with observations of pulsating DB white dwarfs. In this context, the Canuto, Goldman & Mazzitelli self-consistent theory yields theoretical blue edges somewhat hotter than those given by the Canuto & Mazzitelli theory, which is more consistent with a recent determination of the effective temperature of the hot DBV GD358. Contrary to previous results, we find that, according to the new theories for convection, non-variable DB white dwarfs falling within the instability strip cannot be low-mass configurations. In order to compare with previous computations, we include in our calculations the most common parametrizations of the mixing-length theory usually employed in almost all previous white dwarf studies. In this context, we find that the ML2 parametrization provides a reasonable agreement with the observed blue edge for the DB instability strip. However, the profile of the outer convective zone given by the mixing-length theory is markedly different from that given by both of the new convective formulations. ER - TY - Journal T1 - The Structure and Thermal Evolution of Strange Dwarf Stars A1 - Benvenuto, O. G. A1 - Althaus, L. G. JO - Astrophysical Journal VL - 462 Y1 - 1996/5/1 SP - 364 KW - DENSE MATTER/ ELEMENTARY PARTICLES/ STARS: INTERIORS/ STARS: WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...462..364B&db_key=AST&high=42a068d47519812 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...462..364B&db_key=AST ER - TY - Journal T1 - Luminosity evolution of strange dwarf stars A1 - Benvenuto, O. G. A1 - Althaus, L. G. JO - Physical Review D VL - 53 Y1 - 1996/1/1 SP - 635 EP - 638 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996PhRvD..53..635B&db_key=AST&high=42a068d47519812 N2 - We study the evolution of strange dwarf stars of 0.4, 0.55, and 0.8 M_solar in the range of luminosities attributed to white dwarf stars. It is shown that, if the density at the base of the normal matter envelope is slightly lower than the density at which the onset of neutron drip occurs, these objects will have an evolution observationally indistinguishable from that corresponding to normal white dwarfs. This result is independent of the chemical composition of the high density, normal matter layers. However, strange dwarfs should behave very differently from white dwarfs in mass exchanging close binary systems. ER - TY - Journal T1 - White Dwarf Evolution and Crystallization A1 - Benvenuto, O. G. A1 - Althaus, L. G. JO - Astrophysics and Space Science VL - 234 Y1 - 1995/12/1 SP - 11 EP - 25 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Ap%26SS.234...11B&db_key=AST&high=42a068d47519812 N2 - Not Available ER - TY - Journal T1 - Strange matter equation of state in the quark mass-density-dependent model A1 - Benvenuto, O. G. A1 - Lugones, G. JO - Physical Review D VL - 51 Y1 - 1995/2/1 SP - 1989 EP - 1993 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995PhRvD..51.1989B&db_key=AST&high=42a068d47519812 N2 - We study the properties and stability of strange matter at T=0 in the quark mass-density-dependent model for noninteracting quarks. We found a wide ``stability window'' for the values of the parameters (C,M_s0) and the resulting equation of state at low densities is stiffer than that of the MIT bag model. At high densities it tends to the ultrarelativistic behavior expected because of the asymptotic freedom of quarks. The density of zero pressure is near the one predicted by the bag model and not shifted away as stated before; nevertheless, at these densities the velocity of sound is ~=50% larger in this model than in the bag model. We have integrated the equations of stellar structure for strange stars with the present equation of state. We found that the mass-radius relation is very much the same as in the bag model, although it extends to more massive objects, due to the stiffening of the equation of state at low densities. ER - TY - Journal T1 - MGS MAG/ER observations at the magnetic pileup boundary of Mars: draping enhancement and low frequency waves A1 - Bertucci, C. A1 - Mazelle, C. A1 - Crider, D. H. A1 - Mitchell, D. L. A1 - Sauer, K. A1 - Acuña, M. H. A1 - Connerney, J. E. P. A1 - Lin, R. P. A1 - Ness, N. F. A1 - Winterhalter, D. JO - Advances in Space Research VL - 33 Y1 - 2004/1/1 SP - 1938 EP - 1944 KW - Solar wind interaction with unmagnetized bodies/ Mars/ MPB/ Draping/ Low frequency waves UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..33.1938B&db_key=AST&high=42a068d47521132 N2 - The magnetic pileup boundary (MPB) is a sharp, thin, and permanent plasma boundary reported, up to now, at comets and Mars, and located between the bow shock and the ionospheric boundary. The MPB separates the magnetosheath, a region with high wave activity, from the magnetic pileup region, where the interplanetary magnetic field piles up regularly in front of the planetary obstacle. We use magnetic field and electron plasma measurements from the MAG/ER experiment onboard the Mars Global Surveyor spacecraft to study two characteristic features of the MPB. The first feature is the sudden enhancement of the magnetic field line draping at the MPB. This new signature reveals that the MPB marks the entry into the veritable induced magnetosphere, where the magnetic field topology is more regular, in opposition to what is observed in the magnetosheath. Secondly, we study the properties and the occurrence of compressive, linearly polarized, low frequency waves, frequently observed on both sides of the boundary. An analysis of the correlation between the magnetic and the electron data reveals that on the upstream side the waves are mirror mode waves, while on the downstream side they are large amplitude, quasi-monochromatic fast magnetosonic waves. The presence of these features at other atmospheric, unmagnetized bodies can be used as indicators of the existence of a MPB. ER - TY - Journal T1 - Magnetic field draping enhancement at Venus: Evidence for a magnetic pileup boundary A1 - Bertucci, C. A1 - Mazelle, C. A1 - Slavin, J. A. A1 - Russell, C. T. A1 - Acuña, M. H. JO - Geophysical Research Letters VL - 30 Y1 - 2003/9/1 EP - 1 KW - Magnetospheric Physics: Solar wind interactions with unmagnetized bodies/ Magnetospheric Physics: Planetary magnetospheres (5443/ 5737/ 6030)/ Planetology: Solar System Objects: Venus UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GeoRL..30qSSC1B&db_key=AST&high=42a068d47521132 N2 - The absence of a global-scale dynamo-generated magnetic field and the existence of an ionosphere at Venus and Mars caused many to predict that their solar wind interaction would be similar. After Pioneer Venus Orbiter (PVO) observations, it was concluded that the global aspects of the Venusian interaction could be well described by single-fluid models. According to these models, the magnetic field draping should develop progressively from the shock down to the ionopause. A recent study at Mars, where a ``Venus-like'' interaction was expected, showed that draping is prominent only inside the magnetic pileup boundary (MPB), a well-defined plasma boundary located between the shock and the ionopause first reported at comets, but never at Venus. From an identical analysis on PVO magnetometer data, we report a dramatic enhancement of draping on the dayside of Venus. Then, we deduce the existence of a Venusian counterpart of the Martian and cometary MPB. ER - TY - Journal T1 - Magnetic field draping enhancement at the Martian magnetic pileup boundary from Mars global surveyor observations A1 - Bertucci, C. A1 - Mazelle, C. A1 - Crider, D. H. A1 - Vignes, D. A1 - Acuña, M. H. A1 - Mitchell, D. L. A1 - Lin, R. P. A1 - Connerney, J. E. P. A1 - Rème, H. A1 - Cloutier, P. A. A1 - Ness, N. F. A1 - Winterhalter, D. JO - Geophysical Research Letters VL - 30 Y1 - 2003/1/1 SP - 71 EP - 1 KW - Planetology: Solar System Objects: Mars/ Magnetospheric Physics: Planetary magnetospheres (5443/ 5737/ 6030)/ Magnetospheric Physics: Solar wind interactions with unmagnetized bodies/ UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GeoRL..30b..71B&db_key=AST&high=42a068d47521132 N2 - The Magnetic Pileup Boundary (MPB) is a sharp and permanent plasma boundary located between the bow shock and the ionospheric boundary, reported so far at Mars and comets. We use Mars Global Surveyor Magnetometer data to do a quantitative analysis of the magnetic field geometry in the surroundings of the Martian MPB. As a result, we report for the first time a dramatic enhancement of the magnetic field draping at this boundary. This new feature, already reported at comets, is independent of the presence of the crustal magnetic sources. Comparisons with similar results across the Martian and cometary magnetotails reveal that the MPB and the magnetotail boundary are connected. Moreover, the study of this feature can help understand the physics of the Venusian magnetic barrier. ER - TY - Journal T1 - Multicolor photometry of ten Seyfert 1 galaxies. A1 - Boris, N. V. A1 - Donzelli, C. J. A1 - Pastoriza, M. G. A1 - Rodriguez-Ardila, A. A1 - Ferreiro, D. L. JO - Astronomy and Astrophysics VL - 384 Y1 - 2002/3/1 SP - 780 EP - 792 KW - Galaxies: photometry/ Galaxies: Active/ Galaxies: Seyfert UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...384..780B&db_key=AST&high=42a068d47524259 N2 - We present new valuable BVI photometry of ten Seyfert 1 galaxies and narrow band Halpha images for six of these objects. The results indicate that the distribution of the luminosity of the sample has an amplitude of almost 4 mag with an average of M_B=-20.7. The observed morphologies are confined to early type galaxies. A barred structure is found in only 2 objects. Despite that early morphological types are dominant in this sample, integrated (B-V) colors are very blue. For instance, the SO galaxies show, on average, a (B-V)=0.78. This effect seems to be caused by the luminosity contribution of the active nucleus and/or the disk to the total luminosity of the galaxy. In the B band, the contribution of the active galactic nucleus to the total luminosity of the galaxy varies from 3% to almost 60% and the bulge to disk luminosity ratio (L_bulge/L_disk) ranges from 0.6 to 22. Signs of tidal interactions seem to be a common characteristic since they are observed in 6 of the objects and one of them seems to be located in a poor cluster not yet identified in the literature. In contrast, Halpha extended emission is rare, with only 1 galaxy showing clear evidence of it. Luminosity profile decomposition shows that the model Gauss + bulge + disk properly reproduces the surface brightness of the galaxies. However, in order to account for the luminosity profile, most of the disk galaxies need the inner truncated exponential form with a central cutoff radius ranging from 3 to 10 kpc. This is interpreted in terms of reddened regions that are well identified in the B-V color maps. These regions present very similar colors among them, with (B-V)~1.2. This fact could be associated with the presence of dust confined in the inner regions of the galaxies. ER - TY - Journal T1 - Ruprecht 55: an OB association at the edge of our Galaxy A1 - Bosch, Guillermo A1 - Barbá, Rodolfo A1 - Morrell, Nidia A1 - Niemela, Virpi A1 - Ostrov, Pablo A1 - Arnal, Marcelo A1 - Cappa, Cristina A1 - Morras, Ricardo A1 - de Castro, Guillermo Giménez JO - Monthly Notices of the Royal Astronomical Society VL - 341 Y1 - 2003/5/1 SP - 169 EP - 178 KW - stars: early-type/ ISM: bubbles/ ISM: kinematics and dynamics/ open clusters and associations: individual: Ruprecht 55/ Galaxy: structure UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.341..169B&db_key=AST&high=42a068d47526397 N2 - We present new spectroscopy in the optical range and 21-cm HI data covering the Ruprecht 55 (Ru 55) field in the Puppis window where several authors have proposed the existence of one (or two) clusters. We have determined new MK spectral types for about 50 stars in the region, finding 43 OB-type stars among them. LS 985 was found to be an O9 V + O9.5 III binary and it is the earliest type of star in our observed sample. We have identified a stellar OB association (Ru 55), which is most likely related to a depletion detected in our HI data, as: (i) they are located at the same distance (6 kpc), within observational errors; (ii) both have similar radial velocities (~67 km s^-1) (iii) current OB stars could have provided the energy needed to blow the cavity; (iv) the dynamical time-scale for the hole buildup matches the age estimated for the earliest OB stars; and (v) LS 985 might be responsible for ionizing the HI cavity inner walls close to it. ER - TY - Journal T1 - Narrow-band CCD photometry of giant H II regions A1 - Bosch, Guillermo A1 - Terlevich, Elena A1 - Terlevich, Roberto JO - Monthly Notices of the Royal Astronomical Society VL - 329 Y1 - 2002/1/1 SP - 481 EP - 496 KW - HII REGIONS/ GALAXIES: INDIVIDUAL: NGC 6822/ GALAXIES: INDIVIDUAL: M33/ GALAXIES: INDIVIDUAL: M101 HII/ GALAXIES: STAR CLUSTERS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.329..481B&db_key=AST&high=42a068d47526397 N2 - We have obtained accurate CCD narrow-band Hbeta and Halpha photometry of giant HII regions (GEHRs) in M33, NGC 6822 and M101. Comparison with previous determinations of emission-line fluxes shows large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion (sigma) derived from emission linewidths, we review the L(Hbeta)-sigma relation. A re-analysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we find that a subsample - which we refer to as young and single GEHRs - do follow a tight relation in the L-sigma plane. ER - TY - Journal T1 - The ionising cluster of 30 Doradus. IV. Stellar kinematics A1 - Bosch, G. A1 - Selman, F. A1 - Melnick, J. A1 - Terlevich, R. JO - Astronomy and Astrophysics VL - 380 Y1 - 2001/12/1 SP - 137 EP - 141 KW - STARS: EARLY-TYPE/ STARS: KINEMATICS/ BINARIES: SPECTROSCOPIC/ GALAXIES: CLUSTERS: GENERAL/ GALAXIES: MAGELLANIC CLOUDS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...380..137B&db_key=AST&high=42a068d47526397 N2 - On the basis of multislit spectroscopy of 180 stars in the ionising cluster of 30 Doradus we present reliable radial velocities for 55 stars. We calculate a radial velocity dispersion of ~35 km s^-1 for the cluster and we analyse the possible influence of spectroscopic binaries in this rather large velocity dispersion. We use numerical simulations to show that the observations are consistent with the hypothesis that all the stars in the cluster are binaries, and the total mass of the cluster is ~ 5 x 10⁵ M_sun. A simple test shows only marginal evidence for dynamical mass segregation which if present is most likely not due to dynamical relaxation. Based on observations collected at the European Southern Observatory. ER - TY - Journal T1 - The ionising cluster of 30 Doradus. II. Spectral classification for 175 stars A1 - Bosch, G. A1 - Terlevich, R. A1 - Melnick, J. A1 - Selman, F. JO - Astronomy and Astrophysics Supplement Series VL - 137 Y1 - 1999/5/1 SP - 21 EP - 41 KW - STARS: HERTZSPRUNG RUSSELL (HR) DIAGRAM/ STARS: LUMINOSITY FUNCTION/ MASS FUNCTION/ STARS: EARLY-TYPE/ ISM: DUST/ EXTINCTION/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ GALAXIES: MAGELLANIC CLOUDS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26AS..137...21B&db_key=AST&high=42a068d47526397 N2 - We present spectral types for 175 stars in the ionising cluster of 30 Doradus derived from multislit observations of 231 stars. Comparison with published classifications for 70 stars in common with other authors reveals excellent agreement with the exception of a few cases which are discussed in detail. Our new observations raise to 261 the total number of stars in 30 Dor with known spectral types, outside R136. We analyse the spatial distribution of these stars according to their spectral types, and find evidence for mass segregation. Based on observations collected at the European Southern Observatory. ER - TY - Journal T1 - Stellar Spectroscopy in NGC 6611: Binary Frequency and New Spectral Types of Several Early Type Stars A1 - Bosch, G. L. A1 - Morrell, N. I. A1 - Niemelä, V. S. JO - Revista Mexicana de Astronomia y Astrofisica VL - 35 Y1 - 1999/4/1 SP - 85 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999RMxAA..35...85B&db_key=AST&high=42a068d47526397 N2 - Not Available ER - TY - Journal T1 - Linear polarization of a group of symbiotic systems A1 - Brandi, E. A1 - García, L. G. A1 - Piirola, V. A1 - Scaltriti, F. A1 - Quiroga, C. JO - Astronomy and Astrophysics Supplement Series VL - 145 Y1 - 2000/8/1 SP - 197 EP - 214 KW - STARS: BINARIES: SYMBIOTIC/ STARS: BINARIES ECLIPSING/ STARS: VARIABLE STARS/ POLARIZATION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26AS..145..197B&db_key=AST&high=42a068d47500975 N2 - We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin. Based on observations taken at Complejo Astronómico El Leoncito (CASLEO), operated under an agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, the Secretaría de Ciencia y Tecnología de la Nación and the National Universities of La Plata, Córdoba and San Juan. ER - TY - Journal T1 - A spectrographic study of the symbiotic system HEN 1761 A1 - Brandi, E. A1 - Barba, R. A1 - Garcia, L. G. A1 - Beltran, N. JO - Astronomy and Astrophysics Supplement Series VL - 132 Y1 - 1998/10/1 SP - 281 EP - 289 KW - STARS: EMISSION-LINES/ SYMBIOTIC STARS/ STARS: VARIABLE STARS/ STARS: INDIVIDUAL: HEN 1761 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..132..281B&db_key=AST&high=42a068d47500975 N2 - This work presents the results of a spectroscopic study in the optical and near infrared region of the symbiotic star Hen 1761. Relative fluxes and radial velocities of emission and absorption lines are obtained on the basis of low, intermediate and high resolution spectra. Our observations show that this scarcely studied object underwent very important spectroscopic variations in the interval 1990-1995. The observed variations are quite similar to those of symbiotic stars where accretion events on a hot dwarf are responsible for an eruptive behavior. Some of the physical parameters of the system are derived. Based on observations taken at Complejo Astronómico El Leoncito (CASLEO), operated under an agreement between the Consejo Nacional de Investigaciones Cient\'{\i ER - TY - Journal T1 - A method for deriving stellar space densities A1 - Branham, R. L., Jr. JO - Astronomy and Astrophysics VL - 401 Y1 - 2003/4/1 SP - 951 EP - 958 KW - galactic structure/ methods/ data reduction UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...401..951B&db_key=AST&high=42a068d47503534 N2 - The fundamental integral equation of stellar statistics represents a direct, model-independent approach to calculating stellar densities. Many techniques exist for its solution, but some of these require assumptions, such as a Gaussian luminosity function or a specific form for the density function, that may be unrealistic. To solve the equation as an undeterdetermined total least squares system with Tikhanov regularization recognizes that the problem is ill-posed and generally ill-conditioned as well and offers decided advantages: it is unnecessary to assume a Gaussian luminosity function nor a specific form for the density function; discretization error in the kernel of the integral equation as well as the Poisson error in the star counts are accounted for; mean errors for the densities are calculated; the densities are constrained to be both continuous and positive. The greatest drawback to the method comes from the selection of the ridge parameter, but the drawback becomes surmountable. The method is first applied to three examples, general star counts, the distribution of K0 giants, and the distribution of M 2-M 4 dwarfs, and compared with densities calculated from methods such as Malmquist's and the (m, log pi ) table. Regularized total least squares competes well with these methods. Then the method is applied to a new data set from the AC2000.2 catalog to calculate the densities of M giants and supergiants in the directions of the north and south galactic poles. The densities decrease exponentially to near zero at 2000 pc, with half-density points near 550 pc. No evidence for asymmetry between the two hemispheres can be seen. ER - TY - Journal T1 - Orbit of Comet C/1850 Q1 (Bond) A1 - Branham, Richard L., Jr. JO - Publications of the Astronomical Society of Australia VL - 20 Y1 - 2003/1/1 SP - 184 EP - 188 KW - celestial mechanics/ comets: individual (C/1850 Q1)/ methods: data analysis UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003PASA...20..184B&db_key=AST&high=42a068d47503534 N2 - Comet C/1850 Q1 (Bond) is one of a number of comets catalogued with parabolic orbits. Given that there are sufficient observations, 104in right ascension and 103in declination, it proves possible to calculate a better orbit. Some of the difficulties of working with 19th century observations, which show considerable scatter, are discussed. Rectangular coordinates, both of the comet and the Sun, are interpolated by a recursive version of Aitken's method, rendering unnecessary the need to specify an order for the interpolation. Comet Bond's orbit is slightly hyperbolic. ER - TY - Journal T1 - The Sun's Distance from the Galactic Plane A1 - Branham, R. L., Jr. JO - Astrophysics and Space Science VL - 287 Y1 - 2003/1/1 SP - 313 EP - 325 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Ap%26SS.287..313B&db_key=AST&high=42a068d47503534 N2 - Use is made of 93,106 parallaxes from the Hipparcos catalog, with a mixture of spectrum-luminosity classes, to derive the position of the Galactic plane. The reduction technique, mixed total least squares-least squares, takes into account the errors in the parallaxes, and the condition that the direction cosines of the Galactic pole have unit Euclidean norm is rigorously enforced. To obtain an acceptable solution it is necessary to eliminate the stars of classes O and B that belong to the Gould belt. The Sun is found to lie 34.56+/-0.56 pc above the plane. The coordinates of the Galactic pole, l_g, b_g, are found to be: l_g=0.°004+/-0.°039 b_g=89.°427+/-0.°035. This agrees well with what radio observations find and demonstrates that the IAU's recommendation in 1960 to use only radio observations to determine the Galactic pole, although correct at the time because of the paucity of optical observations, can no longer be justified given the plethora of observations contained in the Hipparcos catalog and an adequate reduction technique, unavailable in 1960. The reduction technique is also demonstrably superior to others because it involves fewer assumptions and calculates smaller mean errors. ER - TY - Journal T1 - Kinematics of OB Stars A1 - Branham, Richard L., Jr. JO - Astrophysical Journal VL - 570 Y1 - 2002/5/1 SP - 190 EP - 197 KW - Galaxies: Kinematics and Dynamics/ Methods: Data Analysis UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...570..190B&db_key=AST&high=42a068d47503534 N2 - The kinematics of 1817 stars of class O-B5 are examined. The 1655 stars with distances up to 1 kpc are taken from the Hipparcos catalog and 162 stars with distances greater than 1 kpc from Westlin's study of OB stars. The Ogorodnikov-Milne model of Galactic kinematics, with Edmondson's second-order terms included, is used for the equations of condition and mixed total least squares-least squares (TLS-LS) is used for the reduction method. Reasonable values for the parameters of Galactic kinematics are obtained. In particular, Oort A and B constants yield a Galactic rotation of 258.7+/-34.29 km s^-1 if we take the distance of the Sun from the Galactic center as 8.5+/-1.1 kpc. Although lower than the higher values obtained by some other investigators and higher than the IAU's recommended 220+/-20 km s^-1, all the determinations fall with their stated mean errors. Thus, no evidence for a significant difference in the various determinations exists. Evidence does exist, however, to assert that the TLS-LS reduction model with second-order terms seems superior to ordinary least-squares with only first-order terms. ER - TY - Journal T1 - Astronomical data reduction with total least squares A1 - Branham, Richard L. JO - New Astronomy Review VL - 45 Y1 - 2001/12/1 SP - 649 EP - 661 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001NewAR..45..649B&db_key=AST&high=42a068d47503534 N2 - Although astronomers have been involved with the development and use of least squares, and alternatives, they have made insufficient use of total least squares: least squares that allow for error in the equations of condition as well as the observations. There exist, however, problems of astronomical data reduction for which total least squares represents the ideal mathematical tool. Among these problems are the differential correction of an orbit and the determination of parameters of Galactic kinematics. Total least squares, although more computationally demanding than ordinary least squares, can be used in any situation where the latter is applicable. However, care must be paid to the proper scaling of the data matrix. The method merits greater attention by the astronomical community. ER - TY - Journal T1 - The Parameters of Galactic Kinematics Determined from Total Least Squares A1 - Branham, R. L., Jr. JO - Revista Mexicana de Astronomia y Astrofisica VL - 36 Y1 - 2000/10/1 SP - 97 EP - 112 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000RMxAA..36...97B&db_key=AST&high=42a068d47503534 N2 - Problems of Galactic kinematics have usually been solved by the method of least squares, but this may lead to biased results because least squares assume that error resides only in the observations, not in the equations of condition. The latter, however, generally incorporate error, at least in some of the columns of the data matrix. Total least squares represents the ideal mathematical tool for just this sort of problem. In this paper, the method, or better stated a mixed total-ordinary least squares method, is applied to over 100,000 stars taken from the Hipparcos catalog to calculate twelve parameters of Galactic kinematics: the nine components of the deformation tensor, related to such quantities as the Oort A and B parameters, the K term, Galactic vorticity, and the Solar motion. Reasonable values for all of these is obtained, showing that high quality astrometric data and an adequate reduction method can produce good results for global solutions when in the past this proved difficult or impossible. ER - TY - Journal T1 - A Covariance Matrix for Total Least Squares with Heteroscedastic Data A1 - Branham, Richard L., Jr. JO - Astronomical Journal VL - 117 Y1 - 1999/4/1 SP - 1942 EP - 1948 KW - ASTROMETRY/ CELESTIAL MECHANICS/ STELLAR DYNAMICS/ METHODS: DATA ANALYSIS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....117.1942B&db_key=AST&high=42a068d47503534 N2 - Total least squares calculates a least-squares solution when error arises not only in the observations themselves, but also in the equations of condition. The covariance matrix constitutes a vital adjunct to any least-squares solution and should always be calculated. Although covariance matrices exist for total least squares, they assume that the observations, although incorporating normal, statistical scatter, nevertheless embody a single, underlying mean error, an assumption known in statistics as ``homoscedasticity.''Yet, many observations in astronomy violate this assumption, particularly when the observations are made over a long time span and with instruments of different precision. This paper gives a covariance matrix for heteroscedastic observations of this nature. When the observations become homoscedastic, this covariance matrix reduces to the standard covariance matrix for total least squares. When the equations of condition are error-free, the covariance matrix coincides with the standard covariance matrix for ordinary least squares. This covariance matrix is applied to 1140 photographic observations of Pluto that exhibit heteroscedastic scatter in order to estimate the mean errors, the covariances, and the correlations of the solution. ER - TY - Journal T1 - Are There Significant Equator and Equinox Errors in the FK5 System? A1 - Branham, R. L., Jr. A1 - Sanguín, J. G. JO - Revista Mexicana de Astronomia y Astrofisica VL - 34 Y1 - 1998/4/1 SP - 3 KW - ASTROMETRY/ CORRECTION/ EQUATORS/ EQUINOXES/ ERRORS/ ASTEROIDS/ DECLINATION/ INDEXES (DOCUMENTATION)/ SECULAR VARIATIONS/ SOLAR ORBITS/ SUBJECTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998RMxAA..34....3B&db_key=AST&high=42a068d47503534 N2 - 11739 observations in right ascension and 11656 in declination, made between 1847 and 1993, of 21 minor planets are used to estimate the equinox and equator errors of the FK5 fundamental system. Each minor planet's orbit was corrected along with corrections for the Earth's orbit and the FK5 equator, and equinox errors with their secular variations. No strong evidence exists for an equator correction or secular variation. Evidence does exist, however, for an equinox correction of the order of 0.18" at the approximate epoch 1970 and for a possible motion of the equinox of about 0.11" 0.14" per century. External evidence confirms at least part of these conclusions. ER - TY - Journal T1 - Total Least Squares: an Ideal Mathematical Tool for Galactic Kinematics A1 - Branham, Richard L., Jr. JO - Astrophysics and Space Science VL - 257 Y1 - 1997/1/1 SP - 107 EP - 121 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997Ap%26SS.257..107B&db_key=AST&high=42a068d47503534 N2 - Problems of Galactic kinematics have usually been solved by the method of least squares. As has been known for over forty years, this may lead to biased results because least squares assume that error resides only in the observations, not in the equations of condition. The latter, however, generally incorporate error, at least in some of the columns of the data matrix. Total least squares represents the ideal mathematical tool for just this sort of problem. In this paper the method, or better stated a mixed total-ordinary least squares method, is applied to 3100 stars taken from the Bright star Catalog to calculate eight parameters of Galactic kinematics: two corrections to the precessional constants, the Oort A and B parameters, the components of solar motion, and the K term. Total least squares calculates a reasonable solution, whereas ordinary least squares fails completely. ER - TY - Journal T1 - Sites for Fundamental Astromety - are High Latitudes best A1 - Branham, R. L., Jr. JO - Quarterly Journal of the Royal Astronomical Society VL - 36 Y1 - 1995/12/1 SP - 351 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995QJRAS..36..351B&db_key=AST&high=42a068d47503534 N2 - Not Available ER - TY - Journal T1 - Multivariate orthogonal regression in astronomy A1 - Branham, Richard L., Jr. JO - Celestial Mechanics and Dynamical Astronomy VL - 61 Y1 - 1995/3/1 SP - 239 EP - 251 KW - ASTRONOMY/ DATA REDUCTION/ LEAST SQUARES METHOD/ ORTHOGONAL FUNCTIONS/ REGRESSION ANALYSIS/ APPROXIMATION/ ERROR ANALYSIS/ KINEMATICS/ MATRICES (MATHEMATICS)/ TWO BODY PROBLEM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995CeMDA..61..239B&db_key=AST&high=42a068d47503534 N2 - Total least squares considers the problem of data reduction when error resides in both the data itself and also in the equations of condition. Error may be found in all of the columns of the matrix of the equations of condition, or merely in some; the latter situation is referred to as a mixed total least squares problem. A covariance matrix may be derived for total least squares. Both memory and operation count requirements are more severe than for ordinary least squares: about four times more memory and, if the problem involves n unknowns, 15n + 4 more arithmetic operations. The method, applicable in any situation where ordinary least squares is relevant, including the estimation of scaled variables, is applied to three examples, one artificial and two taken from astronomy: the estimation of various parameters of Galactic kinematics, and the differential correction of a planetary orbit. In these two examples the results from total least squares are superior to those from ordinary least squares. ER - TY - Journal T1 - A tree code for planetesimal dynamics: comparison with a hybrid direct code A1 - Brunini, Adrián A1 - Viturro, Héctor R. JO - Monthly Notices of the Royal Astronomical Society VL - 346 Y1 - 2003/12/1 SP - 924 EP - 932 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.346..924B&db_key=AST&high=42a068d47505393 N2 - We present a tree code for simulations of collisional systems dominated by a central mass. We describe the implementation of the code and the results of some test runs with which the performance of the code was tested. A comparison between the behaviour of the tree code and a direct hybrid integrator is also presented. The main result is that tree codes can be useful in numerical simulations of planetary accretion, especially during intermediate stages, where possible runaway accretion and dynamical friction lead to a population with a few large bodies in low-eccentricity and low-inclination orbits embedded in a large swarm of small planetesimals in rather excited orbits. Some strategies to improve the performance of the code are also discussed. ER - TY - Journal T1 - Cratering rate on the jovian system: the contribution from Hilda asteroids A1 - Brunini, Adrián A1 - di Sisto, Romina P. A1 - Orellana, Rosa B. JO - Icarus VL - 165 Y1 - 2003/10/1 SP - 371 EP - 378 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Icar..165..371B&db_key=AST&high=42a068d47505393 N2 - We study the dynamical evolution of the Hilda group of asteroids trough numerical methods, performing also a collisional pseudo-evolution of the present population, in order to calculate the rate of evaporation and its contribution to the cratering history of the Galilean satellites. If the present population of small asteroids in the Hilda's region follows the same size distribution observed at larger radii, we find that this family is the main contributor to the production of small craters (i.e., crater with diameters /d~4 km) on the Galilean system, overcoming the production by Jupiter Family Comets and by Trojan asteroids. The results of this investigation encourage further observational campaigns, in order to determine the size distribution function of small Hilda asteroids. ER - TY - Journal T1 - The Existence of a Planet beyond 50 AU and the Orbital Distribution of the Classical Edgeworth-Kuiper-Belt Objects A1 - Brunini, A. A1 - Melita, M. D. JO - Icarus VL - 160 Y1 - 2002/11/1 SP - 32 EP - 43 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Icar..160...32B&db_key=AST&high=42a068d47505393 N2 - We study the effects of a Mars-like planetoid with a semimajor axis at about ~60 AU orbiting embedded in the primordial Edgeworth-Kuiper belt (EKB). The origin of such an object can be explained in the framework of our current understanding of the origin of the outer Solar System, and a scenario for the orbital transport mechanism to its present location is given. The existence of such an object would produce a gap in the EKB distribution with an edge at about 50 AU, which seems to be in agreement with the most recent observations. No object at low eccentricity with semimajor axis beyond 50 AU has been detected so far, even though the present observing capabilities would allow an eventual detection (B. Gladman et al. 1998, Astron. J.116, 2042-2054 D. Jewitt et al. 1998, Astron. J.115, 2125-2135 E. I. Chiang and M. E. Brown 1999, Astron. J.118, 1411-1422 R. L. Allen et al. 2000, Astrophys. J.549, 241-244 C. A. Trujillo et al. 2001, Astron. J.122, 457-473 B. Gladman et al. 2001, Astron. J.122, 1051-1066 C. A. Trujillo and M. E. Brown 2001, Astrophys. J.554, 95-98). Finally, ranges for the magnitude and proper motion of the proposed object are given. ER - TY - Journal T1 - Dynamics of the Edgeworth-Kuiper Belt beyond 50 AU. Spread of a primordial thin disk A1 - Brunini, A. JO - Astronomy and Astrophysics VL - 394 Y1 - 2002/11/1 SP - 1129 EP - 1134 KW - Kuiper Belt/ comets: general/ solar system: general UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...394.1129B&db_key=AST&high=42a068d47505393 N2 - In this paper we report numerical simulations of the dynamical evolution of the region a >50 AU. We found that some dynamical effects such as high-order secular resonances with the rate of precession of Neptune's node of the form k dot Omega - dot Omega_Nep with k=4,5,... or combined mean motion resonances with Uranus and Neptune of the form k n_N + j n_U + m n ~ 0 may increase the area of a very thin primordial disk in this region by a factor of up to 2 after 4.5 Gy of evolution. ER - TY - Journal T1 - Constraints to Uranus' Great Collision III: The Origin of the Outer Satellites A1 - Brunini, Adrián A1 - Parisi, Mirta Gabriela A1 - Tancredi, Gonzalo JO - Icarus VL - 159 Y1 - 2002/9/1 SP - 166 EP - 177 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Icar..159..166B&db_key=AST&high=42a068d47505393 N2 - The theory of satellite loss resulting from a giant impact on Uranus (Parisi and Brunini 1997, Planet. Space Sci.45, 181-187) is revisited, in the light of the discovery of its five outer moons (Gladman et al. 1998, Nature392, 897-899 Gladman et al. 2000, Icarus147, 320-324 erratum 148, 320). Physical conditions and dynamical constraints in the great collision scenario and restrictions in the possible mechanisms for the origin of the outer uranian satellites are obtained from the knowledge of their actual orbital properties. We conclude that the existence of these moons implies that their origin must be connected to a breakup process. Other scenarios for their origin cast serious doubts on the occurrence of a giant collision at the end of Uranus' formation process to account for its large spin axis obliquity. ER - TY - Journal T1 - On the accretion of Uranus and Neptune A1 - Brunini, A. A1 - Melita, M. D. JO - Monthly Notices of the Royal Astronomical Society VL - 330 Y1 - 2002/2/1 SP - 184 EP - 186 KW - ACCRETION/ ACCRETION DISCS/ PLANETS AND SATELLITES: FORMATION/ PLANETS AND SATELLITES: INDIVIDUAL: URANUS/ PLANETS AND SATELLITES: INDIVIDUAL: NEPTUNE/ SOLAR SYSTEM: FORMATION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.330..184B&db_key=AST&high=42a068d47505393 N2 - In this paper , we discuss some problems concerning the formation of Uranus and Neptune. We find that the adoption of reduced Hill spheres as the region of close interaction between planetesimals introduces an enhancement of the gravitational cross-sections in previous numerical simulations. We also discuss a way to make possible the formation of Uranus and Neptune on time-scales shorter than the age of the Solar system. ER - TY - Journal T1 - Numerical simulations of the accretion of Uranus and Neptune A1 - Brunini, A. A1 - Fernández, J. A. JO - Planetary and Space Science VL - 47 Y1 - 1999/5/1 SP - 591 EP - 605 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999P%26SS...47..591B&db_key=AST&high=42a068d47505393 N2 - The accretion process of the outer planets was one of the most collective phenomena during the formation of the solar system. From the region of the terrestrial planets up to its outermost boundary, the Oort cloud, the solar system has been strongly influenced by this process ([Fernandez and Gallardo, 1996]). Much progress has been done in our understanding of the formation of the outer planets and scattering of the residual mass from the early theoretical research of [Safronov, 1972]. Nevertheless, there are several aspects not yet understood that deserve further study. ER - TY - Journal T1 - Stability of orbits within the Disc around the binary system BD+31°643 A1 - Brunini, A. JO - Planetary and Space Science VL - 47 Y1 - 1998/12/1 SP - 175 EP - 180 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998P%26SS...47..175B&db_key=AST&high=42a068d47505393 N2 - In this paper, we analyze the stability of motion of planetary bodies orbiting binary stars, with special emphasis on possible planetary bodies within the recently discovered disk around BD+31, 643°. In accordance with previous estimates, we found that beyond ~4 times the mean orbital separation of the components of the binary from the center of mass of the system, the presence of planetary embryos within circumbinary discs is possible. Our results also support that the central depletion observed in the structure of the disc around BD+31, 643° is due to tidal interaction with the binary. We have also investigated the dynamical stability of the disk against stellar encounters within a dense environment such as the young star cluster IC 348 where the binary system is immersed. We found that the inner portion of the disk remains almost unaffected by stellar perturbations. On the contrary, the outer region is strongly influenced by passing stars, suggesting that the observed disk is limited in extension by external perturbations. The available observational data indicates that the orbit of the binary is rather eccentric. This fact and the observed shift between the disc plane and the orbital plane of the binary, casts some doubts about the origin of the dust disk. ER - TY - Journal T1 - On the Existence of a Primordial Cometary Belt between Uranus and Neptune A1 - Brunini, A. A1 - Melita, M. D. JO - Icarus VL - 135 Y1 - 1998/10/1 SP - 408 EP - 414 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998Icar..135..408B&db_key=AST&high=42a068d47505393 N2 - The existence of stable orbits in the interplanetary region between Uranus and Neptune over the lifetime of the Solar System has been reported by Holman (1997, Nature 387, 785-788). A long-term integration of test particles in that zone resulted in a number of surviving bodies with semimajor axis roughly between 24 and 27 AU, and eccentricities and inclinations smaller than 10^-2 and 1 deg, respectively. According to up-to-date surveys, the total mass of this putative belt has been estimated as <= 10^-3 M_âŠ• and it would be composed of objects with radius smaller than 50 km. In this work we assess the plausibility of the existence of a real population of objects in such a belt. Time-reversal arguments rule out the possibility of capture in such long-term stable orbits, for example, of objects escaped from the Kuiper belt. So if a real population exists nowadays, it should have undergone the conditions of planetesimal accretion in the region. Hence, we have studied the orbital evolution of test particles under different kinds of plausible primordial scenarios. The conditions considered were mutual collisions and gravitational encounters, planetary migration and the presence of an adjacent Pluto-sized object. Under none of these conditions have we obtained a surviving substantial population on the reported belt region, from which it is concluded that, at present time, it would be very unlikely to find a subtantial number of primordial objects in those long-term stable orbits. ER - TY - Journal T1 - The cometary bombardment on the primitive asteroid belt A1 - Brunini, A. A1 - Huton, R. G. JO - Planetary and Space Science VL - 46 Y1 - 1998/8/1 SP - 997 EP - 1001 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998P%26SS...46..997B&db_key=AST&high=42a068d47505393 N2 - In this paper, we estimate the number of catastrophic collisions between asteroids and comets scattered from the Uranus-Neptune zone during the process of planetary accretion. We found that the change in slope at ~75 km in the size distribution for non-family asteroids could be produced by an intense bombardment of scattered comets in a short period of time after the accretion of Uranus and Neptune, provided that any asteroid with radius <=130-150 km received a catastrophic collision by scattered comets. Larger asteroids have probably not received any catastrophic collision, due to the small number of large comets. We also estimate that the total amount of mass in the primitive asteroid belt, before the depletion produced by dynamical and collisional processes, was not less than ~1800 times the present one. ER - TY - Journal T1 - Dynamical behaviour of the primitive asteroid belt A1 - Brunini, Adrian JO - Monthly Notices of the Royal Astronomical Society VL - 293 Y1 - 1998/2/1 SP - 405 KW - ASTEROID BELTS/ GRAVITATIONAL EFFECTS/ PLANETARY GRAVITATION/ GAS GIANT PLANETS/ JUPITER (PLANET)/ SATURN (PLANET) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998MNRAS.293..405B&db_key=AST&high=42a068d47505393 N2 - We consider the dynamical evolution and orbital stability of objects in the asteroid belt. A simple physical model, including full gravitational perturbations from both giant planets, is used to compute the dynamical evolution of 1000 test particles simulating the primitive asteroids. The criterion of planet crossing (or close approach in the case of resonant objects) is used to reject particles from the simulation. A total of 44 percent of the particles survived for the whole time-span covered by the numerical integration (about 10 exp 9 yr). The 4:1, 3:1, and, to a lesser extent, the 2:1 Kirkwood gaps are formed in about 10 exp 7 yr of evolution, representing direct numerical evidence about their gravitational origin. We found that the rms eccentricity and inclination of the sample experience a fast increase during the first 10 exp 6 yr. The final rms eccentricity is 0.11, about 60 percent smaller than the present rms eccentricity (0.17). Nevertheless, the gravitational action of the giant planets suffices to prevent the formation of large objects, allowing catastrophic collisions and the subsequent depletion of material from this zone of the solar system. ER - TY - Journal T1 - Stability of planets orbiting BD + 31deg643 A1 - Brunini, Adrian JO - Monthly Notices of the Royal Astronomical Society VL - 291 Y1 - 1997/11/1 SP - L47 KW - EXTRASOLAR PLANETS/ BINARY STARS/ SOLAR ORBITS/ CENTER OF MASS/ STELLAR LUMINOSITY/ PLANETARY SYSTEMS/ DIGITAL SIMULATION/ ELLIPTICAL ORBITS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997MNRAS.291L..47B&db_key=AST&high=42a068d47505393 N2 - We discuss the possibility of the presence of planetary bodies orbiting BD + 31deg643. We show that, beyond 1000 au from the center of mass of the binary system, the presence of planetary embryos in the recently discovered circumbinary disk is possible. We also show that the central depletion observed in the disk structure is a result of the tidal interaction with the binary. ER - TY - Journal T1 - Beta Pictoris: its evolutionary status A1 - Brunini, A. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 283 Y1 - 1996/12/1 SP - L84 EP - L88 KW - CIRCUMSTELLAR MATTER/ STARS: EVOLUTION/ STARS: INDIVIDUAL: BETAPIC/ PLANETARY SYSTEMS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996MNRAS.283L..84B&db_key=AST&high=42a068d47505393 N2 - Since the discovery of a large infrared excess in betaPic, this star has been intensively studied, and is currently considered as one of the best candidates for being the centre of an extrasolar planetary system. Such a star will be surrounded by an asymmetric, edge-on dust disc extending beyond 10^3 au from the star. The suspected existence of a planetary system around betaPic has recently been strongly reinforced by the discovery of a central cleared zone about 40 au from the star. A disc warp has also been detected, the most straightforward explanation of which is the presence of at least a giant planet orbiting betaPic. Further evidence comes from the low gas-to-dust ratio, which may be due to the planetary system formation process. Redshifted and highly variable circumstellar absorption lines of several ions have been interpreted as resulting from the evaporation of comets falling on to betaPic. Recently, the very existence of the dust disc was employed to attribute a small age to betaPic. However, the amount of dust produced by the evaporating comets has been shown to be sufficient to replenish the disc, making the arguments in favour of small ages no longer meaningful. In the frame of the cometary hypothesis, we show that the analysis of the rate of events that would have been observed in the Solar system at different evolutionary stages argues in favour of a large age for betaPic. However, the estimation of stellar ages employing cometary fluxes should be treated with caution, on account of the diversity of possible planetary systems. We also present a new analysis of the evolutionary status of betaPic in the framework of stellar evolution, showing that, with the present uncertainties, there is a continuum of possible ages for this star. However, employing the data deduced from the cometary flux, we obtain a consistent scenario of a large stellar age. ER - TY - Journal T1 - Capture conditions in restricted three-body problem. A1 - Brunini, A. A1 - Giordano, C. M. A1 - Orellana, R. B. JO - Astronomy and Astrophysics VL - 314 Y1 - 1996/10/1 SP - 977 EP - 982 KW - CELESTIAL MECHANICS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...314..977B&db_key=AST&high=42a068d47505393 N2 - The capture regions for planetary satellites are numerically explored in the frame of the restricted tree-body problem. Appropriate scaling relations for describing capture conditions in terms of mu are provided in the bidimensional problem. Also the tridimensional problem is considered and capture regions completely characterized for Jupiter, Uranus and the Earth. A discussion is given of conditions leading to capture when the planetary eccentricity is taken into account. ER - TY - Journal T1 - Perturbations on an extended Kuiper disk caused by passing stars and giant molecular clouds. A1 - Brunini, A. A1 - Fernandez, J. A. JO - Astronomy and Astrophysics VL - 308 Y1 - 1996/4/1 SP - 988 EP - 994 KW - CELESTIAL MECHANICS/ CIRCUMSTELLAR MATTER/ COMETS/ DISKS/ PLANETARY SYSTEMS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...308..988B&db_key=AST&high=42a068d47505393 N2 - We assess the importance of stellar and giant molecular cloud perturbations on extended Kuiper-like disks. We integrate numerically the equations of motion assuming circular orbits for the test Kuiper-disk particles and that the external perturber (either a star or a GMC) moves on a straight path. GMCs are modeled as very diffuse structures with a few dense clumps of 10^3^M_sun_, so the bulk of a GMC perturbation is assumed to arise from the sum of the contributions of independent encounters with the dense clumps. We find that external perturbers can induce eccentricities of about 0.04-0.08 over the solar system age on Kuiper-disk objects in initially circular orbits of radii 100-500AU. Relative changes of the semimajor axis are of the same order, thus allowing radial excursions of some tens AU. This migh have important consequences in the accretion process and in the collisional evolution of Kuiper-disk members. Furthermore, due to small radial excursions, Kuiper-disk objects closer to the planetary region can be injected into chaotic zones. Changes in the orbital inclinations are of a few degrees, thus having little consequence on the flattened structure of the disk. Perturbations by GMCs are found to be much smaller than those caused by passing stars. Yet, the much faster increase of the GMC perturbations with the semimajor axis, ensures that they will become dominant at Oort cloud distances, in agreement with some previous results by different authors. We find a non-zero probability (a few tenths percent) of dynamical disruption of the outer portions of circumstellar disks (say at radii >500AU) over the solar system age. ER - TY - Journal T1 - On the Satellite Capture Problem Capture and stability regions for planetary satellites A1 - Brunini, Adrian JO - Celestial Mechanics and Dynamical Astronomy VL - 64 Y1 - 1996/1/1 SP - 79 EP - 92 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996CeMDA..64...79B&db_key=AST&high=42a068d47505393 N2 - Not Available ER - TY - Journal T1 - Capture of Planetesimals by the Giant Planets A1 - Brunini, Adrian A1 - Conicet, Profoeg JO - Earth Moon and Planets VL - 71 Y1 - 1995/12/1 SP - 281 EP - 284 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995EM%26P...71..281B&db_key=AST&high=42a068d47505393 N2 - Not Available ER - TY - Journal T1 - Numerical Exploration of the Dynamics of Self-Adjoint S-Type Riemann Ellipsoids A1 - Brunini, A. A1 - Giordano, C. M. A1 - Plastino, A. R. JO - Astrophysics and Space Science VL - 234 Y1 - 1995/12/1 SP - 153 EP - 167 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Ap%26SS.234..153B&db_key=AST&high=42a068d47505393 N2 - Not Available ER - TY - Journal T1 - A possible constraint to Uranus' great collision A1 - Brunini, Adrian JO - Planetary and Space Science VL - 43 Y1 - 1995/8/1 SP - 1019 EP - 1021 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995P%26SS...43.1019B&db_key=AST&high=42a068d47505393 N2 - Not Available ER - TY - Journal T1 - The effect of distant stellar encounters on planetary systems. II. A1 - Brunini, A. JO - Astronomy and Astrophysics VL - 293 Y1 - 1995/1/1 SP - 935 EP - 940 KW - CELESTIAL MECHANICS/ STELLAR DYNAMICS/ COMETS: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...293..935B&db_key=AST&high=42a068d47505393 N2 - In this paper, we present an algorithm to assess the importance of distant encounters on planetary and binary systems of arbitrary eccentricity. We also apply this formalism, to evaluate the degree of thermalization of the Kuiper cometary belt, where the use of the impulsive approximation is no longer justified. We found that random passing stars almost completely thermalize the belt beyond some 10^3^ AU from the Sun. ER - TY - Journal T1 - A New Ionosphere Monitoring Technology Based on GPS A1 - Brunini, Claudio A1 - Meza, Amalia A1 - Azpilicueta, Francisco A1 - van Zele, María Andrea A1 - Gende, Mauricio A1 - Díaz, Alejandro JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 415 EP - 429 KW - GPS/ ionosphere/ global ionospheric maps UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..415B&db_key=AST&high=42a068d47506782 N2 - Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earth's horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a `virtual observatory' managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing. ER - TY - Journal T1 - Quiet and perturbed ionospheric representation according to the electron content from GPS signals A1 - Brunini, Claudio A1 - Van Zele, María Andrea A1 - Meza, Amalia A1 - Gende, Mauricio JO - Journal of Geophysical Research (Space Physics) VL - 108b Y1 - 2003/2/1 EP - 1 KW - Ionosphere: Modeling and forecasting/ Ionosphere: Ionospheric disturbances/ Radio Science: Signal processing/ Radio Science: Tomography and imaging/ Radio Science: Instruments and techniques/ UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003JGRA.108b.SIA4B&db_key=AST&high=42a068d47506782 N2 - Signals from Global Positioning System (GPS) satellites received at the surface of the Earth have passed through the terrestrial atmosphere and are therefore affected by refraction in the ionosphere. A large number of permanent dual frequencies GPS tracking stations have been built up in the last years and their data have proved to be suitable to study the ionosphere. The main goal of this paper is to assess the capability of these observations to continuously and routinely monitor the ionosphere at a global scale. The interest was focused on retrieving the coefficients of a spherical harmonics expansion that describe the global distribution of the vertical total electron content (VTEC) from the GPS signal. To test our results, we compare them with other GPS-derived results, with VTEC values computed with the International Reference Ionosphere (IRI-95) model, and with direct VTEC determinations provided by Topex-Poseidon satellite. A large set of global VTEC maps with a time resolution of 2 hours was used to describe the evolution of this ionospheric variable at quiet geomagnetic periods during the year 1997. The outstanding features of the VTEC during the 15 May 1997 geomagnetic storm have also been studied. The results show that our method is able to identify large-scale features and seasonal variations of the VTEC in quiet conditions, as well as its variations during a large geomagnetic storm. ER - TY - Journal T1 - CCD-Based Astrometric Measurement of Photographic Plates A1 - Bustos Fierro, I. H. A1 - Calderón, J. H. JO - Revista Mexicana de Astronomia y Astrofisica VL - 39 Y1 - 2003/1/1 SP - 303 EP - 310 KW - Astrometry/ Carte du Ciel/ Method: block-adjustment/ Open Clusters: individual (NGC587)/ Photographic Astrometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003RMxAA..39..303B&db_key=AST&high=42a068d47508921 N2 - We have developed a methodology for the astrometric measurement of photographic plates making use of a CCD camera. In order to measure a complete 2Â°x 2Â° plate a mosaic of 8×8 frames with 50% overlap in both coordinates was taken. The detection and centering of stellar images was performed with SExtractor, and by means of our own software triple exposures were identified. A noticeable radial distortion produced by the optical system was found and corrected. The reduction to celestial coordinates was performed by means of the block-adjustment technique, using Tycho-2 as reference catalog. Differences with Tycho-2 suggest that the errors of CCD-based positions obtained from the CdC plate are between 0. and 0.. Completeness of the catalogs obtained is also discussed. ER - TY - Journal T1 - Small Field CCD Astrometry with a Long Focus Reflector Telescope A1 - Bustos Fierro, I. H. A1 - Calderón, J. H. JO - Revista Mexicana de Astronomia y Astrofisica VL - 38 Y1 - 2002/10/1 SP - 215 EP - 224 KW - Astrometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002RMxAA..38..215B&db_key=AST&high=42a068d47508921 N2 - We discuss the use of the block adjustment method for determining astrometric positions from a mosaic of CCD frames taken with a long focus reflector telescope. The observations cover an area of 25 arcmin × 25 arcmin around the open cluster Rup21. The source of reference positions was the Tycho-2 Catalogue. The internal error in the measured positions is analyzed, and the external error is estimated from comparison with the Tycho-2 and USNO-A2.0 catalogs. In this comparison it is found that direct CCD images taken with a focal reducer could be distorted by severe field curvature. The effect of distortion presumably introduced by the focal reducer is eliminated with suitable corrections to stellar positions measured on every frame, but a new systematic effect on scales of the entire field is observed. This effect is modeled with polynomials. The final positions have an accuracy of around 0''.15. ER - TY - Journal T1 - Evaluation by Numerical Simulations of the Block Adjustment Method in Small Field CCD Astrometry A1 - Bustos Fierro, I. H. A1 - Calderón, J. H. JO - Revista Mexicana de Astronomia y Astrofisica VL - 36 Y1 - 2000/10/1 SP - 89 EP - 96 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000RMxAA..36...89B&db_key=AST&high=42a068d47508921 N2 - The determination of astrometric positions from a mosaic of direct CCD frames with partial overlap taken with a long focus reflector telescope and the block adjustment technique for data reduction are proposed. The influence of errors introduced by: the measurement method itself, instruments, image centering, and reference positions is evaluated by means of numerical simulations. Finally the achievable accuracy in a 25 arcmin square field covered with sixteen frames is determined. It is found that errors introduced by the method itself and the reference catalog lead to positions with accuracy the same order than the reference catalog. Since errors are not significant if the ACT Reference Catalog is the source of reference positions, this method could be used in a measurement of second epoch positions for the determination of proper motions using Carte du Ciel plates as first epoch. It is also found that errors of the measured positions are dominated by aberrations of optical system and centering error of stellar images. ER - TY - Journal T1 - The Digital Archive of the Photographic Images of the Córdoba Observatory Plates Collections A1 - Calderón, J. H. A1 - Calderón, J. H. A1 - Bustos Fierro, I. H. A1 - Bustos Fierro, I. H. A1 - Melia, R. A1 - Willimoës, C. A1 - Willimoës, C. A1 - Giuppone, C. A1 - Giuppone, C. JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 345 EP - 351 KW - plates archiving/ plates collections/ plates digitization/ astronomy UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..345C&db_key=AST&high=42a068d47511849 N2 - The astronomical events registered in photographic plates are unique. A remarkable interest in using old plates in many areas of the current astronomical research is widely recognized by the IAU. There are almost ten thousand plates in several collections at the Córdoba Observatory and most of them are nearly one century old. This photographic material is difficult to handle in order to get the information stored in it. The goal of this project is to make a digital archive of images of these collections. In this first survey plates are being scanned with a standard commercial transparency scanner. These low spatial resolution, low digital resolution and low signal-to-noise ratio images are intended for facilitating handling and visual inspection. However, one arc-second positions can be obtained. Photometric quality has not been yet determined. Otherwise high quality digital images can be acquired with a microdenstitometer based on a scientific grade CCD whose implementation is at its final stage. The possibility of using a better-performance scanner is being evaluated. It is planned to permit the access to low-resolution images via internet. High-resolution images of selected zones will be available upon request. At this first stage, collections totally digitized at low resolution are:Carte du Ciel and Small Magellanic Cloud Zones. Gaviola's Eta Carinae Spectra and Pulkovo Zones are still in process. ER - TY - Journal T1 - CCD-Based Astrometric Measurement of Photographic Plates A1 - Bustos Fierro, I. H. A1 - Calderón, J. H. JO - Revista Mexicana de Astronomia y Astrofisica VL - 39 Y1 - 2003/1/1 SP - 303 EP - 310 KW - Astrometry/ Carte du Ciel/ Method: block-adjustment/ Open Clusters: individual (NGC587)/ Photographic Astrometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003RMxAA..39..303B&db_key=AST&high=42a068d47511849 N2 - We have developed a methodology for the astrometric measurement of photographic plates making use of a CCD camera. In order to measure a complete 2Â°x 2Â° plate a mosaic of 8×8 frames with 50% overlap in both coordinates was taken. The detection and centering of stellar images was performed with SExtractor, and by means of our own software triple exposures were identified. A noticeable radial distortion produced by the optical system was found and corrected. The reduction to celestial coordinates was performed by means of the block-adjustment technique, using Tycho-2 as reference catalog. Differences with Tycho-2 suggest that the errors of CCD-based positions obtained from the CdC plate are between 0. and 0.. Completeness of the catalogs obtained is also discussed. ER - TY - Journal T1 - Small Field CCD Astrometry with a Long Focus Reflector Telescope A1 - Bustos Fierro, I. H. A1 - Calderón, J. H. JO - Revista Mexicana de Astronomia y Astrofisica VL - 38 Y1 - 2002/10/1 SP - 215 EP - 224 KW - Astrometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002RMxAA..38..215B&db_key=AST&high=42a068d47511849 N2 - We discuss the use of the block adjustment method for determining astrometric positions from a mosaic of CCD frames taken with a long focus reflector telescope. The observations cover an area of 25 arcmin × 25 arcmin around the open cluster Rup21. The source of reference positions was the Tycho-2 Catalogue. The internal error in the measured positions is analyzed, and the external error is estimated from comparison with the Tycho-2 and USNO-A2.0 catalogs. In this comparison it is found that direct CCD images taken with a focal reducer could be distorted by severe field curvature. The effect of distortion presumably introduced by the focal reducer is eliminated with suitable corrections to stellar positions measured on every frame, but a new systematic effect on scales of the entire field is observed. This effect is modeled with polynomials. The final positions have an accuracy of around 0''.15. ER - TY - Journal T1 - Evaluation by Numerical Simulations of the Block Adjustment Method in Small Field CCD Astrometry A1 - Bustos Fierro, I. H. A1 - Calderón, J. H. JO - Revista Mexicana de Astronomia y Astrofisica VL - 36 Y1 - 2000/10/1 SP - 89 EP - 96 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000RMxAA..36...89B&db_key=AST&high=42a068d47511849 N2 - The determination of astrometric positions from a mosaic of direct CCD frames with partial overlap taken with a long focus reflector telescope and the block adjustment technique for data reduction are proposed. The influence of errors introduced by: the measurement method itself, instruments, image centering, and reference positions is evaluated by means of numerical simulations. Finally the achievable accuracy in a 25 arcmin square field covered with sixteen frames is determined. It is found that errors introduced by the method itself and the reference catalog lead to positions with accuracy the same order than the reference catalog. Since errors are not significant if the ACT Reference Catalog is the source of reference positions, this method could be used in a measurement of second epoch positions for the determination of proper motions using Carte du Ciel plates as first epoch. It is also found that errors of the measured positions are dominated by aberrations of optical system and centering error of stellar images. ER - TY - Journal T1 - Kinetic electrons in high-speed solar wind streams: Formation of high-energy tails A1 - Lie-Svendsen, Øystein A1 - Hansteen, Viggo H. A1 - Leer, Egil JO - Journal of Geophysical Research VL - 102 Y1 - 1997/3/1 SP - 4701 EP - 4718 KW - Interplanetary Physics: Solar wind plasma/ Interplanetary Physics: Sources of the solar wind/ Solar Physics/ Astrophysics/ and Astronomy: Corona/ Solar Physics/ Astrophysics/ and Astronomy: Coronal holes UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997JGR...102.4701L&db_key=AST&high=42a068d47513573 N2 - We study the evolution of the electron velocity distribution function in high-speed solar wind streams from the collision-dominated corona and into the collisionless interplanetary space. The model we employ solves the kinetic transport equation with the Fokker-Planck collision operator to describe Coulomb collisions between electrons. We use a test particle approach, where test electrons are injected into a prescribed solar wind background. The density, temperature, and electric field associated with the background are computed from fluid models. The test electrons are in thermal equilibrium with the background at the base of the corona, and we study the evolution of the velocity distribution of the test electrons as a function of altitude. We find that velocity filtration, due to the energy dependence of the Coulomb cross section, is a small effect and is not capable of producing significant beams in the distribution or a temperature moment that increases with altitude. The distribution function is mainly determined by the electric field and the expanding geometry and consists of a population with an almost isotropic core which is bound in the electrostatic potential and a beam-like high-energy tail which escapes. The trapped electrons contribute significantly to the even moments of the distribution function but almost nothing to the odd moments; the drift speed and energy flux moments are carried solely by the tail. In order to describe the high-speed solar wind observed near 0.3 AU by the Helios spacecraft, we use a multifluid model where ions are heated preferentially. The resulting test electron distribution at 0.3 AU, in this background, is in very good agreement with the velocity distributions observed by the Helios spacecraft. ER - TY - Journal T1 - Computational Simulation of Plasmas A1 - Bell, A. R. JO - Astrophysics and Space Science VL - 256 Y1 - 1997/1/1 SP - 13 EP - 35 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997Ap%26SS.256...13B&db_key=AST&high=42a068d47513573 N2 - This paper reviews the use of computational simulation in plasma physics. It describes a range of numerical models varying from particle models of low density collisionless plasmas to fluid models of high density collision-dominated plasmas. Some applications of these models, particularly to laser-produced and astrophysical plasmas, are described. ER - TY - Journal T1 - A Very Large Array 3.6 Centimeter Continuum Survey of Galactic Wolf-Rayet Stars A1 - Cappa, C. A1 - Goss, W. M. A1 - van der Hucht, K. A. JO - Astronomical Journal VL - 127 Y1 - 2004/5/1 SP - 2885 EP - 2897 KW - radio continuum: stars/ Stars: Mass Loss/ Stars: Wolf-Rayet UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127.2885C&db_key=AST&high=42a068d47515088 N2 - We report the results of a survey of radio continuum emission of Galactic Wolf-Rayet (WR) stars north of delta=-46°. The observations were obtained at 8.46 GHz (3.6 cm) using the Very Large Array, with an angular resolution of ~6"×9" and typical rms noise of ~0.04 mJy beam^-1. Our survey of 34 WR stars resulted in 15 definite and five probable detections, 13 of these for the first time at radio wavelengths. All detections are unresolved (theta<~5"). Time variations in flux are confirmed in the cases of WR 98a, 104, 105, and 125. WR 79a and WR 89 are also variable in flux, and we suspect they are also nonthermal emitters. Thus, of our sample 20%-30% of the detected stars are nonthermal emitters. Average mass-loss rate determinations obtained excluding definite and suspected nonthermal cases give similar values for WN (all subtypes) and WC5-7 stars [M(WN)=(4+/-3)×10^-5 M_solar yr^-1 and M(WC5-7)=(4+/-2)×10^-5 M_solar yr^-1], while a lower value was obtained for WC8-9 stars [M(WC8-9)=(2+/-1)×10^-5 M_solar yr^-1]. Uncertainties in stellar distances largely contribute to the observed scatter in mass-loss rates. Upper limits to the mass-loss rates were obtained in cases of undetected sources and for sources that probably show additional nonthermal emission. ER - TY - Journal T1 - An H I interstellar bubble linked to the O-type stars BD +24^or 3866 and BD +25^or 3952 A1 - Cappa, C. A1 - Pineault, S. A1 - Arnal, E. M. A1 - Cichowolski, S. JO - Astronomy and Astrophysics VL - 395 Y1 - 2002/12/1 SP - 955 EP - 967 KW - ISM: bubbles/ HII regions/ ISM: individual objects: Sh2-88/ Sh2-87/ G61.7+0.9/ stars: early-type/ stars: individual: BD +24or 3866/ BD +24or 3881/ BD +25or 3952 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...395..955C&db_key=AST&high=42a068d47515088 N2 - We investigate the ISM in the vicinity of the O-type stars BD +24^or 3866 (O8.5II(f)), BD +24^or 3881 (O6.5III(f)) and BD +24^or 3952 (O8) based on radio continuum and HI line data obtained with the Synthesis Telescope of the Dominion Radio Astrophysical Observatory (DRAO) with synthesized beams of 1\farcm 5 and 7\arcmin at 1420 and 408 MHz, respectively. High angular resolution IRAS data (HIRES) are also analyzed. BD +24^or 3866 is found to be located close to the inner border of a slowly expanding shell. The evolved HII region Sh2-88, which is excited by BD +25^or 3952, appears to be interacting with neutral material in the approaching part of this shell. The whole structure is at a distance of 2.4 kpc and is about 23x15 pc in radius. The total swept up mass is 1300 M_sun. The stellar winds of BD +24^or 3866 and BD +25^or 3952, are mainly responsible for shaping the HI structure. An HI expanding shell was also found to be related to the HII region G61.7+0.9. At a kinematic distance of 2.4 kpc, this feature is 10 pc in radius and has neutral and ionized masses of 200 and 135 M_sun, respectively. The present observational data do not allow us to identify a definite interstellar HI feature associated with BD +24^or 3881. We consider different explanations for this fact. ER - TY - Journal T1 - VLA Radio Continuum and IRAS Observations of the Ring Nebulae around WR 101 and WR 113 A1 - Cappa, C. E. A1 - Goss, W. M. A1 - Pineault, S. JO - Astronomical Journal VL - 123 Y1 - 2002/6/1 SP - 3348 EP - 3355 KW - ISM: Bubbles/ ISM: individual (Anon. WR 101)/ ISM: individual (Anon WR 113)/ Stars: Individual: Alphanumeric: WR 101/ Stars: Individual: Alphanumeric: WR 113/ Stars: Wolf-Rayet UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123.3348C&db_key=AST&high=42a068d47515088 N2 - We report radio continuum observations at 1465 MHz obtained with the Very Large Array (VLA) in the DnC configuration toward the ring nebulae associated with the stars WR 101 and WR 113, with resolutions of ~38" and 30", respectively. IRAS images of the nebulae with resolutions of about 2' (90 M_solar, 40 cm^-3) are also analyzed. A remarkable resemblance among the optical, infrared, and radio images of these ring nebulae is observed. The VLA data indicate that Anon. WR 101 is thermal in nature. An ionized mass of ~230+/-40 M_solar and electron densities in the range ~40-55 cm^-3 were estimated for Anon. WR 101. The derived ionized masses and electron densities in the inner and outer shells of the nebula related to WR 113 are ~20+/-10 M_solar, 180-500 cm^-3 and ~90 M_solar 40 cm^-3, respectively. Based on infrared data at 60 and 100 mum, the derived masses and temperatures for the dust component in the ring nebula around WR 101 are 0.3-1 M_solar and ~40 K. The associated masses suggest that the ring nebula related to WR 101 and the outer arc associated with WR 113 consist of swept-up interstellar matter, while the relatively low ionized mass associated with the inner shell of the nebula around WR 113 may contain a nonnegligible contribution of expelled ejecta material. The derived electron densities for the nebula around WR 101 and the inner shell around WR 113 are comparable to electron densities for other W-R ring nebulae. Low filling factors are inferred for both nebulae. The nebulae probably originated during the current W-R phase of the stars. ER - TY - Journal T1 - CO Observations of NGC 2359: The Molecular Clouds Revisited A1 - Cappa, C. E. A1 - Rubio, M. A1 - Goss, W. M. JO - Astronomical Journal VL - 121 Y1 - 2001/5/1 SP - 2664 EP - 2672 KW - ISM: Bubbles/ ISM: Molecules/ ISM: Individual: NGC Number: NGC 2359/ Stars: Individual: Henry Draper Number: HD 56925/ Stars: Wolf-Rayet UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121.2664C&db_key=AST&high=42a068d47515088 N2 - Based on CO (2-1) observations obtained with the Swedish-ESO Submillimeter Telescope, the distribution of molecular material associated with the Wolf-Rayet ring nebula NGC 2359 has been determined. The angular resolution is 22", and the velocity resolution is 0.33 km s^-1. Three molecular components are detected in the direction of the nebula. The bulk of the molecular gas is observed at 54 km s^-1 and follows the southeastern border of the nebula. Adopting a distance d=5 kpc for NGC 2359, an H₂ mass of about 1200+/-500 M_solar appears to be related to the southern part of the nebula, while 140+/-50 M_solar are linked to the filamentary windblown bubble. The volume density of the molecular gas related to the southern bar is >=10³ H₂ molecules cm^-3, while lower densities were estimated for the material associated with the filamentary windblown bubble. From the present data, it is not clear if the molecular gas at 37 km s^-1 (~=380+/-120 M_solar, d=5 kpc) is associated with the nebula, but the molecular material observed at 67 km s^-1 (~=70+/-25 M_solar, d=5 kpc) seems to be unconnected. The comparison between ionized, H I, and molecular distributions indicates that the H I filament detected with the Very Large Array is located at the interface between the ionized and molecular material, and that the H I filament at 54 km s^-1 has originated in the photodissociation of the H₂. Most of the molecular gas associated with the filamentary bubble seems to be interstellar in origin. The dynamics of the nebula is reanalyzed based on these new molecular results. It is consistent with either momentum conservation or an intermediate stage between energy and momentum conservation. ER - TY - Journal T1 - A Search for Interstellar Bubbles surrounding Massive Stars in Perseus OB1 A1 - Cappa, C. E. A1 - Herbstmeier, Uwe JO - Astronomical Journal VL - 120 Y1 - 2000/10/1 SP - 1963 EP - 1973 KW - ISM: Bubbles/ ISM: individual (Perseus OB1)/ Stars: Early-Type/ stars: individual UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....120.1963C&db_key=AST&high=42a068d47515088 N2 - We have examined the interstellar medium in the vicinity of massive stars belonging to the Per OB1 association based on neutral hydrogen 21 cm observations obtained with the 100 m radio telescope at Effelsberg (HPBW=8.4') and complementary data from the Leiden-Dwingeloo H I Survey (HPBW=36'). The higher angular resolution H I observations allowed us to discover probable wind-blown bubbles related to four massive stars in the association, namely, HD 14442 [O5n(f)p], HD 14947 [O5If+], HD 13022 [O9.5II-III((n))], and HD 13338 [O9.5V], while the detection of a wind-blown bubble associated with HD 16691 [O5If+] is less conclusive. A clear H I shell coincident in position with two B1III stars (HD 15233 and Hilt 311) was also detected. Some of these features also have infrared and/or molecular counterparts. The energetics of the structures related to each massive star is analyzed. The new H I interstellar bubbles appear to be similar to the ones found surrounding Wolf-Rayet stars and other Of stars. The large-scale maps obtained using the lower angular resolution H I data show that most of the early-type stars belonging to Per OB1 are placed in a region of low H I emission. The association could have blown a H I shell of about 350×550 pc in size. This large H I shell has an infrared counterpart. ER - TY - Journal T1 - A Study of Neutral and Ionized Gas of the Wolf-Rayet Ring Nebula NGC 2359 A1 - Cappa, C. E. A1 - Goss, W. M. A1 - Niemela, V. S. A1 - Ostrov, P. G. JO - Astronomical Journal VL - 118 Y1 - 1999/8/1 SP - 948 EP - 959 KW - ISM: BUBBLES/ ISM: INDIVIDUAL (NGC 2359)/ STARS: INDIVIDUAL (HD 56925)/ STARS: WOLF-RAYET UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....118..948C&db_key=AST&high=42a068d47515088 N2 - Based on H I 21 cm line and radio continuum observations performed with the Very Large Array of the National Radio Astronomy Observatory and on optical narrowband images obtained at the Cerro Tololo Inter-American Observatory, we investigate the distribution of the ionized and neutral gas in the region of the ring nebula NGC 2359 surrounding the Wolf-Rayet star HD 56925 at a distance of 5 kpc. The radio continuum data, obtained at 1465 MHz with an angular resolution of ~30", have the same morphology as the optical Halpha nebular line emission. An ionized mass of 70 M_solar and an electron density (corrected for filling factor) of 120 cm^-3 were estimated for the filamentary shell, while the mass in the whole ionized complex is in the range 850-1100 M_solar. The H I 21 cm line data, with angular and velocity resolutions of ~45" and 1.3 km s^-1, respectively, reveal for the first time neutral hydrogen clearly interacting with the optical ring nebula at its systemic velocity of 54 km s^-1 and at 63 km s^-1. The H I gas distribution at 54 km s^-1 indicates the location of the ionization fronts. The estimated total neutral mass is ~320 M_solar. Most of this mass seems to be located in a hemispherical shell expanding at 6-7 km s^-1. Taking into account the ionized, neutral, and molecular components, the mass associated with the NGC 2359 complex is about 2200 M_solar. The dynamics of the nebula are consistent with momentum conservation or with an intermediate stage between energy and momentum conservation. ER - TY - Journal T1 - The Interstellar Medium in the Environs of O-Type Stars A1 - Cappa, Cristina E. A1 - Benaglia, Paula JO - Astronomical Journal VL - 116 Y1 - 1998/10/1 SP - 1906 EP - 1914 KW - ISM: BUBBLES/ STARS: EARLY-TYPE/ STARS: INDIVIDUAL (HD 112244)/ STARS: INDIVIDUAL (HD 155913)/ STARS: INDIVIDUAL (HD 175754)/ STARS: INDIVIDUAL (HD 175876) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116.1906C&db_key=AST&high=42a068d47515088 N2 - We analyze the distribution of the neutral gas in the neighborhood of four southern O-type stars based on observations of the 21 cm H i line. These data disclose H i bubbles probably associated with the stars HD 112244 [O8.5Iab(f)], HD 155913 [O5Vn((f))], HD 175754 [O8II((f))], and HD 175876 [O6.5III(n)(f)]. The dimensions of these bubbles are in the range 90 to 170 pc, and their expansion velocities are low, about 10 km s^-1, implying dynamical ages of (3-6) x 10^6 yr. Only a few percent of the mechanical energy of the stellar wind is transformed into kinetic energy of the shells. Their origin and the contribution of other early-type stars to the formation of these bubbles are discussed. Particularly, it is suggested that HD 155913 belongs to an unknown OB association that could also have contributed in the formation of the H i bubble surrounding this star. These new H i bubbles resemble H i bubbles surrounding Wolf-Rayet (W-R) stars. The presence of stellar wind bubbles associated with O-type stars supports an interpretation where the massive progenitors of the W-R stars are also responsible for the formation of the H i bubbles detected around W-R stars. ER - TY - Journal T1 - The Interaction of NGC 6888 and HD 192163 With the Surrounding Interstellar Medium A1 - Cappa, Cristina E. A1 - Dubner, Gloria M. A1 - Rogers, Chris A1 - St-Louis, Nicole JO - Astronomical Journal VL - 112 Y1 - 1996/9/1 SP - 1104 KW - STARS: WOLF-RAYET/ STARS: KINEMATICS/ ISM: KINEMATICS AND DYNAMICS/ STARS: INDIVIDUAL: HD 192163 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996AJ....112.1104C&db_key=AST&high=42a068d47515088 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1104C&db_key=AST ER - TY - Journal T1 - The HI bubble surrounding the Wolf-Rayet star WR149. A1 - Cappa, C. E. A1 - Niemela, V. S. A1 - Herbstmeier, U. A1 - Koribalski, B. JO - Astronomy and Astrophysics VL - 312 Y1 - 1996/8/1 SP - 283 EP - 288 KW - ISM: BUBBLES/ STARS: INDIVIDUAL: WR149/ STARS: WOLF-RAYET/ RADIO LINES: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...312..283C&db_key=AST&high=42a068d47515088 N2 - Neutral hydrogen 21-cm observations obtained with the 100-m Effelsberg telescope have disclosed a HI bubble surrounding the WN6-7 star WR149, located in the far side of the Perseus spiral arm. With a radius of 57pc and an expansion velocity of about 10km/s, this new bubble appears similar to those previously found around other Wolf-Rayet stars. Since stars of WN6-7 spectral sub-type are often found in open clusters and associations, we suggest that the observed HI bubble may be related to an undetected OB association. A second HI void in the neighbourhood is briefly discussed. ER - TY - Journal T1 - Chaotic Orbits in Galactic Satellites A1 - Carpintero, D. D. A1 - Muzzio, J. C. A1 - Vergne, M. M. A1 - Wachlin, F. C. JO - Celestial Mechanics and Dynamical Astronomy VL - 85 Y1 - 2003/3/1 SP - 247 EP - 267 KW - galactic satellites/ stellar orbits/ chaotic motion UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003CeMDA..85..247C&db_key=AST&high=42a068d47516352 N2 - In several previous papers we had investigated the orbits of the stars that make up galactic satellites and found that many of those orbits were chaotic. In those investigations we made extensive use of the frequency analysis method of Carpintero and Aguilar (1998) to classify the orbits, because that method is much faster than the use of Lyapunov exponents, allows the classification of the regular orbits and our initial comparison of both methods had shown excellent agreement between their results. More recently, we have found some problems with the use of frequency analysis in rotating systems, so that here we present a new investigation of orbits inside galactic satellites using exclusively Lyapunov exponents. Some of our previous conclusions are confirmed, while others are altered. Besides, the Lyapunov times that are now obtained show that the time scales of the chaotic processes are shorter than, or comparable to, other time scales characteristic of galactic satellites. ER - TY - Journal T1 - Regular and Chaotic Motion in Globular Clusters A1 - Carpintero, Daniel D. A1 - Muzzio, Juan C. A1 - Wachlin, Felipe C. JO - Celestial Mechanics and Dynamical Astronomy VL - 73 Y1 - 1999/1/1 SP - 159 EP - 168 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999CeMDA..73..159C&db_key=AST&high=42a068d47516352 N2 - As a first step towards a comprehensive investigation of stellar motions within globular clusters, we present here the results of a study of stellar orbits in a mildly triaxial globular cluster that follows a circular orbit inside a galaxy. The stellar orbits were classified using the frequency analysis code of Carpintero and Aguilar and, as a check, the Liapunov characteristic exponents were also computed in some cases. The orbit families were obtained using different start spaces. Chaotic orbits turn out to be very common and while, as could be expected, they are particularly abundant in the outer parts of the cluster, they are still significant in the innermost regions. Their relevance for the structure of the cluster is discussed. ER - TY - Journal T1 - Orbit classification in arbitrary 2D and 3D potentials A1 - Carpintero, Daniel D. A1 - Aguilar, Luis A. JO - Monthly Notices of the Royal Astronomical Society VL - 298 Y1 - 1998/7/1 SP - 1 EP - 21 KW - CELESTIAL MECHANICS/ STELLAR DYNAMICS/ GALAXIES: KINEMATICS AND DYNAMICS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998MNRAS.298....1C&db_key=AST&high=42a068d47516352 N2 - A method of classifying generic orbits in arbitrary 2D and 3D potentials is presented. It is based on the concept of spectral dynamics introduced by Binney & Spergel that uses the Fourier transform of the time series of each coordinate. The method is tested using a number of potentials previously studied in the literature and is shown to distinguish correctly between regular and irregular orbits, to identify the various families of regular orbits (boxes, loops, tubes, boxlets, etc.), and to recognize the second-rank resonances that bifurcate from them. The method returns the position of the potential centre and, for 2D potentials, the orientation of the principal axes as well, should this be unknown. A further advantage of the method is that it has been encoded in a FORTRAN program that does not require user intervention, except for `fine tuning' of search parameters that define the numerical limits of the code. The automatic character makes the program suitable for classifying large numbers of orbits. ER - TY - Journal T1 - Radial orbit instability in a Hubble-expanding universe A1 - Carpintero, Daniel D. A1 - Muzzio, Juan C. JO - Astrophysical Journal VL - 440 Y1 - 1995/2/1 SP - 5 EP - 21 KW - ASTRONOMICAL MODELS/ COSMOLOGY/ GALACTIC EVOLUTION/ GALACTIC HALOS/ GRAVITATIONAL COLLAPSE/ HUBBLE CONSTANT/ STELLAR ORBITS/ SYSTEMS STABILITY/ UNIVERSE/ COMPUTERIZED SIMULATION/ GALACTIC MASS/ MATHEMATICAL MODELS/ RADIAL DISTRIBUTION/ STELLAR SYSTEMS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ApJ...440....5C&db_key=AST&high=42a068d47516352 N2 - We investigate the role of the radial orbit instability in the formation of galactic halos through dissipationless collapse. We present numerical simulations where both the Hubble expansion and the inhomogeneities of the protogalactic material have been taken into account. We find that the radial orbit instability is a transient effect for a wide variety of initial conditions, including those with cosmological-like density fluctuations, as a result of the combination of two effects: the inhomogeneities give rise to condensations whose interactions introduce tangential motions, and the Hubble expansion delays the collapse long enough for those motions to grow, preventing the instability. We conclude that, with reasonable initial conditions, the end product of a dissipationless collapse does not need to be a triaxial system. ER - TY - Journal T1 - Letter: An Exact Solution for the Fluctuations of an FRW Cosmology with n Scalar Fields, for an Arbitrary Potential A1 - Castagnino, Mario A1 - Chavarriga, Javier A1 - Lara, Luis JO - General Relativity and Gravitation VL - 35 Y1 - 2003/8/1 SP - 1495 EP - 1501 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GReGr..35.1495C&db_key=AST&high=42a068d47517886 N2 - In this work we rigorously study the fluctuations in FRW models coupled with n neutral scalar fields, minimally coupled to the gravitational field. We find the exact solutions and the asymptotic behavior for the fluctuation around the critical point of the background for an arbitrary potential. ER - TY - Journal T1 - Asymptotic behavior of FRW cosmologies with many scalar fields A1 - Castagnino, Mario A1 - Giacomini, Hector A1 - Lara, Luis JO - Physical Review D VL - 65 Y1 - 2002/1/1 SP - 23509 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002PhRvD..65b3509C&db_key=AST&high=42a068d47517886 N2 - The dynamical evolution of FRW cosmologies conformally coupled to a finite set of scalar fields is studied. The scalar fields interact between them and we also consider a self-interaction term. lt is proved that when k=-1 and k=0 only one physical asymptotic behavior is possible: the radius of the universe expands forever. When k=1 either we have the just described behavior or the universe will ultimately collapse in a finite time. But we also give evidence that an oscillatory chaotic behavior is possible in this case if a fine-tuning between the initial conditions is satisfied. ER - TY - Journal T1 - Qualitative dynamical properties of a spatially closed FRW universe conformally coupled to a scalar field A1 - Castagnino, M. A. A1 - Giacomini, H. A1 - Lara, L. JO - Physical Review D VL - 63 Y1 - 2001/2/1 SP - 44003 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001PhRvD..63d4003C&db_key=AST&high=42a068d47517886 N2 - In this work the dynamics of a spatially closed Friedmann-Robertson-Walker model for the universe conformally coupled to a scalar field is studied. It is proven that this dynamics, formulated in terms of the proper time t (or cosmic time) is very simple. For arbitrary initial conditions, we prove that the universe will ultimately collapse in a finite time. We also show that there is no inflation at any stage of the evolution. When represented in phase space all trajectories of the system are unbounded, owing to a divergence that appears at the singularity, and showing that there is no chaos. ER - TY - Journal T1 - Dynamical properties of the conformally coupled flat FRW model A1 - Castagnino, M. A. A1 - Giacomini, H. A1 - Lara, L. JO - Physical Review D VL - 61 Y1 - 2000/5/1 SP - 107302 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000PhRvD..61j7302C&db_key=AST&high=42a068d47517886 N2 - In this paper we study the dynamical behavior of a simple cosmological model defined by a spatially flat Robertson-Walker geometry, conformally coupled with a massive scalar field. We determine a Lyapunov-like function for the nonlinear evolution equations. From this function we prove that all the stationary solutions are unstable. We also show that all initial conditions, different from the stationary points, originate an expanding universe in the asymptotic regime, with a scale parameter a(t) that goes to infinity and the scalar field phi(t) that goes to zero in an oscillatory way. We also find two asymptotic solutions, valid for sufficiently large values of time. These solutions correspond to a radiation dominated phase and to a matter dominated phase, respectively. ER - TY - Journal T1 - Creation of Unstable Particles and Decoherence in Semiclassical Cosmology A1 - Castagnino, Mario A1 - Landau, Susana A1 - Lombardo, Fernando C. JO - General Relativity and Gravitation VL - 31 Y1 - 1999/9/1 SP - 1407 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999GReGr..31.1407C&db_key=AST&high=42a068d47517886 N2 - We consider a simple cosmological model in order to show the importance of unstable particle creation for the validity of the semiclassical approximation. Using the mathematical structure of rigged Hilbert spaces we show that particle creation is the seed of decoherence which enables the quantum to classical transition. ER - TY - Journal T1 - Mathematical structure of quantum superspace as a consequence of time asymmetry A1 - Castagnino, Mario JO - Physical Review D VL - 57 Y1 - 1998/1/1 SP - 750 EP - 767 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998PhRvD..57..750C&db_key=AST&high=42a068d47517886 N2 - It is demonstrated how a convenient choice of the mathematical structure of the quantum cosmology superspace of the wave functions of the universe, precisely the definition of a convenient regular state superspace and the restriction of the dynamics to this space, yields directly an irreversible evolution, in the classical (and semiclassical) phase of the universe, where decoherence and correlations take place and therefore give origin to a classical universe, the second law of thermodynamics is demonstrated, connection with the Reichenbach branch system idea can be implemented, some rough coincidences with observational data are obtained, the arrows of time can be correlated, and time asymmetry can be explained as a state space asymmetry (e.g., like a spontaneous symmetry breaking). All these facts solve the problem of time asymmetry and show that it is time asymmetry itself that defines the most important features of the mathematical structure of superspace. ER - TY - Journal T1 - The Global Nature of the Arrow of Time and the Bohm-Reichenbach Diagram A1 - Castagnino, M. A. JO - LNP Vol. 504: Irreversibility and Causality VL - 504 Y1 - 1998/1/1 SP - 282 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998LNP...504..282C&db_key=AST&high=42a068d47517886 N2 - Introduction The Arrow of Time Is Global Reichenbach Global System Bohm Diagrams Bohm-Reichenbach Diagram The Quantum Measurement Process The Geometrical Arrow of Time Conclusion ER - TY - Journal T1 - Energy-Momentum and Equivalence Principle in Non-Riemannian Geometries A1 - Castagnino, M. A1 - Levinas, M. L. A1 - Umérez, N. JO - General Relativity and Gravitation VL - 29 Y1 - 1997/6/1 SP - 691 EP - 703 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997GReGr..29..691C&db_key=AST&high=42a068d47517886 N2 - We introduce an energy-momentum density vector which is independent of the affine structure of the manifold and whose conservation is linked to observers. Integrating this quantity over time-like surfaces we can define Hamiltonian and momentum for the system which coincide with the corresponding {ßc adm} definitions for the case of irrotational Riemannian manifolds. As a consequence of our formalism, a Weak Equivalence Principle version for manifolds with torsion appears as the natural extension to non-Riemannian geometries from the Equivalence Principle of General. ER - TY - Journal T1 - Entropy Generation in Cosmological Particle Creation A1 - Castagnino, Mario A. A1 - Gaioli, Fabián H. A1 - Sforza, Daniel M. JO - General Relativity and Gravitation VL - 28 Y1 - 1996/9/1 SP - 1129 EP - 1137 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996GReGr..28.1129C&db_key=AST&high=42a068d47517886 N2 - A very simplified model of the Universe is considered in order to propose an alternative approach to the irreversible evolution of the Universe at very early times. The entropy generation at the quantum stage can be thought as a consequence of an instability of the system. Then particle creation arises from this instability. ER - TY - Journal T1 - Cosmological Features of Time-Asymmetry A1 - Castagnino, M. A. A1 - Gaioli, F. H. A1 - Gunzig, E. JO - Fundamentals of Cosmic Physics VL - 16 Y1 - 1996/1/1 SP - 221 EP - 375 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996FCPh...16..221C&db_key=AST&high=42a068d47517886 N2 - The problem of the arrow of time in the cosmological context is considered within the Friedrichs-Lee model. The fundamental features underlying the irreversible evolution of a system are discussed. A particularly important class of non-integrable systems are the so-called large Poincare systems, which have a continuous spectrum and resonances. The Friedrichs-Lee model above mentioned exhibits the typical behavior of non-integrable and unstable systems. The existence of resonances prevents us from finding solutions analytic in the coupling constant of the eigenvalue problem associated with the Hamiltonian. Divergences can be avoided using an extension of the orthodox quantum mechanics within the frame provided by the rigged Hilbert spaces. By deforming contours of integration we obtain exponential contributions arising from the simple poles of the resolvent on the second sheet. In the special case of the Friedrichs-Lee model, using a formal procedure of analytic continuation, we show that a complete set of eigenvectors of the Hamiltonian can be associated with poles of the resolvent. As a result, the dynamical evolution group is split into two semigroups, one decaying in the future and the other in the past. Irreversibility emerges thus as a spontaneous symmetry breaking. Each semigroup is related to a Hardy class space of functions as test space in the Gel'fand triplet. We also define a Lyapunov variable and formulate a second principle of thermodynamics from the "microphysical irreversible world." Some consequences of this time-asymmetry are briefly discussed and a very schematic cosmological model is presented. ER - TY - Journal T1 - On the shape of luminosity profiles of dwarf galaxies as a distance indicator: The NGC 5044 Group revisited A1 - Cellone, S. A. A1 - Buzzoni, A. JO - Astronomy and Astrophysics VL - 369 Y1 - 2001/4/1 SP - 742 EP - 749 KW - GALAXIES: CLUSTERS: NGC 5044 GROUP/ GALAXIES: DISTANCES AND REDSHIFTS/ ELLIPTICAL AND LENTICULAR/ FUNDAMENTAL PARAMETERS/ PHOTOMETRY/ STRUCTURE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...369..742C&db_key=AST&high=42a068d47520762 N2 - Conflicting evidence has been recently raised in order to use surface brightness profiles of dwarf galaxies as a distance indicator. In this paper we discuss in some detail the main error sources in profile fitting procedures for galaxies with more than one physical component, showing their impact on the resulting shape parameters. The apparent tight coupling between shape parameter and (pseudo) scalelength in the Sérsic law is especially dealt with, demonstrating that this relationship is mostly a mathematical artifact, thus throwing doubts on its usefulness as a distance indicator. Galaxies departing from the luminosity-shape relation are shown to exhibit different kinds of intrinsic peculiarities, thus prompting for better securing the empirical constraints to conform observational samples. As a relevant example in this sense, new observations of the galaxy N50 in the NGC 5044 Group are presented. We show that this object may be at an intermediate evolutionary stage between blue compact dwarfs (BCDs) and dwarf ellipticals (dEs). Based on observations collected at the European Southern Observatory, La Silla (Chile), and the Complejo Astronómico El Leoncito (CASLEO), operated under agreement between CONICET and the Universities of La Plata, Córdoba, and San~Juan (Argentina). ER - TY - Journal T1 - The Incidence of the Host Galaxy in Microvariability Observations of Quasars A1 - Cellone, S. A. A1 - Romero, G. E. A1 - Combi, J. A. JO - Astronomical Journal VL - 119 Y1 - 2000/4/1 SP - 1534 EP - 1541 KW - GALAXIES: PHOTOMETRY/ QUASARS: INDIVIDUAL (PKS 2316-423) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....119.1534C&db_key=AST&high=42a068d47520762 N2 - The incidence of a host galaxy in aperture photometry of active galactic nuclei is studied by means of actual and simulated CCD observations. Our goal is to evaluate the importance of spurious variations, introduced by seeing fluctuations during the observations, in the differential light curves used to study optical microvariability. Repeated CCD observations during two consecutive nights were used to obtain time-resolved aperture photometry for the BL Lac object PKS 2316-423, which is located at the center of a conspicuous elliptical galaxy, and for several field stars. The blazar seems to be variable according to standard variability criteria; however we show that the observed differential magnitude variations are strongly correlated with seeing fluctuations during the nights. Moreover, another galaxy within the same CCD field shows nearly identical variations, clearly indicating that such variations are artifacts of the aperture photometry. Simulated observations of quasars within host galaxies of different morphologies and spanning a wide range of luminosities were also used to evaluate the effects of changing seeing conditions. The results show that spurious differential magnitude variations due to seeing fluctuations are larger for active nuclei within brighter hosts, particularly when small photometric apertures (about the seeing FWHM in radius) are used. According to our results, several recommendations are given to future observers. ER - TY - Journal T1 - Surface brightness profiles of dwarf galaxies in the NGC 5044 Group: A critical revision of the luminosity - shape relation as a distance indicator A1 - Cellone, Sergio A. JO - Astronomy and Astrophysics VL - 345 Y1 - 1999/5/1 SP - 403 EP - 413 KW - GALAXIES: STRUCTURE/ GALAXIES: PHOTOMETRY/ GALAXIES: FUNDAMENTAL PARAMETERS/ GALAXIES: ELLIPTICAL AND LENTICULAR/ CD/ GALAXIES: DISTANCES AND REDSHIFTS/ GALAXIES: CLUSTERS: INDIVIDUAL: NGC 5044 GROUP UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...345..403C&db_key=AST&high=42a068d47520762 N2 - CCD surface photometry of a small sample of dwarf and intermediate luminosity elliptical galaxies in the NGC 5044 Group is presented. Their surface brightness profiles are fitted with a Sérsic law, and it is shown that a few relatively bright galaxies with ``convex'' profiles destroy the known relation between total magnitude and the ``shape'' parameter (N) of the model, thus ruling out the use of this relation as a distance indicator for individual galaxies. Even eliminating these deviant galaxies, as well as those with poor quality profiles, the scatter of the luminosity - shape relation remains relatively high, despite that depth effects should not be important in this small group of galaxies. In addition, the fact that there is a lower limit in the size of galaxies which can be resolved in more distant clusters causes the observed luminosity - shape relation to change both its slope and its zero point as distance increases, limiting also its practical use as a distance indicator for groups of galaxies. An alternative is explored using the known relation between integrated magnitude and effective surface brightness as a distance indicator, and it is found that its zero point also changes depending on the mean sizes of the galaxies included in each sample. Mean distances for groups of galaxies obtained with this method should then be taken with care. The effects of seeing on the derived photometric parameters are also investigated in an empirical way. Three very faint, previously non-catalogued, dwarf-spheroidal galaxies were also detected, and their photometric data are given, along with their coordinates. ER - TY - Journal T1 - The Peculiar Morphology of the Irregular Galaxy NGC 1427A A1 - Cellone, Sergio A. A1 - Forte, Juan Carlos JO - Astronomical Journal VL - 113 Y1 - 1997/4/1 SP - 1239 EP - 1249 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997AJ....113.1239C&db_key=AST&high=42a068d47520762 N2 - Multicolor surface photometry and fragmentary low-resolution spectroscopy of the irregular galaxy NGC 1427A are presented. This galaxy, a member of the Fornax Cluster, has not been studied in detail previously. It shows a very distinctive morphology: a low surface brightness stellar background with several bright knots forming a distorted ring-like structure. A faint plume and several diffused filaments connect the northern part of the main body of the galaxy with an object having elliptical isophotes. The overall aspect of NGC 1427A, then, resembles that of known interacting galaxies. The very blue colors of the bright knots show that they are composed by young stars, and several of them also show emission lines. The northern object, which has itself a couple of these blue knots, is bluer than the background of the main body of the galaxy. This fact indicates that the star formation histories in both objects have been different. Morphologically, the northern object is similar to the numerous dwarf elliptical or irregular galaxies that populate the Fornax Cluster. The possibility of an interaction being the cause of the particular structure of this galaxy is discussed. ER - TY - Journal T1 - Washington Photometry of Low Surface Brightness Dwarf Galaxies in the Fornax Cluster: Constraints on Their Stellar Populations A1 - Cellone, Sergio A. A1 - Forte, Juan Carlos JO - Astrophysical Journal VL - 461 Y1 - 1996/4/1 SP - 176 KW - GALAXIES: PHOTOMETRY/ GALAXIES: STELLAR CONTENT UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...461..176C&db_key=AST&high=42a068d47520762 N2 - Integrated colors of a sample of low surface brightness (LSB) dwarf galaxies in the Fornax cluster, obtained from CCD images in the Washington system, are analyzed. This System proves useful to, under certain conditions, disentangle the effects of age and metallicity in a color-color diagram. A comparison with synthetic colors of simple stellar systems of known age and metallicity shows that nearly half the dwarfs have colors that can only be reproduced by a mixture of stars including a moderately young (~10^8^ yr) population. In particular, one of the galaxies shows evidence of recent or current star formation. ER - TY - Journal T1 - An Effelsberg HI study of the ISM around WR 126, WR 154 and WR 155 A1 - Cichowolski, S. A1 - Arnal, E. M. JO - Astronomy and Astrophysics VL - 414 Y1 - 2004/1/1 SP - 203 EP - 209 KW - ISM: bubbles/ stars: Wolf-Rayet/ stars: individual: WR 126/ WR 154/ WR 155 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...414..203C&db_key=AST&high=42a068d47524263 N2 - The neutral hydrogen distribution has been studied in the direction of three Galactic Wolf-Rayet (WR) stars using the 100 m Effelsberg radio telescope. Cavities in the HI distribution, regions of low HI emissivity, are observed over a 8-9 km s^-1, velocity range for WR 126 (â‰¡ST 2), WR 154 (â‰¡HD 213049) and WR 155 (â‰¡HD 214419). These minima are interpreted as the observable 21-cm HI line counterpart of interstellar bubbles created by the winds of the WR stars and their progenitors. The HI cavities are elongated structures depicting an axial ratio ranging from 1.3 (WR 155) to 3 (WR 126). The WR stars are always eccentric with respect to either the geometric centre of the HI cavity or the absolute minimum inside it. This offset ranges from 50% to 80% of the HI hole's minor axis. The major axis of these structures range from 13 (WR 155) to 27 pc (WR 126), while the missing HI mass amounts to 45-50 M_âŠ™ (WR 126), 60 M_âŠ™ (WR 155) and 85 M_âŠ™ (WR 154). Figures 1, 3, 5 are only available in electronic form at http://www.edpsciences.org ER - TY - Journal T1 - The interstellar medium local to HD 10125 A1 - Cichowolski, S. A1 - Arnal, E. M. A1 - Cappa, C. E. A1 - Pineault, S. A1 - St-Louis, N. JO - Monthly Notices of the Royal Astronomical Society VL - 343 Y1 - 2003/7/1 SP - 47 EP - 55 KW - stars: individual: HD 10125/ ISM: bubbles/ HII regions/ infrared: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.343...47C&db_key=AST&high=42a068d47524263 N2 - Based on an HI line and 408- and 1420-MHz radio continuum survey carried out at the Dominion Radio Astrophysical Observatory (DRAO), the environment of the O star HD 10125 has been studied. In addition, complementary radio continuum images, as well as infrared data of the same region have been analysed. An arc-like structure is found in all the radio continuum data. From the 21-cm line data, an HI minimum is found in the velocity range -27 to -32 km s^-1. Although HD 10125 is not at the centre of the HI cavity, its eccentric position is consistent with the observed stellar proper motion. The HI cavity and the continuum arc-like structure show an excellent morphological correlation. The radio continuum emission has a spectral index (S_nu~nu^alpha) alpha= 0.0 +/- 0.1, which establishes the thermal nature of the arc-like feature. The dust temperature obtained from the infrared data is higher in the area where the continuum emission is present. A distance of 3 kpc is derived for the star, the HI cavity and the radio continuum structure. We conclude that all the features we have found are physically related to each other. The O star has enough energetic photons to both ionize the surrounding gas and heat up the dust and, through its powerful wind, also sweep up the HI and HII gas. ER - TY - Journal T1 - A DRAO and VLA Investigation of the Environment of WR 130 A1 - Cichowolski, S. A1 - Pineault, S. A1 - Arnal, E. M. A1 - Testori, J. C. A1 - Goss, W. M. A1 - Cappa, C. E. JO - Astronomical Journal VL - 122 Y1 - 2001/10/1 SP - 1938 EP - 1953 KW - ISM: H II Regions/ Infrared Radiation/ ISM: Bubbles/ ISM: H I/ stars: individual (WR 130)/ Stars: Wolf-Rayet UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....122.1938C&db_key=AST&high=42a068d47524263 N2 - The environment of the Wolf-Rayet (WR) star WR 130 has been studied using the 21 cm H I line and radio continuum data at 408 and 1420 MHz obtained with the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope. In addition, the H110alpha recombination line and 21 cm H I line were observed using the Very Large Array in the DnC and D configurations. The Sharpless H II region, Sh 98 (size ~15'), and two OB stars are observed near the Wolf-Rayet star position. An extended ring-shaped structure (G68.1+1.1) of size ~20' is observed in the radio continuum and infrared data. Of four compact radio sources seen superposed on the ring, one is an H II region of size ~3' (G68.14+0.92), while the others are probably extragalactic. The spectral index (S_nu~nu^alpha) of G68.1+1.1 is alpha=0.0+/-0.1. The thermal nature of G68.1+1.1 is confirmed by an analysis of the correlation between the brightness temperature at 21 cm and the brightness at 60 mum, as observed with IRAS. The DRAO H I data show an H I bubble in the velocity range -12 to 1 km s^-1. The most striking characteristic of the H I cavity is the excellent correlation with the radio continuum ring. The WR star is not at the center of the ring, but in the dense border to the east. This eccentric position can be explained by a combination of a high spatial velocity for the star and projection effects. The possible contribution of the OB stars present in the area is also considered. From our H110alpha observations, together with other recombination lines observed in the area, we deduce a distance of 12 kpc for the compact H II region G68.14+0.92 and 5 kpc for G68.1+1.1. We conclude that G68.1+1.1 is the radio counterpart of the optical H II region Sh 98, while G68.14+0.92 is a chance superposition of a much more distant source. The ionized mass of the ring is estimated at ~3000 M_solar and the rms electron density at ~3 cm^-3, assuming a homogeneous distribution. A missing H I mass of 500 M_solar is obtained for the cavity and an excess H I mass of 1500 M_solar for the shell. ER - TY - Journal T1 - BCD spectrophotometry of stars with the B[e] phenomenon. I. Fundamental parameters A1 - Cidale, L. A1 - Zorec, J. A1 - Tringaniello, L. JO - Astronomy and Astrophysics VL - 368 Y1 - 2001/3/1 SP - 160 EP - 174 KW - STARS: EMISSION-LINE/ B[E]/ STARS: FUNDAMENTAL PARAMETERS/ STARS: EVOLUTION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...368..160C&db_key=AST&high=42a068d47527379 N2 - Low resolution spectra in the lambda lambda3500 -4600 Å wavelength range of 23 stars with the B[e] phenomenon are presented. Spectral classification of 15 program stars was performed using the BCD spectrophotometric system, based on the study of the Balmer discontinuity, which is independent of interstellar and circumstellar dust extinctions and of circumstellar gas emissions and/or absorptions. From calibrations of the (lambda₁ ,D) BCD parameters we determined the (T_eff,log g, M_bol) of the studied stars. For stars where this method could not be applied, we tried to estimate the temperature of the central star by using the Balmer and He i emission lines and/or their visible energy distribution. The colour temperature and the temperatures obtained from the study of Balmer and He i lines are consistent with each other. The new results are compared with those obtained previously by other authors and discussed for each star individually. For some stars, differences between the effective temperatures derived using the BCD classification system and those obtained elsewhere, based on photometric or spectroscopic analysis, imply spectral-type classification disagreements ranging from 2-3 up to 6 B sub-spectral types. The fundamental parameters of AS 119, CD-24°5721, Hen2-91, HD 316375 and BD-11°4747 were determined for the first time. A simple method was introduced to calculate total (interstellar+circumstellar) dust extinction towards the studied stars. For HD 53179, which is a double stellar system, and for HD 45677 and HD 50138, which are suspected to be binaries, we predicted the characteristics of the components that are consistent with the observed (lambda₁ ,D) parameters. However, the possible binarity of HD 45677 and HD 50138 still needs to be confirmed spectroscopically. Data obtained in CASLEO operated under agreement between the CONICET and the Universities of La Plata, Córdoba and San Juan, Argentina. Partially based on observations done at ESO La Silla, Chili. ER - TY - Journal T1 - Diagnosis of Stellar Winds and Temperature Structures in Be Stars through the Analysis of Mg II Lines A1 - Cidale, Lydia S. JO - Astrophysical Journal VL - 502 Y1 - 1998/8/1 SP - 824 KW - STARS: CIRCUMSTELLAR MATTER/ LINE: PROFILES/ RADIATIVE TRANSFER/ STARS: EMISSION-LINE/ BE/ STARS: MASS LOSS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...502..824C&db_key=AST&high=42a068d47527379 N2 - We compute non-LTE Mg II line profiles for Be stars by considering 12 energy-level atoms and supposing that the circumstellar medium can be described by an expanding, spherically symmetric flow in which we assume the presence of a chromosphere. The line radiative transfer equation was solved rigorously in spherical coordinates and in the comoving frame. The Mg II line profiles predicted by this model coincide with those observed in some Be stars. The calculation was performed for a range of effective temperatures representative of the B spectral type. We have also analyzed the influence on the line profiles of different temperature and velocity distributions in the circumstellar material. The line spectrum variability of a Be star is interpreted as the result of a variable outward mass flux. ER - TY - Journal T1 - Expanding Atmospheric Model Including a Chromosphere. II. Be Stars: Center-to-Limb Variation of the Emergent Intensity A1 - Cidale, Lydia S. A1 - Vazquez, Andrea C. JO - Astrophysical Journal VL - 453 Y1 - 1995/11/1 SP - 393 KW - RADIATIVE TRANSFER/ STARS: CHROMOSPHERES/ STARS: EMISSION-LINE/ BE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ApJ...453..393C&db_key=AST&high=42a068d47527379 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...453..393C&db_key=AST ER - TY - Journal T1 - Arnold diffusion: an overview through dynamical astronomy A1 - Cincotta, Pablo M. JO - New Astronomy Review VL - 46 Y1 - 2002/1/1 SP - 13 EP - 39 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002NewAR..46...13C&db_key=AST&high=42a068d47528483 N2 - The aim of this work is to review the fundamental ideas behind the stability problem, emphasizing the differences between two well-known mechanisms that could lead to chaos, namely overlap of resonances and Arnold diffusion. Here we restrict the discussion to multidimensional autonomous Hamiltonian systems which are of major relevance in Dynamical Astronomy. Arnold diffusion is reviewed in a standard mathematical language, by means of different tools such as heuristic reasoning, graphic and geometrical considerations and numerical experiments. In this direction the pioneer work due to Chirikov [PhR 52 (1979) 263] is followed, but including additional notes, further examples and useful discussions that may well illuminate the understanding of Arnold diffusion. We also summarize the main difficulties when coping with this instability, from both the analytical and numerical sides of the problem. The discussion whether Arnold diffusion could play any role in the dynamical evolution of, for instance elliptical galaxies, is also included. ER - TY - Journal T1 - Simple tools to study global dynamics in non-axisymmetric galactic potentials - I A1 - Cincotta, P. M. A1 - Simó, C. JO - Astronomy and Astrophysics Supplement Series VL - 147 Y1 - 2000/12/1 SP - 205 EP - 228 KW - GALAXIES: DYNAMICS/ STELLAR DYNAMICS/ METHODS: ANALYTICAL-NUMERICAL/ CHAOS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26AS..147..205C&db_key=AST&high=42a068d47528483 N2 - In a first part we discuss the well-known problem of the motion of a star in a general non-axisymmetric 2D galactic potential by means of a very simple but almost universal system: the pendulum model. It is shown that both loop and box families of orbits arise as a natural consequence of the dynamics of the pendulum. An approximate invariant of motion is derived. A critical value of the latter sharply separates the domains of loops and boxes and a very simple computation allows to get a clear picture of the distribution of orbits on a given energy surface. Besides, a geometrical representation of the global phase space using the natural surface of section for the problem, the 2D sphere, is presented. This provides a better visualization of the dynamics. In a second part we introduce a new indicator of the basic dynamics, the Mean Exponential Growth factor of Nearby Orbits (MEGNO), that is suitable to investigate the phase space structure associated to a general Hamiltonian. When applied to the 2D logarithmic potential it is shown to be effective to obtain a picture of the global dynamics and, also, to derive good estimates of the largest Lyapunov characteristic number in realistic physical times. Comparisons with other techniques reveal that the MEGNO provides more information about the dynamics in the phase space than other wide used tools. Finally, we discuss the structure of the phase space associated to the 2D logarithmic potential for several values of the semiaxis ratio and energy. We focus our attention on the stability analysis of the principal periodic orbits and on the chaotic component. We obtain critical energy values for which connections between the main stochastic zones take place. In any case, the whole chaotic domain appears to be always confined to narrow filaments, with a Lyapunov time about three characteristic periods. ER - TY - Journal T1 - Astronomical time-series analysis - III. The role of the observational errors in the minimum entropy method A1 - Cincotta, Pablo M. JO - Monthly Notices of the Royal Astronomical Society VL - 307 Y1 - 1999/8/1 SP - 941 EP - 948 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.307..941C&db_key=AST&high=42a068d47528483 N2 - In two recent papers a new method for searching for periodicity in time series was introduced. It takes advantage of the Shannon entropy to compute the amount of information contained in the light curve of a given signal as a function of a supposed period p. The basic result is that, if the signal is T-periodic, the entropy is then minimum when pT. Also, there is theoretical and numerical evidence that the minimum entropy method is more sensitive to the presence of periodicity and has a higher resolution power than other classical techniques. In the present work the discussion is focused on the way in which the observational errors have to be included in the method. The application of the resulting modified algorithm to real data and a performance comparison with the former algorithm are presented. The dependence of both periodograms on the size of the partition is also investigated. Analytical estimates are given only for the limiting case of small errors. The numerical results show that the new algorithm leads to a smoother periodogram and provides a higher significance for the minimum than the former algorithm. ER - TY - Journal T1 - Astronomical time-series analysis -- II. A search for periodicity using the Shannon entropy A1 - Cincotta, Pablo M. A1 - Helmi, Amina A1 - Mendez, Mariano A1 - Nunez, Josue A. A1 - Vucetich, Hector JO - Monthly Notices of the Royal Astronomical Society VL - 302 Y1 - 1999/1/1 SP - 582 EP - 586 KW - METHODS: ANALYTICAL/ METHODS: DATA ANALYSIS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.302..582C&db_key=AST&high=42a068d47528483 N2 - We have recently introduced a new method of searching a time series for periodic variability. The method uses the Shannon entropy to measure the amount of information provided by a set of observations that may contain an underlying periodic signal, as a function of the assumed period of this hypothetical periodic signal. Here we present the analytical arguments that support this algorithm within the broader frame of information theory. We also show that, in the absence of a periodic signal, the entropies follow a Gaussian distribution, which then provides an easy way of assessing the significance of a positive detection. We test this method using simulated data with non-sinusoidal variability, and we show that it is more sensitive than the classical periodograms or those variations adapted to deal with cases where harmonics are involved. Finally, we show that this method is capable of resolving two, almost identical, frequencies present in a given time series, even in cases where the classical periodograms fail to do so. ER - TY - Journal T1 - Conditional Entropy A1 - Cincotta, P. A1 - Simó, C. JO - Celestial Mechanics and Dynamical Astronomy VL - 73 Y1 - 1999/1/1 SP - 195 EP - 209 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999CeMDA..73..195C&db_key=AST&high=42a068d47528483 N2 - In this paper we show that the Conditional Entropy of nearby orbits may be a useful tool to explore the phase space associated to a given Hamiltonian. The arc length parameter along the orbits, instead of the time, is used as a random variable to compute the entropy. In the first part of this work we summarise the main analytical results to support this tool while, in the second part, we present numerical evidence that this technique is able to localise (stable) periodic and quasiperiodic orbits, 'aperiodic' orbits (chaotic motion) and unstable periodic orbits (the 'source' of chaotic motion). Besides, we show that this technique provides a measure of chaos which is similar to that given by the largest Lyapunov Characteristic Number. It is important to remark that this method is very simple to compute and does not require long time integrations, just realistic physical times. ER - TY - Journal T1 - On the Radial Orbit Instability A1 - Cincotta, Pablo M. A1 - Nunez, Josue A. A1 - Muzzio, Juan C. JO - Astrophysical Journal VL - 456 Y1 - 1996/1/1 SP - 274 KW - INSTABILITIES/ CELESTIAL MECHANICS/ STELLAR DYNAMICS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...456..274C&db_key=AST&high=42a068d47528483 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...456..274C&db_key=AST ER - TY - Journal T1 - Astronomical Time Series Analysis. I. A Search for Periodicity Using Information Entropy A1 - Cincotta, Pablo M. A1 - Mendez, Mariano A1 - Nunez, Josue A. JO - Astrophysical Journal VL - 449 Y1 - 1995/8/1 SP - 231 KW - METHODS: ANALYTICAL/ METHODS: NUMERICAL/ STARS: VARIABLES: OTHER UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ApJ...449..231C&db_key=AST&high=42a068d47528483 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..231C&db_key=AST ER - TY - Journal T1 - Library of flux-calibrated echelle spectra of southern late-type dwarfs with different activity levels A1 - Cincunegui, C. A1 - Mauas, P. J. D. JO - Astronomy and Astrophysics VL - 414 Y1 - 2004/2/1 SP - 699 EP - 706 KW - atlases/ stars: late-type UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...414..699C&db_key=AST&high=42a068d47530989 N2 - We present Echelle spectra of 91 late-type dwarfs, of spectral types from F to M and of different levels of chromospheric activity, obtained with the 2.15 m telescope of the CASLEO Observatory located in the Argentinean Andes. Our observations range from 3890 to 6690 Å, at a spectral resolution from 0.141 to 0.249 Å per pixel (R=lambda/delta lambda â‰ˆ 26 400). The observations were flux calibrated with the aid of long slit spectra. A version of the calibrated spectra is available via the World Wide Web. Table 2 is also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/699 The spectra are available as FITS and ascii-files at the URL: http://www.iafe.uba.ar/cincunegui/spectra/Table2.html. They are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/699. When converting the fits to ascii, the spectra were oversampled to a constant delta lambda â‰ˆ 0.15 Å. Table 2 is also available in electronic form at the CDS via anonymous ER - TY - Journal T1 - Blue Lines as Chromospheric Diagnostics: The Si I Lines at 3906 and 4103 Å A1 - Cincunegui, Carolina A1 - Mauas, Pablo J. D. JO - Astrophysical Journal VL - 552 Y1 - 2001/5/1 SP - 877 EP - 888 KW - Atomic Processes/ Line: Formation/ Line: Profiles/ Stars: Chromospheres/ Sun: Chromosphere UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...552..877C&db_key=AST&high=42a068d47530989 N2 - We present a complete atomic model for Si I line synthesis. We study how the computed profiles of two blue lines of this atom are influenced by the choice of the atomic parameters and find that, although several cross sections are not known accurately, the line profiles do not depend strongly on them and are therefore useful as diagnostics of the atmospheric structure. We study which transitions need not be included in the model, in order to reduce as much as possible the computing time. We compare the profiles computed for a standard model of the quiet solar atmosphere with the observations and find very good agreement. We confirm that irradiation by UV lines originating in the transition region above sunspot umbrae or plages strongly enhances the continuum between 1300 and 1700 Å, which is due to Si I bound-free transitions. If line fluxes typical of the impulsive phase of flares are assumed, the line profiles are also affected. ER - TY - Journal T1 - CCD BVI Photometry of the Southern Open Clusters Pismis 23 and BH 222 A1 - Clariá, Juan J. A1 - Piatti, Andrés E. JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 353 EP - 362 KW - open clusters-Pismis 23/ BH 222-photometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..353C&db_key=AST&high=42a068d47531282 N2 - CCD BVI Johnson Cousins photometry of the open cluster candidates Pismis 23 and BH 222 is presented. Both the analysis of the colour-magnitude diagrams and star counts performed in the regions of these two objects support their physical reality. For Pismis 23 we derive E(B-V) = 2.0 ± 0.1, E(V-I) = 2.6 ± 0.1, a distance from the Sun d= (2.6 ± 0.6) kpc and an age of (300 ± 100) Myr, while for BH 222 we obtain E(V-I) = 2. 4 ± 0.2, d= (6.0 ± 2.7) kpc and (60 ± 30) Myr. Both objects, located beyond the Sagittarius arm, are among the most reddened and distant open clusters known in the direction towards the Galactic centre. ER - TY - Journal T1 - IC 2395 and BH 47: Only one open cluster in the Vela constellation A1 - Clariá, J. J. A1 - Lapasset, E. A1 - Piatti, A. E. A1 - Ahumada, A. V. JO - Astronomy and Astrophysics VL - 409 Y1 - 2003/10/1 SP - 541 EP - 551 KW - methods: observational/ techniques: photometric/ stars: fundamental parameters/ open clusters and associations: individual: IC 2395/ BH 47 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...409..541C&db_key=AST&high=42a068d47531282 N2 - We report UBV photoelectric photometry for 273 stars in the fields of the open clusters IC 2395 and BH 47. Our postulate is that, rather than two different clusters in this region of Vela, there is only one, which we call IC 2395 = BH 47. The cluster is centered at about alpha = 8^{h} 42fm 5, delta = -48degr 06farcm 8 (2000), its angular diameter being ~ 19'. The analysis of the photometric data yields 61 probable cluster members and 16 possible members. Photometric membership probabilities show good agreement with those obtained from a proper motion study for 21 stars in common. The reddening across the cluster appears to be uniform, the mean E(B-V) value being 0.09 +/- 0.02. The true distance modulus is (V-M_V)₀ = 9.52 +/- 0.10, corresponding to a distance from the Sun of (800 +/- 40) pc and 48 pc below the Galactic plane. The cluster age, determined by fitting isochrones with core overshooting, turns out to be (6 +/- 2) Myr. There is a strong likelihood that IC 2395 = BH 47 is physically connected to the Vela OB1C association. ER - TY - Journal T1 - Multicolour photometry and Coravel observations of stars in the southern open cluster IC 2488 A1 - Clariá, J. J. A1 - Piatti, A. E. A1 - Lapasset, E. A1 - Mermilliod, J.-C. JO - Astronomy and Astrophysics VL - 399 Y1 - 2003/2/1 SP - 543 EP - 551 KW - methods: observational/ open clusters and associations: individual: IC2488/ star: abundances/ stars: Hertzsprung-Russell (HR) diagram and C-M diagrams UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...399..543C&db_key=AST&high=42a068d47531282 N2 - We present new UBV photoelectric observations of 119 stars in the field of the southern open cluster IC 2488, supplemented by DDO and Washington photometry and Coravel radial velocities for a sample of red giant candidates. Nearly 50% of the stars sampled - including three red giants and one blue straggler - are found to be probable cluster members. Photometric membership probabilities of the red giant candidates show good agreement with those obtained from Coravel data. A mean radial velocity of (-2.63 +/- 0.06) km s^-1 is derived for the cluster giants. The reddening across the cluster is found to be uniform, the mean value being E(B-V) = 0.24 +/- 0.04. IC 2488, located at a distance of (1250 +/- 120) pc from the Sun and 96 pc below the Galactic plane, is most probably not related to the planetary nebula ESO 166-PN21. A metal abundance [Fe/H] = 0.10 +/- 0.06 relative to the Sun is determined from DDO data of the red giant members, in good agreement with the [Fe/H] values derived from five independent Washington abundance indices. An age of 180 Myr is determined from the fitting of isochrones computed with convective overshooting for Z = 0.019. The isochrone for log t = 8.25 reproduces remarkably well not only the morphology of the upper main sequence but also the observed red giant pattern. Based on observations made at Las Campanas Observatory (Chile) and Cerro Tololo Inter-American Observatory (Chile), National Optical Astronomy Observatories, operated by the Association of the Universities for Research in Astronomy, Inc., under contract with the National Science Foundation and on observations collected with the Danish 1.54-m telescope at the European Southern Observatory, La Silla (Chile). Tables 1 and 4b are only available in electronic from at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/543 ER - TY - Journal T1 - Membership, binarity and metallicity of red giants in the southern open cluster NGC 2354 A1 - Clariá, J. J. A1 - Mermilliod, J.-C. A1 - Piatti, A. E. JO - Astronomy and Astrophysics Supplement Series VL - 134 Y1 - 1999/1/1 SP - 301 EP - 308 KW - OPEN CLUSTERS: INDIVIDUAL: NGC 2354/ STARS: HR DIAGRAM/ ABUNDANCES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26AS..134..301C&db_key=AST&high=42a068d47531282 N2 - We present new Coravel radial-velocity observations and photoelectric photometry in the UBV, DDO and Washington systems for a sample of red giant candidates in the field of the intermediate-age open cluster NGC 2354. Photometric membership probabilities show very good agreement with those obtained from Coravel radial velocities. The analysis of the photometric and kinematical data allow us to confirm cluster membership for 9 red giants, one of them being a spectroscopic binary, while 4 confirmed spectroscopic binaries appear to be probable members. We have also discovered 4 spectroscopic binaries not belonging to the cluster. A mean radial velocity of (33.40 +/- 0.27) km s(-1) and a mean reddening E(B-V) = 0.13 +/- 0.03 were derived for the cluster giants. NGC 2354 has a mean ultraviolet excess = -0.03 +/- 0.01, relative to the field K giants, and a mean new cyanogen anomaly Delta CN = -0.035 +/- 0.007, both implying [Fe/H] ~ -0.3. The moderately metal-poor character of NGC 2354 is confirmed using five different metal abundance indicators of the Washington system. The cluster giant branch is formed by a well defined clump of 7 stars and 4 stars with high membership probabilities seem to define an ascending giant branch. The whole red giant locus cannot be reproduced by any theoretical track. Based on observations collected with the Danish\protect\linebreak 1.54-m telescope at the European Southern Observatory, La Silla (Chile); at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan, Argentina, and at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. ER - TY - Journal T1 - Photometric study of the open cluster NGC2323 A1 - Claria, J. J. A1 - Piatti, A. E. A1 - Lapasset, E. JO - Astronomy and Astrophysics Supplement Series VL - 128 Y1 - 1998/2/1 SP - 131 EP - 138 KW - OPEN CLUSTERS: INDIVIDUAL: NGC2323/ OPEN CLUSTERS: GENERAL/ HR DIAGRAM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..128..131C&db_key=AST&high=42a068d47531282 N2 - UBV photoelectric photometry for 175 stars in the field of the southern open cluster NGC2323, supplemented by DDO photometry of 5 probable giants, is presented. The analysis of the photometric data yields 109 probable members; one of them being a red giant, and 3 possible members. The reddening across the cluster is slightly variable and the mean value E(B-V)=0.25. The apparent cluster distance modulus is 10.62, corresponding to a distance of 940 pc. The age, determined by fitting isochrones with core overshooting, turns out to be 100+/- 20 Myr. Other fundamental cluster parameters are also determined. NGC2323 appears not to be physically connected to the CMa OB1 association. Based on observations made at Cerro Tololo Inter-American Observatory (Chile) and at Las Campanas Observatory (Chile). ER - TY - Journal T1 - DDO Metal Abundances of High-Luminosity Late-Type Stars in Galactic Open Clusters A1 - Claria, Juan J. A1 - Piatti, Andres E. A1 - Osborn, Wayne JO - Publications of the Astronomical Society of the Pacific VL - 108 Y1 - 1996/8/1 SP - 672 KW - OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ STARS: LATE-TYPE/ STARS: ABUNDANCES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996PASP..108..672C&db_key=AST&high=42a068d47531282 N2 - Results from UBV and DDO photometry are presented for 54 high-luminosity late-type stars in the fields of 23 open clusters. The probability of cluster membership for each observed star is evaluated using two independent photometric criteria. It is found that 32 stars are very likely cluster members, the remaining ones being almost certainly field objects. The recently improved calibrations of the DDO system have been used to derive MK spectral types, effective temperatures, and metallicities, while E(B-V) color excesses have been determined through known photometric and spectroscopic procedures. The DDO metallicities range between values typical of moderately metal-poor ([Fe/H]=~ -0.3) to moderately metal-rich ([Fe/H] =~ 0.2) clusters. The masses of the cluster giants range between 1 and 4 solar masses, with the scatter within a cluster being less than 1 solar mass. (SECTION: Stellar Clusters and Associations) ER - TY - Journal T1 - The Type IC SN 1990B in NGC 4568 A1 - Clocchiatti, Alejandro A1 - Suntzeff, Nicholas B. A1 - Phillips, Mark M. A1 - Filippenko, Alexei V. A1 - Turatto, Massimo A1 - Benetti, Stefano A1 - Cappellaro, Enrico A1 - Avilés, Roberto A1 - Covarrubias, Ricardo A1 - DeGioia-Eastwood, K. A1 - Dickinson, Mark A1 - Gouiffes, Christian A1 - Guhathakurta, Puragra A1 - Hamuy, Mario A1 - Heathcote, Steve R. A1 - Leibundgut, Bruno A1 - Matheson, Thomas A1 - Navarrete, Mauricio A1 - Perez, M. A1 - Phillips, Andrew A1 - Piemonte, Antonello A1 - Ruiz, María T. A1 - Shields, Joseph C. A1 - Smith, Chris A1 - Spinrad, Hyron A1 - Sturch, Conrad R. A1 - Tyson, J. Anthony A1 - Wells, Lisa JO - Astrophysical Journal VL - 553 Y1 - 2001/6/1 SP - 886 EP - 896 KW - Stars: Supernovae: General/ Stars: Supernovae: Individual: Alphanumeric: SN 1990B UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...553..886C&db_key=AST&high=42a068d47500764 N2 - We present a study of the Type Ic supernova (SN) 1990B that includes most of the observations obtained from around the world. The combined data set comprises 84 BV(RI)_c photometric points spanning approximately 360 days after maximum light and 14 spectra from 5 up to ~150 days after maximum light. In contrast to other Type Ic SNe, SN 1990B did not display a weak but distinct He I lambda5876 line indicating that its He content was smaller or that the He layers were rather effectively shielded from the radioactive matter in the ejecta. The behavior of the Na I D line, however, suggests that He I lambda5876 was blended with it. SN 1990B appeared on a sharply varying background that complicates the usual techniques of digital photometry. In order to do unbiased photometry, we modeled and subtracted the background of each image with the SN using images of NGC 4568 taken ~2500 days after the explosion, when SN 1990B had faded beyond detection. We compare the performance of standard point-spread function fitting photometry of the SN in the images with and without the background of the parent galaxy and find the results to differ systematically at late times. The photometry done on the images with the background light of NGC 4568 subtracted shows the light curves of SN 1990B to be of the slow Type Ic variety, with a slope steeper than that of the Type Ib SN 1983N or the Type II transition (Type IIb) SN 1993J but slower than that of the Type Ic SN 1994I. We estimate the reddening by foreground matter in the Galaxy and NGC 4568 and compute BV(RI)_c light curves spanning ~110 days after maximum light. ER - TY - Journal T1 - The Luminous Type IC Supernova 1992AR at z=0.145 A1 - Clocchiatti, Alejandro A1 - Phillips, Mark M. A1 - Suntzeff, Nicholas B. A1 - DellaValle, Massimo A1 - Cappellaro, Enrico A1 - Turatto, Massimo A1 - Hamuy, Mario A1 - Avilés, Roberto A1 - Navarrete, Mauricio A1 - Smith, Chris A1 - Rubenstein, Eric P. A1 - Covarrubias, Ricardo A1 - Stetson, Peter B. A1 - Maza, José A1 - Riess, Adam G. A1 - Zanin, Caterina JO - Astrophysical Journal VL - 529 Y1 - 2000/2/1 SP - 661 EP - 674 KW - COSMOLOGY: OBSERVATIONS/ STARS: SUPERNOVAE: GENERAL/ SUPERNOVAE: INDIVIDUAL (SN 1992AR) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...529..661C&db_key=AST&high=42a068d47500764 N2 - We present spectroscopic and photometric observations of SN 1992ar, the most distant supernova (SN) in the Calán/Tololo Survey. We compare its spectrum with those of nearby Type Ia and Ic SNe and conclude that the latter type is a better match to SN 1992ar. Using K-corrections based on the spectra of well-observed Type Ic and Ia SNe, we compute different possible rest-frame light curves of SN 1992ar and compare them with those of representative SNe of each type observed in the nearby universe. From the photometry and the spectra, we are able to conclude that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even though the data set collected is fairly complete (one spectrum and 10 photometric points), it is not possible to decide whether SN 1992ar was a fast Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V magnitudes at maximum implied by each of these possibilities are -19.2 and -20.2, respectively. The latter would make SN 1992ar one of the brightest SNe on record. SN 1992ar, hence, illustrates the problem of contamination faced by the high-z Type Ia SNe samples whose luminosity distances are used to determine the cosmological parameters of the universe. We present observational criteria to distinguish the two SN types when the Si II 6355 Å line is redshifted out of the sensitivity range of typical CCD detectors and discuss the effect that these luminous Type Ic SNe would have on the measured cosmological parameters, if not removed from the high-z Type Ia SN samples. ER - TY - Journal T1 - On the Light Curves of Stripped-Envelope Supernovae A1 - Clocchiatti, A. A1 - Wheeler, J. C. JO - Astrophysical Journal VL - 491 Y1 - 1997/12/1 SP - 375 KW - STARS: SUPERNOVAE: GENERAL/ STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1983N/ STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1983V/ STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1993J/ STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1994I UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...491..375C&db_key=AST&high=42a068d47500764 N2 - Representative light curves of supernovae of Types Ib and Ic, and the peculiar Type II that makes a transition to Ib, are collected and analyzed. Their main characteristics are (1) a group of fast and heterogeneous light curves corresponding to spectroscopic Type Ic and (2) a group of intermediate and homogeneous light curves among which are examples of spectroscopic Types Ib, Ic, and II transition. The latter have a well-defined slope of ~0.019 mag day-1 after ~150 days. A simple model based on the deposition of the energy provided by the radioactive decay of 56Ni and 56Co in expanding spherical shells is presented and used to qualitatively explain these families of light curves. The gamma -ray deposition function has two different regimes. At early times, it is strongly dependent on the physical parameters of the shells, which explains the heterogeneity of group 1 above. At late times, however, it reaches an asymptotic regime in which the slope in excess of the 56Co decay rate is given by 5t-1 log e mag day-1, where t is the time since explosion in days, independently of any parameter of the ejecta. The photometric group 2 above may be, at least partially, a result of this asymptotic behavior. ER - TY - Journal T1 - SN 1983V in NGC 1365 and the Nature of Stripped Envelope Core-Collapse Supernovae A1 - Clocchiatti, A. A1 - Wheeler, J. C. A1 - Phillips, M. M. A1 - Suntzeff, N. B. A1 - Cristiani, S. A1 - Phillips, A. A1 - Harkness, R. P. A1 - Dopita, M. A. A1 - Beuermann, K. A1 - Rosa, M. A1 - Grosbol, P. A1 - Lindblad, P. O. A1 - Filippenko, A. V. JO - Astrophysical Journal VL - 483 Y1 - 1997/7/1 SP - 675 KW - GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1365/ STARS: EVOLUTION/ STARS: INTERIORS/ STARS: SUPERNOVAE: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...483..675C&db_key=AST&high=42a068d47500764 N2 - We present CCD photometry and low-resolution spectra of the spectroscopic Type Ic supernova SN 1983V in NGC 1365. Photometry in the B band spans nearly 250 days after maximum light, while the spectra cover the photospheric epoch, from 9 days before up to 38 days after B maximum. We also compile and discuss infrared photometry that has been published elsewhere. The photometric evolution of SN 1983V is analyzed in comparison with other Type Ic supernovae and with SN 1983N and SN 1993J. The spectroscopic evolution is described, line identifications are proposed, and evidence for H, He, and Si is discussed. The photometric evolution of SN 1983V suggests that it is a close relative of SN 1983N and SN 1993J, events for which it is supposed that the external layers comprising most of the He/H and H shells, respectively, were lost before the explosion. The mass-to-energy ratios of SN 1983V and SN 1993J are substantially different if estimated from the expansion velocities. However, the similarity of the B light curves suggests that if the masses and mass-to-energy ratios are not similar, then the mass of SN 1983V has to be large enough to compensate for the higher mass-to-energy ratio. The latter possibility contradicts the standard scenarios that describe these events and implies a precise fine-tuning of the masses and mass-to-energy ratios of the two supernovae. This contradiction, however, could be resolved if a significant fraction of the inner ejecta containing 56Ni does not follow the decrease in density expected for a spherically symmetric, homologous expansion. ER - TY - Journal T1 - SN 1994I: Disentangling He i Lines in Type IC Supernovae A1 - Clocchiatti, Alejandro A1 - Wheeler, J. Craig A1 - Brotherton, Michael S. A1 - Cochran, Anita L. A1 - Wills, Derek A1 - Barker, Edwin S. A1 - Turatto, Massimo JO - Astrophysical Journal VL - 462 Y1 - 1996/5/1 SP - 462 KW - STARS: ABUNDANCES/ STARS: SUPERNOVAE: GENERAL/ STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1994I UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...462..462C&db_key=AST&high=42a068d47500764 N2 - We present spectroscopic observations of the Type Ic supernova SN 1994I and analyze the evidence for helium in the optical portion of the spectrum. The development of high-velocity He I lambda5876 starting approximately 1 week after maximum light provides a pattern of evolution that can be used to discriminate He I lines in other Type Ic supernovae. We show that, contrary to earlier interpretation, SN 1987M displayed He I lines. The He abundance is, however, probably consistent with previously derived upper limits. We also identify He in SN 1988L. We conclude that most, and probably all, Type Ic supernovae show evidence for He I lines in the optical region of the spectra, which implies small amounts of high-velocity helium in the outer portions of the ejecta. The implications of this result for the progenitor stars are discussed. ER - TY - Journal T1 - SN 1983N and the Nature of Stripped Envelope--Core Collapse Supernovae A1 - Clocchiatti, A. A1 - Wheeler, J. C. A1 - Benetti, S. A1 - Frueh, M. JO - Astrophysical Journal VL - 459 Y1 - 1996/3/1 SP - 547 KW - GALAXIES: INDIVIDUAL MESSIER NUMBER: M83/ STARS: SUPERNOVAE: GENERAL/ STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1983N UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...459..547C&db_key=AST&high=42a068d47500764 N2 - We present CCD photometric observations of SN 1983N obtained from images taken 290 and 340 days after maximum light. These points define a late time slope of 0.017 + 0.003 mag day ^{1 }in the V band, nearly indistinguishable from that of SN 1993J at the same phase after second maximum. A comparative analysis of these two SNe shows that, although some puzzling differences exist, except for the outermost layers containing H in SN 1993J they were essentially similar, with the mass-to-energy ratio of SN 1993J probably larger. The similarity of the light curves of SN 1983N and SN 1993J has implications for the categorization of both Type Ib and Type II to Ib "transition" SNe. These two objects, together with SNe 1954A, 1987K, and 1983V, among others, seem to define a photometric group that cuts across the spectroscopic categories traditionally used to classify supernovae. The spectrum at maximum is insufficient to fully classify them. ER - TY - Journal T1 - A Study of SN 1992H in NGC 5377 A1 - Clocchiatti, Alejandro A1 - Benetti, Stefano A1 - Wheeler, J. Craig A1 - Wren, William A1 - Boisseau, J. A1 - Cappellaro, Enrico A1 - Turatto, Massimo A1 - Patat, Ferdinando A1 - Swartz, Douglas A. A1 - Harkness, Robert P. A1 - Brotherton, Michael S. A1 - Wills, Beverly A1 - Hemenway, Paul A1 - Cornell, Mark A1 - Frueh, Marian A1 - Kaiser, Mary B. JO - Astronomical Journal VL - 111 Y1 - 1996/3/1 SP - 1286 KW - SUPERNOVAE: INDIVIDUAL: SN 1992H/ GALAXIES: INDIVIDUAL: NGC 5377 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996AJ....111.1286C&db_key=AST&high=42a068d47500764 N2 - A photometric and Spectroscopic analysis is presented of SN 1992H in NGC 5377 which was discovered by W. Wren at McDonald Observatory on UT 1992 February 11.5. SN 1992H displayed a distinct but truncated plateau suggesting that it was in some sense intermediate between a type II- linear and a fully developed type II-plateau event. Explosion is estimated to have occurred about 3 days before discovery. BV(RI)c light curves plus bolometric corrections based on the behavior of SN 1987A are used to compute a UVOIR bolometric light curve. This light curve shows a broad decline from early epochs that merges smoothly into the "plateau" at about 50 days after explosion. About 85 days after the explosion the light curve begins a precipitate decline of about 2 mag in 45 days. At that point, 130 days after the explosion, the light curve begins a linear decline with the timescale appropriate to that of ^56^CO that lasts to the end of the observation at about 450 days. The early spectra show a continuum with Halpha in emission and Hbeta and He I lambda5876 with broad P Cygni profiles. Velocities at this phase are in excess of 10000 km s^-1^. By 50 days after the explosion, Halpha shows a well- developed P Cygni profile. Lines of Ca H & K, FeII, Sc II lambda5526 and 5658, Na D, [CaII] lambdalambda7291,7324, and the CaII IR triplet are also observed on the plateau. On the tail, lines of [O I] lambda5577 and [O I] lambdalambda6300,6364, and blends of [Fe II] are also observed. The latest spectra at about 450 days show a blue continuum. The B - V color evolution, the equivalent width of interstellar Na D, and the epoch of disappearance of He I lambda5876 are used to estimate a color excess of E(B - V) = 0.09 +/- 0.06. For this extinction, the expanding photosphere method is used to estimate a distance of 20.2+/-3.0 Mpc (mu} = 31.53+/-0.74). Models of the light curve show that the total mass ejected is about 11 M_sun_ with 0.075 M_sun_ of ^56^Ni. The latter is necessary to match both the distance- dependent amplitude of the exponential decline, but also the contrast between the plateau and the tail, which is independent of distance. The envelope of the progenitor must have extended to about 1000 R_sun_ with a density profile that dropped more slowly than exponential in order to match the relatively slow decline from the initial peak to the plateau. The decline from the plateau to the exponential tail was too precipitate in models with a distinct core-envelope discontinuity. It is unclear whether the smoother density contrast required is a constraint on the progenitor structure or may be induced by mixing in the explosion. Synthetic spectra in the late photospheric phase (50 and 119 days) are used to identify lines and estimate abundances. The results are consistent with solar abundances in the outer envelope. The evolution of the Halpha line strength is consistent with an ejecta mass of 10-14 M_sun_, as derived from the light curve calculation. This is somewhat less that the lower limit to the ejecta mass derived by the constraint that sufficient gamma ray opacity be required to maintain the light curve near the ^56^CO decay line for 450 days, which is > 15 M_sun_. The evolution of the [CaII] doublet and Ca II IR triplet were used to estimate the electron temperature and density and the mass of calcium. The electron temperature of the matter within 2500 km s^-1^ is found to be ~5500 K, the electron density to be 2.5 x 10^9^ cm^-3^. The mass of Ca is estimated to be 3.5 x 10^-4^ M_sun_. If this matter has solar abundances, the total mass of hydrogen containing this Ca would be 4.4 M_sun_. ER - Resorting Query Results for 2005AJ....129.1237C

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1	Â 2005AJ....129.1237C	1.000	03/2005	AÂ Â Â Â Â Â EÂ Â FÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â RÂ Â Â Â Â Â Â Â Â Â SÂ Â NÂ Â Â Â Â Â Â Â Â Â UÂ Â Â Â Â Â
	Coenda,Â Valeria; Donzelli,Â CarlosÂ JosÃ©; Muriel,Â Hernan; Quintana,Â Hernan; Infante,Â Leopoldo; Lambas,Â DiegoÂ GarcÃa	Photometric Observations of Southern Abell Clusters Redshifts Survey Clusters: Galaxy Luminosity Profiles

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Smithsonian/NASA ADS Homepage | ADS Sitemap | Query Form | Preferences | HELP | FAQ TY - Journal T1 - Star formation in quasar and active galaxy environments A1 - Coldwell, Georgina V. A1 - Lambas, Diego G. JO - Monthly Notices of the Royal Astronomical Society VL - 344 Y1 - 2003/9/1 SP - 156 EP - 160 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.344..156C&db_key=AST&high=42a068d47500639 N2 - We use the 2dF public 100 K data release of galaxies and samples of quasars and active galaxies taken from the Véron-Cetty and Véron catalogue to study the nature of galaxies in the surroundings of active objects with redshifts in the range 0.1 < z < 0.2. We explore the distribution of neighbour 2dF galaxy spectral types, eta, at different projected distances from the quasars and active galaxies with radial velocity difference DeltaV= 500 km s^-1. For comparison, we perform a similar analysis on the environment of typical galaxies in the 2dF catalogue, a sample of bright early-type galaxies, i.e. eta < -1.4 and M_{b_J} < -21, and also on a sample of 2dF galaxy groups. We find a higher relative fraction of emission-line galaxies, i.e. with 2dF spectral type indices eta >3.5, in the vicinity of quasars and active galaxies compared to that in the neighbourhood of typical galaxies, bright early types and groups. This effect extends up to projected distance r_p~ 1 h^-1 Mpc for active galaxies and r_p~ 3 h^-1 Mpc for quasars. We also find a tendency for companion galaxies of quasars to be brighter than the neighbours of active galaxies within r_p~ 3 h^-1 Mpc. We estimate average star-formation rates for objects at different distances from quasars, active galaxies, galaxies and groups. We find a significantly higher star-formation activity within ~2.0 h^-1 Mpc from quasars with respect to typical galaxies, which reinforces the idea that star formation is enhanced in the neighbourhood of quasars. Our tests with the group environment provide evidence against quasars being associated with groups. Also, our analysis of the neighbours of bright early types shows that although these galaxies are typical hosts of quasars, their companion galaxies are significantly different in terms of the star-formation activity. ER - TY - Journal T1 - The environment of active objects in the nearby Universe A1 - Coldwell, Georgina V. A1 - Martínez, Héctor J. A1 - Lambas, Diego G. JO - Monthly Notices of the Royal Astronomical Society VL - 336 Y1 - 2002/10/1 SP - 207 EP - 210 KW - galaxies: active/ galaxies: clusters: general/ quasars: general/ large-scale structure of Universe UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.336..207C&db_key=AST&high=42a068d47500639 N2 - We study the galaxy environment of active galaxies, radio-loud and radio-quiet quasars in the redshift range 0.1 <=z<= 0.25. We use galaxies from the APM survey in order to explore the local galaxy overdensity and the b_J-R colour distribution of neighbouring galaxies of these target samples. For comparison, we perform similar analysis on samples of Abell clusters with X-ray emission, and samples of Abell clusters with richness R= 1 and 0. The projected cross-correlations show that the samples of quasars and active galaxies reside in regions of galaxy density enhancements lower than those typical of R= 0 clusters. We also find that in the nearby Universe the local galaxy overdensities of radio-loud and radio-quiet quasars are comparable. The analysis of the distribution of b_J-R galaxy colour indices suggests that the environment of quasars is not strongly dominated by a population of red galaxies, characteristic of rich Abell clusters, an effect that is more clearly appreciated for our sample of radio-loud quasars. ER - TY - Journal T1 - SAC-C mission, an example of international cooperation A1 - Colomb, F. R. A1 - Alonso, C. A1 - Hofmann, C. A1 - Nollmann, I. JO - Advances in Space Research VL - 34 Y1 - 2004/1/1 SP - 2194 EP - 2199 KW - Sac-C mission/ International scientific cooperation UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..34.2194C&db_key=AST&high=42a068d47502265 N2 - The SAC-C is an international Earth observing satellite mission developed as a partnership between CONAE and NASA, with additional support in instrumentation and satellite development from the Danish DSRI, the Italian ASI, the French CNES and the Brazilian INPE. The SAC-C satellite was successfully launched by a Delta II rocket on November 21, 2000, from Vandenberg AFB, California, USA. The purpose of this mission is to carry out observations which bear interest both for the USA and Argentina, thus contributing effectively to NASA's Earth Science Program and to CONAE's National Space Program. The inclusion of SAC-C in the ``morning constellation'', jointly with NASA satellites Landsat 7, EO 1 and Terra, is another example of an important international cooperation which strengthens the output of any single mission. ER - TY - Journal T1 - Optical polarimetric observations of the microquasar LS 5039 A1 - Combi, J. A. A1 - Cellone, S. A. A1 - Martí, J. A1 - Ribó, M. A1 - Mirabel, I. F. A1 - Casares, J. JO - Astronomy and Astrophysics VL - 427 Y1 - 2004/12/1 SP - 959 EP - 963 KW - stars: individual: LS 5039/ X-rays: binaries/ stars: binaries: general/ polarization UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...427..959C&db_key=AST&high=42a068d47502084 N2 - We present the first optical polarimetric observations of the runaway microquasar LS 5039. Our results reveal the presence of a large amount (~5%) of polarized emission towards this binary system. By combining polarimetric and spectroscopic observations of some stars in the field together with available statistical information on the galactic interstellar polarization of the region, we have estimated and subtracted the contribution of the interstellar polarization in this direction. As a result, we obtain an intrinsic polarization of ~3% for the object, much higher than what would be expected from jet emission in the optical domain. We suggest that the polarized light originates by electron Thomson scattering in the stellar envelope of the companion star. This allows us to constrain the size of the region where the polarized emission originates, as well as estimating the scattering electronic density and the wind velocity at such distance. Based on observations made at the Complejo Astronómico El Leoncito, which is operated under agreement between CONICET and the National Universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - The dust-enshrouded microquasar candidate AX J1639.0-4642 = IGR J16393-4643 A1 - Combi, J. A. A1 - Ribó, M. A1 - Mirabel, I. F. A1 - Sugizaki, M. JO - Astronomy and Astrophysics VL - 422 Y1 - 2004/8/1 SP - 1031 EP - 1037 KW - stars: general/ stars: binaries: general/ radio continuum: stars/ gamma rays: observations/ infrared: stars UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...422.1031C&db_key=AST&high=42a068d47502084 N2 - We present a multiwavelength study of the field containing the unidentified X-ray source AX J1639.0-4642, discovered with the ASCA observatory and recently detected with the IBIS telescope, onboard the INTEGRAL satellite, dubbed IGR J16393-4643. The huge hydrogen column density towards the source, the hard spectral index in the 0.7-10 keV band and its flux variability suggest that the source is a High Mass X-ray Binary (HMXB) enshrouded by dust. Our search reveals the presence of a non-thermal radio counterpart within the X-ray error box. After a study of the broadband emission from X-rays to the radio domain, we propose that AX J1639.0-4642 is a dust-enshrouded Microquasar (MQ) candidate. In addition, the X-ray source is well within the 95% location contour of the unidentified gamma-ray source 3EG J1639-4702. The main properties of AX J1639.0-4642/3EG J1639-4702 are consistent with those of two other MQs previously proposed to display high-energy gamma-ray emission. ER - TY - Journal T1 - Discovery of a New Radio Galaxy within the Error Box of the Unidentified Gamma-Ray Source 3EG J1735-1500 A1 - Combi, J. A. A1 - Romero, G. E. A1 - Paredes, J. M. A1 - Torres, D. F. A1 - Ribó, M. JO - Astrophysical Journal VL - 588 Y1 - 2003/5/1 SP - 731 EP - 735 KW - Galaxies: Active/ Galaxies: Jets/ Gamma Rays: Observations/ Radio Continuum: Galaxies UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...588..731C&db_key=AST&high=42a068d47502084 N2 - We report the discovery of a new radio galaxy within the location error box of the gamma-ray source 3EG J1735-1500. The galaxy is a double-sided jet source forming a large angle with the line of sight. Optical observations reveal a V~18 mag galaxy at the position of the radio core. Although the association with the EGRET source is not confirmed at present because there is a competing, alternative gamma-ray candidate within the location error contours, which we also study here, the case deserves further attention. The new radio galaxy can be used to test the recently proposed possibility of gamma-ray-emitting radio galaxies beyond the already known case of Centaurus A. ER - TY - Journal T1 - The radio surroundings of the microquasar GRO J1655-40 A1 - Combi, J. A. A1 - Romero, G. E. A1 - Benaglia, P. A1 - Mirabel, I. F. JO - Astronomy and Astrophysics VL - 370 Y1 - 2001/4/1 SP - L5 EP - L8 KW - X-RAYS: STARS/ STARS: EVOLUTION/ ISM: BUBBLES/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...370L...5C&db_key=AST&high=42a068d47502084 N2 - We report the results of a study of the radio surroundings of the superluminal microquasar GRO J1655-40. We have searched for extended continuum structures that might be indicative of the presence of a supernova remnant (SNR) associated with the formation of the compact object in the binary system. We also carried out HI-line observations of the region looking for a local minimum created by an explosive event. Our results indicate that there is, in fact, a bubble in the large-scale HI distribution around GRO J1655-40. We suggest that this structure might be created by the original supernova explosion occurred a few hundred thousand years ago and whose signatures can be traced by the overabundance of alpha -elements recently found by Israelian et al. (\cite{Israelian99}) in the companion star. ER - TY - Journal T1 - Detection of a new, low-brightness supernova remnant possibly associated with EGRET sources A1 - Combi, J. A. A1 - Romero, G. E. A1 - Benaglia, P. A1 - Jonas, J. L. JO - Astronomy and Astrophysics VL - 366 Y1 - 2001/2/1 SP - 1047 EP - 1052 KW - ISM: SUPERNOVA REMNANTS/ RADIO CONTINUUM: ISM/ RADIATION MECHANISMS: NONTHERMAL/ GAMMA RAYS: OBSERVATIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...366.1047C&db_key=AST&high=42a068d47502084 N2 - We report on the discovery of a shell-type supernova remnant in the southern sky. It is a large ( ~ 8^deg x 8^deg), low-brightness source with a nonthermal radio spectrum, which requires background filtering to isolate it from the diffuse background emission of the Galaxy. Three 3EG gamma -ray sources are spatially correlated with the radio structure. We have made 21-cm line observations of the region and found that two of these sources are coincident with HI clouds. We propose that the gamma -ray emission is the result of hadronic interactions between high-energy protons locally accelerated at the remnant shock front and atomic nuclei in the ambient clouds. ER - TY - Journal T1 - A Search for Radio Counterparts of Southern Unidentified EGRET Sources A1 - Combi, J. A. A1 - Romero, G. E. A1 - Benaglia, P. JO - Astronomical Journal VL - 118 Y1 - 1999/8/1 SP - 659 EP - 665 KW - GAMMA RAYS/ RADIO CONTINUUM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....118..659C&db_key=AST&high=42a068d47502084 N2 - We present results of 1.42 GHz continuum and H I line observations of the environs of the unidentified EGRET sources 3EG J0724-4713 and 3EG J0725-5140. Using a filtering technique, we have eliminated from the radio continuum images the background diffuse radiation that originates in the Galactic disk. This enables us to study the presence of weak radio sources within the likelihood contours of the gamma-ray detections. The H I line observations provide additional information about the structure of the interstellar medium in the line of sight to the sources, which is relevant in case of a Galactic origin. We discuss the nature of the individual sources in the light of the results. ER - TY - Journal T1 - Radio Detection of the Supernova Remnant RX J0852.0-4622 A1 - Combi, J. A. A1 - Romero, G. E. A1 - Benaglia, P. JO - Astrophysical Journal VL - 519 Y1 - 1999/7/1 SP - L177 EP - L180 KW - ISM: COSMIC RAYS/ RADIATION MECHANISMS: NONTHERMAL/ RADIO CONTINUUM: GENERAL/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...519L.177C&db_key=AST&high=42a068d47502084 N2 - The X-ray source RX J0852.0-4622 has been recently proposed as a candidate for a young nearby supernova remnant on the basis of its X-ray (>=1.3 keV) morphology, inferred internal shock velocities, and the clear detection of ^44Ti emission lines. In this Letter, we report its detection at radio wavelengths (2.4 and 1.42 GHz). The radio images match the X-ray morphology very well and show a limb-brightened source with some elongated features protruding from the outer shell. These features could be explosion fragments similar to those detected in the Vela supernova remnant. At radio frequencies the source appears to be nonthermal, with an index ~-0.3. This synchrotron emission seems to extend up to X-ray energies, implying the existence of very high energy electrons locally accelerated in the remnant. ER - TY - Journal T1 - The gamma -ray source 2EGS J1703-6302: a new supernova remnant in interaction with an HI cloud? A1 - Combi, J. A. A1 - Romero, G. E. A1 - Benaglia, P. JO - Astronomy and Astrophysics VL - 333 Y1 - 1998/5/1 SP - L91 EP - L94 KW - GAMMA RAYS: OBSERVATIONS/ COSMIC RAYS/ RADIO CONTINUUM: ISM/ ISM: CLOUDS/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26A...333L..91C&db_key=AST&high=42a068d47502084 N2 - We present observational evidence supporting a picture where the gamma -ray source 2EGS J1703-6302 is the result of the interaction between cosmic rays (CRs) accelerated in a supernova remnant (SNR) and a nearby HI cloud. The SNR has been disclosed by filtering the diffuse disk emission from new 1.42 GHz continuum observations of the radio field around 2EGS J1703-6302. The cloud was detected through neutral hydrogen line observations of the same area of the sky. The CR enhancement in the SNR with respect to the local value is about a factor ~ 44. ER - TY - Journal T1 - The spur-like radio feature in Centaurus A1 - Combi, J. A. A1 - Romero, G. E. A1 - Arnal, E. M. JO - Astronomy and Astrophysics VL - 333 Y1 - 1998/5/1 SP - 298 EP - 304 KW - RADIO CONTINUUM: ISM/ ISM: STRUCTURE/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26A...333..298C&db_key=AST&high=42a068d47502084 N2 - We present a study of the radio emission of the Centaurus region at galactic latitudes 2(deg) <= b <= 18(deg) , using pre-existing 408MHz continuum data and results of new 1.42GHz continuum and neutral hydrogen line observations. It is shown that the extensive spur-like radio feature visible in this region has a non-thermal nature and is actually formed by several previously unidentified individual sources. Five new supernova remnant (SNR) candidates have been detected at relatively high latitudes. Three of them, as well as two former candidates reported by Duncan et al. (1995), were confirmed through the computation of their spectral indices. One of the new SNRs, G315.4+12.9, might be associated with the open cluster NGC 5460. ER - TY - Journal T1 - Observations of the radio emission field around the gamma -ray source 2EG J1834-2138 A1 - Combi, J. A. A1 - Romero, G. E. JO - Astronomy and Astrophysics Supplement Series VL - 128 Y1 - 1998/3/1 SP - 423 EP - 428 KW - GAMMA RAYS: OBSERVATIONS/ RADIO CONTINUUM: GALAXIES/ GALAXIES: ACTIVE/ GALAXIES: QUASARS: PKS 1830-211 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..128..423C&db_key=AST&high=42a068d47502084 N2 - We present results of a study of the radio emission field around the best estimate position of the low-latitude EGRET source 2EG J1834-2138. The identification of this gamma -ray source with the gravitational lensed AGN PKS 1830-211 has been recently proposed by \cite[Mattox et al. (1997)]{ma97}. Additional support for this identification is provided here. Contamination produced by the diffuse disk emission has been removed from new radio images of the surrounding region of 2EG J1834-2138 allowing a determination of the fine radio structure. Several previously unnoticed supernova remnants have been found within a few degrees from the gamma -ray source. However, the only strong radio source within the 95% source location confidence contour of 2EG J1834-2138 is PKS 1830-211. In addition, both spectrum and variability analysis of the EGRET data support the identification of both sources. ER - TY - Journal T1 - The large-scale radio spectral index distribution of Centaurus A A1 - Combi, J. A. A1 - Romero, G. E. JO - Astronomy and Astrophysics Supplement Series VL - 121 Y1 - 1997/1/1 SP - 11 EP - 14 KW - GALAXIES: INDIVIDUAL: NGC 5128=CEN A/ GALAXIES: ACTIVE/ RADIO UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26AS..121...11C&db_key=AST&high=42a068d47502084 N2 - A spectral index map of Centaurus A (Cen A) has been computed using 408 MHz observations from the whole-sky survey by \cite[Haslam et al. (1981)]{ref10} and new 1435 MHz observations. The large-scale structure of the radio source is discussed in the light of these new data and a previous polarization survey. The observational evidence seems to support the expanding jet model for this source. ER - TY - Journal T1 - A Non-Thermal Radio Source Detected Towards PSR 1055-52 A1 - Combi, J. A. A1 - Romero, G. E. A1 - Azcarate, I. N. JO - Astrophysics and Space Science VL - 250 Y1 - 1997/1/1 SP - 1 EP - 9 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997Ap%26SS.250....1C&db_key=AST&high=42a068d47502084 N2 - We report the detection of a weak and extended source in the radio continuum at 1.42 GHz around the position of the high energy gamma ray pulsar PSR 1055-52. The source is also detectable at 408 MHz. It presents non-thermal spectral indices suggesting a synchrotron nature. We discuss the possibility of a physical association with the pulsar. ER - TY - Journal T1 - On the origin of the gamma-ray fields in the ARA region. A1 - Combi, J. A. A1 - Romero, G. E. JO - Astronomy and Astrophysics VL - 303 Y1 - 1995/11/1 SP - 872 KW - ISM: SUPERNOVA REMNANTS/ CLOUDS/ RADIO CONTINUUM: ISM/ GAMMA RAYS: OBSERVATIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...303..872C&db_key=AST&high=42a068d47502084 N2 - We report and discuss results of 1435MHz observations of the continuum emission from the Ara region. Using data from the previous 408MHz all-sky survey by Haslam et al. (1981) we have computed the spectral index distribution in the region. After the subtraction of a background component, several interesting features can be observed at both frequencies. We pay particular attention to an extended nonthermal source which is coincident with a strong gamma-ray emission zone at 10deg from the galactic plane. We suggest that this feature could be the result of the interaction of a supernova remnant (SNR) with an interstellar cloud. Our interpretation can explain both the nonthermal nature of the radio source as well as the enhancement in the gamma-ray flux. Several parameters are estimated for this context and other possible interpretations are briefly discussed. ER - TY - Journal T1 - 1435MHz continuum observations of Upper-Scorpius. A1 - Combi, J. A. A1 - Testori, J. C. A1 - Romero, G. E. A1 - Colomb, F. R. JO - Astronomy and Astrophysics VL - 296 Y1 - 1995/4/1 SP - 514 KW - ISM: STRUCTURE/ SUPERNOVA REMNANTS/ SHOCK WAVES/ RADIO CONTINUUM: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...296..514C&db_key=AST&high=42a068d47502084 N2 - We report total-power observations at 1435MHz of the Upper-Scorpius region. The spectral index distribution has been computed using available data from a previous 408MHz all-sky survey by Haslam et al. (1981). An extended spur-like structure dominated by nonthermal emission has been detected surrounding the region. We discuss the origin and nature of this region on the basis of a model of the interaction between a shock front and a cloudy ISM. Several physical parameters are estimated. ER - TY - Journal T1 - Building blocks in hierarchical clustering scenarios and their connection with damped Lyalpha systems A1 - Cora, Sofía A. A1 - Tissera, Patricia B. A1 - Lambas, Diego G. A1 - Mosconi, Mirta B. JO - Monthly Notices of the Royal Astronomical Society VL - 343 Y1 - 2003/8/1 SP - 959 EP - 970 KW - galaxies: abundances/ galaxies: evolution/ galaxies: formation/ cosmology: theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.343..959C&db_key=AST&high=42a068d47505048 N2 - We carried out a comprehensive analysis of the chemical properties of the interstellar medium (ISM) and the stellar population (SP) of current normal galaxies and their progenitors in a hierarchical clustering scenario. We compared the results with observations of damped Lyman-alpha systems (DLAs) under the hypothesis that, at least, part of the observed DLAs could originate in the building blocks of present-day normal galaxies. We used a hydrodynamical cosmological code which includes star formation and chemical enrichment. Galaxy-like objects are identified at z= 0 and then followed back in time. Random lines of sight (LOS) are drawn through these structures in order to mimic damped Lyman-alpha systems. We then analysed the chemical properties of the ISM and SP along the LOS. We found that the progenitors of current galaxies in the field with mean L < 0.5L* and virial circular velocity of 100-250 km s^-1 could be the associated DLA galaxies. For these systems we detected a trend for to increase with redshift. We found moderate metallicity evolution for [Zn/H], [Fe/H] and [Si/H]. However, when we applied the observational filter suggested by Boissé et al. (1998) in order to restrict the sample to the observed limits in densities and metallicities, we found mild evolution consistent with observational results that include dust corrections. [Si/Fe] and [S/Fe] show weak alpha-enhancement in agreement with observations corrected by dust depletion. We found alpha/Fe in the ISM and SP to have more homogeneous abundances than [Fe/H] and [Zn/H]. In our models, the global metallicity evolution is driven by the high metallicity and high column density simulated DLAs, which have low impact parameters (b < 5 kpc), and SPs with more than 10⁸ M_solar. Our results suggest that geometrical effects could be the mechanism responsible for the non-detectability of high-metallicity and high-column-density DLAs. We found sub-DLAs to map preferentially the outskirts of the simulated DLA galaxies. Hence, they can contribute to the study of the metallicity of the galactic structure as a function of redshift. An analysis of the metallicity content of the ISMs and SPs of the galaxy-like objects as a function of redshift shows the formation of a central stellar mass concentration with nearly solar metallicity at all redshifts while stars in the outer parts of these objects have lower metallicities. The gas content becomes enriched progressively with redshift and at all radii. The abundance properties of the galaxy-like objects and the simulated DLAs are the results of the contribution of type Ia and II supernovae and gas infall from the dark matter haloes with a timing settled by their particular evolution history in a hierarchical clustering scenario. Our results suggest that the mild evolution detected in the observations could arise from a conspiracy of all of these processes. ER - TY - Journal T1 - Chemical Enrichment of the Intra-Cluster Medium A1 - Cora, SofÍa A. A1 - White, Simon D. M. JO - Astrophysics and Space Science VL - 284 Y1 - 2003/1/1 SP - 425 EP - 428 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Ap%26SS.284..425C&db_key=AST&high=42a068d47505048 N2 - We investigate the metal enrichment of the intra-cluster medium by using a method that combines N-Body simulations and a semi-analytic model (SAM) of galaxy formation. The cluster of galaxies is simulated in a flat, low density universe, with a numerical resolution that allows the detection of substructures in the dark matter background of the cluster. The phenomenological approach used to model the physical processes involved in the galaxy formation and metal production is applied to the substructures found in the dark matter halos detected at different redshifts. Details of the chemical implementation in the SAM and first results related to the mean properties of the baryonic matter components are presented. ER - TY - Journal T1 - On the Effect of Chaotic Orbits on Dynamical Friction A1 - Cora, Sofía A. A1 - Vergne, M. Marcela A1 - Muzzio, Juan C. JO - Astrophysical Journal VL - 546 Y1 - 2001/1/1 SP - 165 EP - 175 KW - Galaxies: Interactions/ Galaxies: Kinematics and Dynamics/ Methods: Numerical UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...546..165C&db_key=AST&high=42a068d47505048 N2 - Chaotic orbits suffer significant changes as a result of small perturbations. One can thus wonder whether the dynamical friction suffered by a satellite on a regular orbit, and interacting with the stars of a galaxy, will be different if the bulk of the stars of the galaxy are in regular or chaotic orbits. In order to check that idea, we investigated the orbital decay (caused by dynamical friction) of a rigid satellite moving within a larger stellar system (a galaxy) whose potential is nonintegrable. We performed numerical experiments using two kinds of triaxial galaxy models: (1) the triaxial generalization of Dehnen's spherical mass model (Dehnen; Merritt & Fridman); (2) a modified Satoh model (Satoh; Carpintero, Muzzio, & Wachlin). The percentages of chaotic orbits present in these models were increased by perturbing them. In the first case, a central compact object (black hole) was introduced; in the second case, the perturbation was produced by allowing the galaxy to move on a circular orbit in a logarithmic potential. The equations of motion were integrated with a non-self-consistent code. Our results show that the presence of chaotic orbits does not affect significantly the orbital decay of the satellite. ER - TY - Journal T1 - The Evolution Of The Star Formation Rate In Galaxies A1 - Cora, SofÍa Alejandra A1 - Muriel, Hernán A1 - Tissera, Patricia Beatriz A1 - GarcÍa Lambas, Diego A1 - Mosconi, Mirta Beatriz JO - Astrophysics and Space Science Supplement VL - 277 Y1 - 2001/1/1 SP - 575 EP - 575 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApSSS.277..575C&db_key=AST&high=42a068d47505048 N2 - Not Available ER - TY - Journal T1 - Orbital decay of galactic satellites as a result of dynamical friction A1 - Cora, Sofia A. A1 - Muzzio, Juan C. A1 - Vergne, M. Marcela JO - Monthly Notices of the Royal Astronomical Society VL - 289 Y1 - 1997/8/1 SP - 253 EP - 262 KW - METHODS: NUMERICAL/ GALAXIES: CLUSTERS: GENERAL/ GALAXIES: GENERAL/ GALAXIES: INTERACTIONS/ GALAXIES: KINEMATICS AND DYNAMICS/ GALAXIES: STRUCTURE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997MNRAS.289..253C&db_key=AST&high=42a068d47505048 N2 - We used N-body numerical simulations to investigate the orbital decay, caused by dynamical friction, of a satellite system (such as a globular cluster or a dwarf galaxy) which moves within a larger spherical stellar system (such as a galaxy). In our experiments the galaxies were simulated with mass points distributed in Plummer spheres with isotropic velocity distribution; those galaxies were self-consistent in some of our simulations, while in others the point masses moved in a rigid Plummer potential without interacting with each other. Satellites were represented with single rigid Plummer distributions that interacted with all the point masses making up the galaxies, and they moved along elongated orbits similar to those of galactic objects. We were particularly interested in low-mass satellites, and most of our investigation dealt with satellite masses of 0.005 and 0.01 of the galactic mass; to ascertain the limitations to the applicability of our results posed by the value of the satellite mass we also analysed several cases with larger masses (0.04 and 0.09). Our numerical results for low-mass satellites showed very good agreement with theoretical predictions obtained from a straightforward application of Chandrasekhar's dynamical friction equation, and allowed us to obtain approximate values of the Coulomb logarithm from the best possible fit between numerical and theoretical results. The structure of the galaxies is significantly altered during the orbital decay for satellite masses greater than 0.01, and we investigated those structural changes. Several experiments were done in order to determine the mechanism involved (local or global) in the satellite orbital decay. The results suggest that for the low mass satellites the orbital decay is mainly due to the dynamical friction, which is itself a local process, and that it is not affected by the global response induced in the galaxy. ER - TY - Journal T1 - The rate of period change in pulsating DB white dwarf stars A1 - Córsico, A. H. A1 - Althaus, L. G. JO - Astronomy and Astrophysics VL - 428 Y1 - 2004/12/1 SP - 159 EP - 170 KW - dense matter/ stars: evolution/ stars: white dwarfs/ stars: oscillations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...428..159C&db_key=AST&high=42a068d47504913 N2 - In this work, we present the theoretically expected rates of pulsation period change for V777 Her (DBV) variable stars. To this end we employ new evolutionary models representative of pulsating DB white dwarf stars computed in a self-consistent way with the predictions of time-dependent element diffusion. At the hot edge of the DB instability strip, the envelopes of the models are characterized by a diffusion-induced double-layered chemical structure. We compute the numerical values of rates of period change by solving the equations of linear, adiabatic, nonradial stellar oscillations. We examine the effects of varying the stellar mass, the mass of the helium envelope and the neutrino emission on the expected period changes. We present extensive tabulations of our results which could be useful for comparison with future detections of the rate of period change in pulsating DB white dwarfs. ER - TY - Journal T1 - Pulsations of massive ZZ Ceti stars with carbon/oxygen and oxygen/neon cores A1 - Córsico, A. H. A1 - García-Berro, E. A1 - Althaus, L. G. A1 - Isern, J. JO - Astronomy and Astrophysics VL - 427 Y1 - 2004/12/1 SP - 923 EP - 932 KW - stars: evolution/ stars: white dwarfs/ stars: oscillations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...427..923C&db_key=AST&high=42a068d47504913 N2 - We explore the adiabatic pulsational properties of massive white dwarf stars with hydrogen-rich envelopes and oxygen/neon and carbon/oxygen cores. To this end, we compute the cooling of massive white dwarf models for both core compositions taking into account the evolutionary history of the progenitor stars and the chemical evolution caused by time-dependent element diffusion. In particular, for the oxygen/neon models we adopt the chemical profile resulting from repeated carbon-burning shell flashes expected in very massive white dwarf progenitors. For carbon/oxygen white dwarfs we consider the chemical profiles resulting from phase separation upon crystallization. For both compositions we also take into account the effects of crystallization on the oscillation eigenmodes. We find that the pulsational properties of oxygen/neon white dwarfs are noticeably different from those made of carbon/oxygen, thus making asteroseismological techniques a promising way to distinguish between the two types of stars and, hence, to obtain valuable information about their progenitors. ER - TY - Journal T1 - The effects of element diffusion on the pulsational properties of variable DA white dwarf stars A1 - Córsico, A. H. A1 - Benvenuto, O. G. A1 - Althaus, L. G. A1 - Serenelli, A. M. JO - Monthly Notices of the Royal Astronomical Society VL - 332 Y1 - 2002/5/1 SP - 392 EP - 398 KW - stars: evolution/ stars: interiors/ stars: oscillations/ white dwarfs UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.332..392C&db_key=AST&high=42a068d47504913 N2 - We explore the effects of element diffusion due to gravitational settling and thermal and chemical diffusion on the pulsational properties of DA white dwarfs. To this end, we employ an updated evolutionary code coupled with a pulsational, finite difference code for computing the linear, non-radial g-modes in the adiabatic approximation. We follow the evolution of a 0.55-M_solar white dwarf model in a self-consistent way with the evolution of chemical abundance distribution as given by time-dependent diffusion processes. Results are compared with the standard treatment of diffusive equilibrium in the trace element approximation. Appreciable differences are found between the two employed treatments. We conclude that time-dependent element diffusion plays an important role in determining the whole oscillation pattern and the temporal derivative of the periods in DAV white dwarfs. In addition, we discuss the plausibility of the standard description employed in accounting for diffusion in most white dwarf asteroseismological studies. ER - TY - Journal T1 - The mode trapping properties of full DA white dwarf evolutionary models A1 - Córsico, A. H. A1 - Althaus, L. G. A1 - Benvenuto, O. G. A1 - Serenelli, A. M. JO - Astronomy and Astrophysics VL - 387 Y1 - 2002/5/1 SP - 531 EP - 549 KW - stars: evolution/ stars: interiors/ stars: white dwarfs/ stars: oscillations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...387..531C&db_key=AST&high=42a068d47504913 N2 - An adiabatic, non-radial pulsation study of a 0.563 M_sun DA white dwarf model is presented on the basis of new evolutionary calculations performed in a self-consistent way with the predictions of time dependent element diffusion, nuclear burning and the history of the white dwarf progenitor. Emphasis is placed on the role played by the internal chemical stratification of these new models in the behaviour of the eigenmodes, and the expectations for the full g-spectrum of periods. The implications for the mode trapping properties are discussed at length. In this regard, we find that, for high periods, the viability of mode trapping as a mode selection mechanism is markedly weaker for our models, as compared with the situation in which the hydrogen-helium transition region is treated assuming equilibrium diffusion in the trace element approximation. ER - TY - Journal T1 - A New Code for Nonradial Stellar Pulsations and its Application to Low-Mass, Helium White Dwarfs A1 - Córsico, A. H. A1 - Benvenuto, O. G. JO - Astrophysics and Space Science VL - 279 Y1 - 2002/1/1 SP - 281 EP - 300 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Ap%26SS.279..281C&db_key=AST&high=42a068d47504913 N2 - We present a finite difference code intended for computing linear, adiabatic, nonradial pulsations of spherical stars. This code is based on a slight modification of the general Newton-Raphson technique in order to handle the relaxation of the eigenvalue (square of the eigenfrequency) of the modes and their corresponding eigenfunctions. This code has been tested computing the pulsation spectra of polytropic spheres finding a good agreement with previous work. Then, we have coupled this code to our evolutionary code and applied it to the computation of the pulsation spectrum of a low mass, pure-helium white dwarf of 0.3 M_solar for a wide range of effective temperatures. In making this calculation we have taken an evolutionary time step short enough such that eigenmodes corresponding to a given model are used as initial approximation to those of the next one. Specifically, we have computed periods, period spacing, eigenfunctions, weight functions, kinetic energies and variational periods for a wide range of modes. To our notice this is the first effort in studying the pulsation properties of helium white dwarfs. The solution we have found working with these realistic white dwarf models are in good accord with the predictions of the asymptotic theory of Tassoul (1980) for high order modes. This indicates that the code presented here is able to work adequately also with realistic stellar models. ER - TY - Journal T1 - New DA white dwarf evolutionary models and their pulsational properties A1 - Córsico, A. H. A1 - Althaus, L. G. A1 - Benvenuto, O. G. A1 - Serenelli, A. M. JO - Astronomy and Astrophysics VL - 380 Y1 - 2001/12/1 SP - L17 EP - L20 KW - STARS: EVOLUTION/ STARS: INTERIORS/ STARS: WHITE DWARFS/ STARS: OSCILLATIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...380L..17C&db_key=AST&high=42a068d47504913 N2 - In this letter we investigate the pulsational properties of ZZ Ceti stars on the basis of new white dwarf evolutionary models calculated in a self-consistent way with the predictions of time dependent element diffusion and nuclear burning. In addition, full account is taken of the evolutionary stages prior to the white dwarf formation. Emphasis is placed on the trapping properties of such models. By means of adiabatic, non-radial pulsation calculations, we find, as a result of time dependent diffusion, a much weaker mode trapping effect, particularly for the high-period regime of the pulsation g-spectrum. This result is valid at least for models with massive hydrogen-rich envelopes. Thus, mode trapping would not be an effective mechanism to explain the fact that all the high periods expected from standard models of stratified white dwarfs are not observed in the ZZ Ceti stars. ER - TY - Journal T1 - The potential of the variable DA white dwarf G117-B15A as a tool for fundamental physics A1 - Córsico, A. H. A1 - Benvenuto, O. G. A1 - Althaus, L. G. A1 - Isern, J. A1 - García-Berro, E. JO - New Astronomy VL - 6 Y1 - 2001/6/1 SP - 197 EP - 213 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001NewA....6..197C&db_key=AST&high=42a068d47504913 N2 - White dwarfs are well studied objects. The relative simplicity of their physics allows one to obtain very detailed models which can be ultimately compared with their observed properties. Among white dwarfs there are specific classes of stars, known as ZZ-Ceti objects, which have a hydrogen-rich envelope and show periodic variations in their light curves. G117-B15A belongs to this particular set of stars. The luminosity variations have been successfully explained as due to /g-mode pulsations. G117-B15A has recently claimed to be the most stable optical clock ever found, being the rate of change of its 215.2 s period very small: PÌ‡=(2.3+/-1.4)×10^-15 ss^-1, with a stability comparable to that of the most stable millisecond pulsars. The rate of change of the period is closely related to its cooling timescale, which can be accurately computed. In this paper we study the pulsational properties of G117-B15A and we use the observed rate of change of the period to impose constraints on the axion emissivity and thus, to obtain a preliminary upper bound to the mass of the axion. This upper bound turns out to be 4 cos²betameV at the 95% confidence level. Although there are still several observational and theoretical uncertainties, we conclude that G117-B15A is a very promising stellar object to set up constraints on particle physics. ER - TY - Journal T1 - LSS 1135: An O-type spectroscopic binary in the galactic OB association Bochum 7 A1 - Corti, M. A1 - Niemela, V. A1 - Morrell, N. JO - Astronomy and Astrophysics VL - 405 Y1 - 2003/7/1 SP - 571 EP - 575 KW - Galaxy: open clusters and associations: individual: Bochum 7 (Vela OB 3)/ stars: binaries: spectroscopic/ stars: early-type UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...405..571C&db_key=AST&high=42a068d47506607 N2 - From radial velocities derived from optical spectroscopic observations performed at CTIO, Chile, and CASLEO, Argentina, we have discovered that LSS 1135 is a single-lined O-type binary system with an orbital period of 2.7532 days. We present an analysis of the orbital elements of this system based on radial velocities of the He absorption lines. We classify the spectrum of LSS 1135 as O6.5V((f)). We also present spectral classifications and radial velocities for other seven OB stars in the region of Bochum 7, an OB association to which LSS 1135 belongs. Our data indicate a distance of 5.0 kpc for this star group. ER - TY - Journal T1 - Optical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205 A1 - Morrell, N. I. A1 - Barbá, R. H. A1 - Niemela, V. S. A1 - Corti, M. A. A1 - Albacete Colombo, J. F. A1 - Rauw, G. A1 - Corcoran, M. A1 - Morel, T. A1 - Bertrand, J.-F. A1 - Moffat, A. F. J. A1 - St-Louis, N. JO - Monthly Notices of the Royal Astronomical Society VL - 326 Y1 - 2001/9/1 SP - 85 EP - 94 KW - BINARIES: GENERAL/ STARS: EARLY-TYPE/ STARS: INDIVIDUAL: HD 93205/ X-RAYS: STARS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.326...85M&db_key=AST&high=42a068d47506607 N2 - A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii lambda4686Å (primary component) and Hei lambda4471Å (secondary component) absorption lines yield semi-amplitudes of 133+/-2 and 314+/-2kms^-1 for each binary component, resulting in minimum masses of 31 and 13M_solar (q=0.42). We also confirm for the binary components the spectral classification of O3V+O8V previously assigned. Assuming for the O8V component a `normal' mass of 22-25M_solar we would derive for the primary O3V a mass of `only' 52-60M_solar and an inclination of about 55° for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185+/-16yr using all available radial velocity data sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage are also discussed. ER - TY - Journal T1 - Stability analysis of quiescent prominences using thermodynamic irreversible energy principles A1 - Costa, A. A1 - González, R. A1 - Sicardi Schifino, A. C. JO - Astronomy and Astrophysics VL - 427 Y1 - 2004/11/1 SP - 353 EP - 361 KW - Sun: prominences/ instabilities/ waves UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...427..353C&db_key=AST&high=42a068d47506289 N2 - Using methods of non-equilibrium thermodynamics that extend and generalize the MHD energy principle of Bernstein et al. (1958, Proc. Roy. Soc. A, 244, 17) we develop a formalism in order to analyze the stability properties of prominence models considered as dissipative states i.e. states far form thermodynamic equilibrium. As an example, the criterion is applied to the Kippenhahn-Schlüter model (hereafter K-S) considering the addition of dissipative terms in the coupled system of equations: the balance of energy equation and the equation of motion. We show from this application, that periods corresponding to typical oscillations of the chromosphere and photosphere (3 and 5 min respectively), that were reported as observations of the prominence structure, can be explained as internal modes of the prominence itself. This is an alternative explanation to the one that supposes that the source of these perturbations are the cold foot chromospheric and photospheric basis. ER - TY - Journal T1 - Characterization of Intensity Variations Along Fe XIV Coronal Loops - A Case Study A1 - Costa, Andrea A1 - Stenborg, Guillermo JO - Solar Physics VL - 222 Y1 - 2004/8/1 SP - 229 EP - 245 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004SoPh..222..229C&db_key=AST&high=42a068d47506289 N2 - We discuss a method, and corresponding results, to analyze the dynamics of localized small-scale coronal (post-flare) loops observed with the MICA (Mirror Coronagraph for Argentina) telescope in the well-known green coronal line at 530.3 nm. In particular, we designed a procedure to measure intensity variations along the structure of a loop, both in space and time. The method was applied to a loop on the southwest limb on green-line images taken on October 1st, 2001 with a cadence of about one per minute. Significant coronal variability was detected in a compact loop system suggesting different types of plasma flow. One of them shows a brightening at the top, which moves down along the axis of the loop with mean velocities that suggest scenarios of high-speed plasma flows. The results obtained allow the flow inside coronal structures to be characterized and theoretical descriptions related to different physical scenarios to be compared. ER - TY - Journal T1 - Analysis of the Si II and Si III DR Processes Applied to Stellar Envelopes A1 - Cruzado, Alicia A1 - Ringuelet, Adela E. A1 - Di Rocco, Héctor O. JO - Astrophysical Journal VL - 554 Y1 - 2001/6/1 SP - 571 EP - 577 KW - Atomic Processes/ Infrared: Stars UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...554..571C&db_key=AST&high=42a068d47507914 N2 - In an earlier attempt to explain the observed excess in the IR flux of Be stars, we have analyzed the dielectronic recombination (DR) of Mg II in stellar envelopes and the influence of this atomic process on the stellar flux. In the present paper, we study the DR of other ions with astrophysical significance, namely, Si II and Si III, and reach the conclusion that Si II may also contribute to the IR excess in Be stars. ER - TY - Journal T1 - Dielectronic Recombination of Mg II in Stellar Envelopes A1 - Cruzado, Alicia A1 - di Rocco, Hector O. A1 - Ringuelet, Adela E. JO - Astrophysical Journal VL - 503 Y1 - 1998/8/1 SP - 902 KW - ATOMIC PROCESSES/ INFRARED: STARS/ STARS: EMISSION-LINE/ BE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...503..902C&db_key=AST&high=42a068d47507914 N2 - The aim of the present paper is to discuss the significance, in the infrared continuum of Be stars, of the dielectronic recombination (DR) of Mg II atoms. To accomplish this, we have calculated the emissivity in the lines of Mg I atoms after the process of electron capture has taken place. In order to estimate its influence in the photospheric flux, we have considered the total energy emitted in all lines with lambda 1 <= lambda <= lambda 2, where lambda 1 and lambda 2 define the wavelength ranges of the Johnson system filters. We conclude that the DR of Mg II atoms does actually contribute significantly to the infrared excess observed in Be stars. ER - TY - Journal T1 - Magnetic helicity analysis of an interplanetary twisted flux tube A1 - Dasso, S. A1 - Mandrini, C. H. A1 - Démoulin, P. A1 - Farrugia, C. J. JO - Journal of Geophysical Research (Space Physics) VL - 108j Y1 - 2003/10/1 EP - 1 KW - Interplanetary Physics: Ejecta/ driver gases/ and magnetic clouds/ Interplanetary Physics: Interplanetary magnetic fields/ Solar Physics/ Astrophysics/ and Astronomy: Magnetic fields/ Solar Physics/ Astrophysics/ and Astronomy: Coronal mass ejections/ Space Plasma Physics: Kinetic and MHD theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003JGRA.108j.SSH3D&db_key=AST&high=42a068d47508009 N2 - We compute the magnetic flux and helicity of an interplanetary flux tube observed by the spacecraft Wind on 24-25 October 1995. We investigate how model-dependent are the results by determining the flux-tube orientation using two different methods (minimum variance and a simultaneous fit), and three different models: a linear force-free field, a uniformly twisted field, and a nonforce-free field with constant current. We have fitted the set of free parameters for the six cases and have found that the two force-free models fit the data with very similar quality for both methods. Then, both the comparable computed parameters and global quantities, magnetic flux and helicity per unit length, agree to within 10% for the two force-free models. These results imply that the magnetic flux and helicity of the tube are well-determined quantities, nearly independent of the model used, provided that the fit to the data is good enough. ER - TY - Journal T1 - A parametric study of the influence of ion and electron properties on the excitation of electromagnetic ion cyclotron waves in coronal mass ejections A1 - Dasso, Sergio A1 - Gratton, Fausto T. A1 - Farrugia, Charles J. JO - Journal of Geophysical Research (Space Physics) VL - 108d Y1 - 2003/4/1 EP - 1 KW - Interplanetary Physics: Ejecta/ driver gases/ and magnetic clouds/ Space Plasma Physics: Wave/particle interactions/ Interplanetary Physics: Solar wind plasma/ Space Plasma Physics: Waves and instabilities/ Space Plasma Physics: Kinetic and MHD theory/ UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003JGRA.108d.SSH2D&db_key=AST&high=42a068d47508009 N2 - Interplanetary coronal mass ejections (ICMEs) often possess a negative proton thermal anisotropy, A_p = T_âŠ¥,p/T_∥,p - 1 < 0 (T_∥, T_âŠ¥: parallel and perpendicular temperatures, respectively) so that right-hand polarized electromagnetic ion cyclotron waves (EICWs) may be amplified by a kinetic instability [Farrugia et al., 1998a]. However, in view of the low proton beta of ICMEs, several physical parameters, besides A_p, need to be in the right range to excite this instability with significant growth rates. In this paper we present a parametric study of EICWs aimed at identifying those parameters which are most influential in fostering the emission of these waves in ICME scenarios. We analyze here the influence of: (1) thermal and suprathermal protons, (2) thermal alpha particles (alphas), and (3) thermal electrons. We solve the dispersion relation of EICWs including protons, alphas and electrons, all modeled with bi-Maxwellian distribution functions, and a minority population of suprathermal protons using a kappa function for the velocity component along the field. For physical regimes of ICMEs we find that the instability depends critically on the values of the following parameters: proton beta, proton thermal anisotropy, relative abundance of the suprathermal protons, alpha-to-proton relative abundance, alpha-to-proton temperature ratio, alpha particle thermal anisotropy, electron-to-proton temperature ratio, and thermal anisotropy of electrons. The effect of these parameters on the instability is either direct (when they increase the number of resonant particles) or indirect (when they decrease the phase speed of the wave so that more particles can resonate). Data surveys on EICWs should take into account the whole set of parameters indicated here, since the expected level of wave excitation results from their combined action. The study may be useful in understanding the considerable level of magnetic fluctuations observed in interplanetary CMEs by the Wind spacecraft. ER - TY - Journal T1 - Ring current decay rates of magnetic storms: A statistical study from 1957 to 1998 A1 - Dasso, Sergio A1 - Gómez, Daniel A1 - Mandrini, Cristina H. JO - Journal of Geophysical Research (Space Physics) VL - 107e Y1 - 2002/5/1 EP - 1 KW - Magnetospheric Physics: Ring current/ Magnetospheric Physics: Storms and substorms/ Magnetospheric Physics: Energetic particles/ precipitating/ Magnetospheric Physics: Solar wind/magnetosphere interactions/ Magnetospheric Physics: Current systems (2409)/ UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002JGRA.107e.SMP5D&db_key=AST&high=42a068d47508009 N2 - We perform a statistical study of the decay times for the recovery phase of the 300 most intense magnetic storms that occurred from 1 January 1957 to 31 December 1998. The Dst index in the decaying stage has been fitted by an exponential function, and a very good correlation has been obtained for most of the storms. Statistically representative values for the decay time (tau) are obtained by averaging the most reliable tau values, which resulted from applying a least squares method to the Dst index time series during every recovery phase. The mean value of tau turned out to be ~14 +/- 4 hours. We have also found that for very intense storms (Dst_min < -250 nT) the values of tau tend to decrease as the intensity of the storm increases. ER - TY - Journal T1 - Waves in the proton cyclotron frequency range in the CME observed by wind on August 7-8, 1996: theory and data A1 - Dasso, S. A1 - Farrugia, C. J. A1 - Gratton, F. T. A1 - Lepping, R. P. A1 - Ogilvie, K. W. A1 - Fitzenreiter, R. J. JO - Advances in Space Research VL - 28 Y1 - 2001/1/1 SP - 747 EP - 752 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AdSpR..28..747D&db_key=AST&high=42a068d47508009 N2 - As first discussed by Farrugia et al. (J. Geophys. Res., 103, 6543, 1998), coronal mass ejections (CMEs) may support the excitation of electromagnetic ion cyclotron waves (EICWs). The proton plasma beta, and the electron temperature and anisotropy in the front region (~5 hours, translating to ~6×10⁶ km) of the CME observed by WIND on August 7-8, 1996 favor this possible excitation. Supplementing these measured parameters by other data taken from a survey of CME properties observed by the ISEE 3 spacecraft (Gosling et al., J. Geophys. Res., 92, 8519, 1987), we solve the EICW dispersion relation numerically. We find short e-folding times of EICWs, of the order of 5 min, i.e., much less than the typical evolution time of these ejecta. We suggest that high resolution data will show enhanced power in the 0.5 Hz range. ER - TY - Journal T1 - Circumnuclear Structures in the Interacting Seyfert Galaxy NGC 1241: Kinematics and Optical/Infrared Morphology A1 - Díaz, Rubén J. A1 - Dottori, Horacio A1 - Vera-Villamizar, Nelson A1 - Carranza, Gustavo JO - Astrophysical Journal VL - 597 Y1 - 2003/11/1 SP - 860 EP - 869 KW - Galaxies: Active/ Galaxies: Individual: NGC Number: NGC 1241/ Galaxies: Kinematics and Dynamics/ Galaxies: Spiral/ Galaxies: Structure/ Methods: Numerical/ Techniques: Spectroscopic UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...597..860D&db_key=AST&high=42a068d47510265 N2 - We studied the spiral pattern in the inner 6.5" (1^''=257 pc) central regions of the interacting active nucleus galaxy NGC 1241 using Gemini North Telescope high-resolution K_s- and J-band images and Hubble Space Telescope (HST) Paalpha and H- and (V+R)-band images with high resolution in the range from ~0.1" to ~0.3" along with intermediate to large-scale spectroscopy using the Multifunction Spectrograph at the Córdoba Observatory in Argentina. Our analysis of Paalpha emission images revealed a faint two-armed leading spiral pattern ending in the 5.6"×3.4" clumpy ring discovered by Böker and coworkers, harboring a 1.6" long barlike structure almost perpendicular to the large-scale bar of NGC 1241. When we applied two-dimensional Fourier analysis at circumnuclear scales, we found that a two-arm trailing mode was dominant in K_s- and J-band images while the (V+R)-band images showed more complex structural features with a strong one-armed trailing mode. One-dimensional Fourier analysis showed a corotation (CR) located outward from the edge of the Paalpha bar. Our kinematics data gave an angular speed Omega_CN of 350+/-50 km s^-1 kpc^-1 for the trailing mode pattern. The rotation curve showed that the circumnuclear ring is located just inside the large-scale pattern inner Lindblad resonance (ILR), which has a radius of about r~1 kpc. We also found, within the uncertainties present in such measurements, that the outer Lindblad resonance (OLR) of the circumnuclear pattern is coincident with the large-scale pattern ILR, indicating a possible connection between circumnuclear and global dynamics. Nevertheless, the estimated high molecular gas fraction (>=13%) and the inner pattern high angular speed at the central region of NGC 1241 point to a nuclear bar formation via self-gravitational instability. ER - TY - Journal T1 - Study of MCLeish's Interacting Object A1 - Díaz, R. A1 - Rodrigues, I. A1 - Dottori, H. A1 - Carranza, G. JO - Astronomical Journal VL - 119 Y1 - 2000/1/1 SP - 111 EP - 118 KW - GALAXIES: BINARY/ GALAXIES: INDIVIDUAL (MCLEISH'S OBJECT)/ GALAXIES: INTERACTIONS/ GALAXIES: KINEMATICS AND DYNAMICS/ GALAXIES: NUCLEI/ GALAXIES: PECULIAR UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....119..111D&db_key=AST&high=42a068d47510265 N2 - We discuss the morphology, kinematics, and physical conditions of the emitting gas of the interacting system IRAS 20048-6621. We present as well numerical simulations of this interacting system, discovered by David McLeish in 1946. The main galaxy (McL A) is an edge-on spiral galaxy with highly distorted NW side. On this side is also located McL B, the perturber galaxy. We determined a distance of 151 Mpc (h=0.75) and a diameter of 70 kpc for McL A. It presents a bright nucleus with broad red emission lines (~500 km s^-1). McL A has far-IR color indexes closely comparable to NGC 3628, one the few nearby edge-on galaxies which is a bright infrared emitter. Nevertheless, McL A is more luminous (in these bands) than any of the edge-on galaxies in the sample of bright infrared galaxies of Young et al. (1988). The two sides of McL A rotation curve are remarkably different. The N-body model that best reproduces McL A kinematical and morphological data (Kuijken & Dubinski 1995) gives a total mass 7x10¹¹ M_solar for McL A. Numerical simulations with the TREESPH code closely reproduce the morphology and radial velocity observations. The best scenario for this system is that of a prograde encounter between McL A and B, with McL B's orbit 35 deg tilted with respect to the spiral disk of McL A and a perigalactic distance of 17.6 kpc. The derived mass ratio is McL B/McL A~1/26. In the last 5x10⁸ yr the perturber has crossed the main galaxy disk twice, in between it crossed the perigalacticon. According to our simulations, the emitting gas present in McL B has not been stripped out from the McL A disk, so that leads us to conclude that McL B is an irregular or small spiral galaxy. ER - TY - Journal T1 - Kinematics of the Central Regions of NGC 1672 A1 - Díaz, R. A1 - Carranza, G. A1 - Dottori, H. A1 - Goldes, G. JO - Astrophysical Journal VL - 512 Y1 - 1999/2/1 SP - 623 EP - 629 KW - GALAXIES: ACTIVE/ GALAXIES: INDIVIDUAL (NGC 1672)/ GALAXIES: KINEMATICS AND DYNAMICS/ GALAXIES: NUCLEI UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...512..623D&db_key=AST&high=42a068d47510265 N2 - We present the detailed velocity field of the central 2 kpc of the LINER galaxy NGC 1672. The isovelocity map shows a rotational pattern with a velocity gradient of 50 km s^-1 arcsec^-1 in the inner 6" (1^''~70 pc), indicating a mass of ~9x10^8 M_solar inside a radius of 125 pc, equivalent to a density of ~2x10^11 M_solar kpc^-3. It also shows some asymmetries on a larger scale. An offset of ~60 pc between the nuclear continuum barycenter and the kinematical center is also found. Satoh's model fitting to the observed velocity field reveals several nonaxisymmetric residuals, which do not correlate well with the bar or the circumnuclear ring of H II regions. The inner rotation curve of NGC 1672 reveals that the circumnuclear ring of star formation is located on an inner Lindblad resonance (ILR), and not near the peak of the Lindblad curve, Omega-kappa/2, as suggested by previous works, which also claimed that the ring rotates faster than its ambient. This motion is not confirmed by the two-dimensional residual-velocity map. ER - TY - Journal T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: galaxy spectral type segregation in groups A1 - Domínguez, M. J. A1 - Zandivarez, A. A. A1 - Martínez, H. J. A1 - Merchán, M. E. A1 - Muriel, H. A1 - Lambas, D. G. JO - Monthly Notices of the Royal Astronomical Society VL - 335 Y1 - 2002/9/1 SP - 825 EP - 830 KW - stars: formation/ galaxies: clusters: general/ galaxies: evolution/ galaxies: fundamental parameters/ galaxies: stellar content UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.335..825D&db_key=AST&high=42a068d47512048 N2 - The behaviour of the relative fraction of galaxies with different spectral types in groups is analysed as a function of projected local galaxy density and the group-centric distance. The group sample was taken from the 2dF Group Galaxy Calatogue constructed by Merchán & Zandivarez. Our group sample was constrained to have a homogeneous virial mass distribution with redshift. Galaxies belonging to this group sample were selected in order to minimize possible biases, such as preferential selection of high-luminosity objects. We find a clear distinction between high virial mass groups (M_V>~ 10^13.5 M_solar) and the less massive ones. While the massive groups show a significant dependence of the relative fraction of low star formation galaxies on local galaxy density and group-centric radius, groups with lower masses show no significant trends. We also cross-correlate our group subsample with the previously identified clusters, finding that this sample shows a very similar behaviour to that observed in the high virial mass group subsample. ER - TY - Journal T1 - Galaxy Morphological Segregation in Clusters: Local versus Global Conditions A1 - Domínguez, Mariano A1 - Muriel, Hernán A1 - Lambas, Diego G. JO - Astronomical Journal VL - 121 Y1 - 2001/3/1 SP - 1266 EP - 1274 KW - Galaxies: Clusters: General/ Galaxies: Evolution/ Galaxies: Fundamental Parameters/ Galaxies: Intergalactic Medium/ X-Rays UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121.1266D&db_key=AST&high=42a068d47512048 N2 - We study the relative fraction of galaxy morphological types in clusters as a function of the projected local galaxy density and of different global parameters: cluster projected gas density, cluster projected total mass density, and reduced cluster-centric distance. Since local and global densities are correlated, we have considered different tests to search for the parameters on which segregation shows the strongest dependence. We have also explored the results of our analysis as they apply to both the central regions of the clusters and their outskirts. We consider a sample of clusters of galaxies with estimated temperatures and derive the projected mass density profile, using the model of Navarro, Frenk, & White, and the 500 overdensity contrast radius (r₅₀₀), using the scaling relation. X-ray surface brightness profiles are used to obtain the projected gas density, assuming the hydrostatic equilibrium model. Our results suggest that morphological segregation in clusters is controlled by local galaxy density in the outskirts. On the other hand, global projected mass density shows the strongest correlation with the fractions of morphological types in the central high-density region, with a marginal dependence on local galaxy density. ER - TY - Journal T1 - On the nature of the galaxy NGC 5666 A1 - Donzelli, C. J. A1 - Davoust, E. JO - Astronomy and Astrophysics VL - 409 Y1 - 2003/10/1 SP - 91 EP - 97 KW - galaxies: photometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...409...91D&db_key=AST&high=42a068d47513285 N2 - We present B and R CCD images and optical spectroscopy in the range 3700-8900 Å for the galaxy NGC 5666, which until now was considered as a low-luminosity elliptical. The high-resolution images show a conspicuous spiral pattern which is limited to the inner region (r <=5arcsec , or 1/6 of the isophotal radius) and a faint (presumably tidal) outer feature dotted with small knots resembling star clusters or tidal dwarf galaxies. The patchy spiral structure and the luminosity profiles suggest a late-type morphological type, but the disk is of high central surface brightness and the bulge weak and very extended. The nuclear spectrum reveals typical emission lines found in late-type galaxies, but the underlying nuclear stellar population and continuum only match that of an elliptical galaxy combined with a young (<1 Gyr) stellar population. These and other properties of the galaxy suggest that this could be a minor merger, at an intermediate stage, between a gas-rich dwarf and a small early-type disk galaxy. If this is the case, the galaxy NGC 5666 will provide important constraints to the theory of hierarchical galaxy formation. ER - TY - Journal T1 - Spectroscopic Observations of Merging Galaxies A1 - Donzelli, C. J. A1 - Pastoriza, M. G. JO - Astronomical Journal VL - 120 Y1 - 2000/7/1 SP - 189 EP - 202 KW - Galaxies: Interactions/ Galaxies: Nuclei/ Galaxies: Seyfert UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....120..189D&db_key=AST&high=42a068d47513285 N2 - In this paper we describe the spectroscopic and infrared properties of a sample of 25 merging galaxy pairs, selected from the catalog of Arp & Madore, and we compare them with those observed in a similar sample of interacting galaxies (Donzelli & Pastoriza). It is noted that mergers as well as interacting systems comprise a wide range of spectral types, going from those corresponding to well-evolved stellar populations (older than 200 Myr) to those that show clear signatures of H II regions with stellar populations younger than 8 Myr. However, merger galaxies show on average more excited spectra than interacting pairs, which could be attributed to lower gas metallicity. From the emission lines we also found that merging systems show on average higher (about a factor of 2) star formation rates than interacting galaxies. Classical diagnostic diagrams show that only three of 50 of the galaxies (6%) present some form of nuclear activity: two Seyfert galaxies and one LINER. However, through a detailed analysis of the pure emission-line spectra, we conclude that this fraction may raise up to 23% of the mergers if we consider that some galaxies host a low-luminosity active nucleus surrounded by strong star-forming regions. This latter assumption is also supported by the infrared colors of the galaxies. Regarding to the total infrared luminosities, the merging galaxies show on average an IR luminosity, log(L_ir)=10.7, lower than that of interacting systems, log(L_ir)=10.9. We find that only three mergers of the sample (12%) can be classified as luminous infrared galaxies, while this fraction increases to 24% in the interacting sample. Based on observations made at CASLEO. Complejo Astronómico El Leoncito is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan. ER - TY - Journal T1 - Imaging and spectroscopy of ten southern galaxies selected from a catalogue of peculiar galaxies A1 - Donzelli, C. J. A1 - Ferreiro, D. L. JO - Astronomy and Astrophysics Supplement Series VL - 127 Y1 - 1998/2/1 SP - 527 EP - 542 KW - GALAXIES: PECULIAR/ GALAXIES: PHOTOMETRY/ GALAXIES: STARBURST/ GALAXIES: INTERACTIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..127..527D&db_key=AST&high=42a068d47513285 N2 - We present BVRI broad band photometry and long slit spectroscopy for a sample of ten southern galaxies selected from the Aguero Catalogue of Peculiar Galaxies. The analysis of the images shows that only four galaxies of the sample are truly peculiar galaxies and four are normal spirals. The remaining two galaxies, a normal spiral and a SO, form an interacting pair. Despite the rather complicated structure of the peculiar galaxies we did not find evidence of mergers in our analysis of images and rotation curves. Almost all galaxies in our sample show star forming regions with very blue colors, (B-V) ranging from 0.2 to 0.6. The SO galaxy shows a very interesting structure in the V-I color map suggesting that star formation events have occurred in concentric annuli centered in the nucleus. In our photometric analysis we did not find characteristics that could distinguish between normal and peculiar galaxies. We obtained the ``pure-emission'' line spectra for six galaxies of the sample by subtracting appropriate templates. These templates correspond to ellipticals selected from our library of spectra. This subtraction technique provides a powerful tool to calculate line flux ratios uncontaminated by the underlying stellar population. Our spectroscopic analysis confirms that the spiral galaxy of the interacting system AM 2054-433 has a LINER-type nucleus. In the normal galaxy ESO 316-29 we find evidence of a LINER nucleus and we report a new Seyfert 2 galaxy, AM 2054-433 N. For this SO galaxy the line flux ratios measured from the pure-emission spectrum are indicative of a Seyfert 2 rather than a LINER nucleus as it was previously reported by other authors. Three of the four peculiar galaxies in our sample have much higher star-formation rate than normal galaxies, as measured by Halpha + [NII] line emission. The observed EW(Halpha + [NII]) values for these peculiar galaxies are around 60 Angstroms, compared to 22 Angstroms for normal galaxies. Whole-aperture spectra for these peculiar galaxies show very similar EW(Halpha + [NII]) values to those observed in their nuclear region suggesting that a global starburst has occurred. Although our sample is small the results presented suggest that peculiar morphology and global starburst events are closely related. ER - TY - Journal T1 - Optical Spectroscopic Properties of a Sample of Interacting Galaxies A1 - Donzelli, C. J. A1 - Pastoriza, M. G. JO - Astrophysical Journal Supplement Series VL - 111 Y1 - 1997/7/1 SP - 181 KW - GALAXIES: INTERACTIONS/ GALAXIES: PHOTOMETRY/ GALAXIES: SEYFERT/ GALAXIES: STELLAR CONTENT UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJS..111..181D&db_key=AST&high=42a068d47513285 N2 - We present spectroscopic observations of 83 galaxies from a sample of 49 pairs of optically selected interacting galaxies, most of them previously unobserved. These pairs consist of a main galaxy (component A) and a companion (component B) that has about half or less the diameter of component A. From our spectra we determine that 27 galaxies form truly physical pairs and seven are apparent pairs, for the remaining pairs we could only extract the spectra of the A components. The spectra of the physical pairs were classified into four groups according to the emission-line spectra observed in each component. These classifications were made because the sample exhibits a very large range of spectral properties, ranging from well-evolved stellar populations (older than 200 Myr) to emission-line--dominated starburst systems (80 Myr or younger). In general terms, these spectral types are well correlated with the morphological types of the galaxies. However, we find no evidence of correlation of the equivalent width of H alpha + [N II] emission lines with the degree of the interaction or with the blue absolute magnitude of the components. From the data it is also determined that the average EW(H alpha + [N II]) for the physical pairs is 37 A for the A components and 54 A for the B components. For the galaxies that form apparent pairs we obtain EW(H alpha + [N II]) = 27 A, confirming that physical pairs have higher mean star formation rates than isolated galaxies. This enhancement of the star formation activity is more likely to take place in both galaxies, but the strength of the activity seems to be higher in the B components. The mean observed values of EW(H alpha + [N II]) are comparable with those observed in a sample of strongly interacting or merging galaxies. On the other hand, we do not find the excess of Seyfert-type nuclei previously reported in studies of similar samples of galaxies. ER - TY - Journal T1 - NGC 6438: A Triple System? A1 - Donzelli, C. J. A1 - Espindola, M. JO - Astronomical Journal VL - 111 Y1 - 1996/3/1 SP - 1057 KW - GALAXIES: INDIVIDUAL: NGC 6438/ GALAXIES: INTERACTIONS/ GALAXIES: IRREGULAR UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996AJ....111.1057D&db_key=AST&high=42a068d47513285 N2 - We provide photographic and photoelectric information as well as CCD imaging and medium resolution spectroscopy on this system located at a distance of ~32 Mpc. The S0 galaxy has twisted isophotes which also show changes in the ellipticity. Profiles toward the north of this galaxy are 0.1 and 0.2 mag brighter in the B and V bands, respectively, than in any other direction, probably due to the presence of dust in the Irregular system. Several blue regions (B-V = 0.26-0.40) are found in the Irregular object indicating ongoing star formation. One of these regions is located in an extreme of the northern arm, its luminosity being similar to that of the nucleus which is very close to it. Analysis of the spectra shows typical absorption lines and a weak [N II] emission in the S0 galaxy, whereas Halpha, [N II], and [S II] emission lines are observed both in the nucleus and in the blue region mentioned above. We determine a high reddening E(B - V) = 1.4 in the nuclear region of this system. Rotation curves show a different behavior for the nucleus and the blue region, which have V_max_ >= 180 km/s and V_max_ = 80 km/s, respectively. All this evidence could support the idea that NGC 6438 is an interacting triplet, one S0 galaxy and two disk galaxies undergoing a merger. ER - TY - Journal T1 - The molecular clouds in the environs of the supernova remnants G349.7+0.2 and G18.8+0.3 A1 - Dubner, G. A1 - Giacani, E. A1 - Reynoso, E. A1 - Parón, S. JO - Astronomy and Astrophysics VL - 426 Y1 - 2004/10/1 SP - 201 EP - 212 KW - ISM: molecules/ ISM: clouds/ ISM: supernova remnants/ radio lines: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...426..201D&db_key=AST&high=42a068d47518159 N2 - We present the results of a new high-resolution study of the molecular gas associated with the supernova remnants (SNRs) G349.7+0.2 and G18.8+0.3. The observations were performed with the SEST telescope in the ¹²CO J = 1-0, 2-1 and 3-2 lines (beams of 45^'', 23^'' and 15^'', respectively). The present observations have provided, for the two SNRs, new evidence in support of the existence of physical interaction between the SN shocks and the adjoining molecular clouds. In the case of G349.7+0.2, the new observations revealed for the first time the internal structure of the shocked cloud, as well as the kinematical consequences of the impact of the SNR shock on the molecular cloud. From these observations we were able to constrain the conditions of the pre-shocked gas. The molecular cloud associated with G349.7+0.2, centered near v_LSR= +16.2 km s^-1, has a linear size of about 7 pc, a mass of ~ 10⁴ M_âŠ™ and a volume density of ~ 10³ cm^-3. The high line ratios derived are indicative of the existence of shocks in the cloud. From the asymmetries observed in the line shapes we propose that the SN shock cloud is running into the denser part of the cloud and has probably begun to disrupt it, pushing the eastern component clumps away from us, and the western fragments toward us. After comparing our estimates of the column density of the intervening gas with similar calculations based on ASCA X-rays spectral fitting we conclude that the best way to make these results compatible is by assuming that the associated cloud is placed behind G349.7+0.2 along the line of sight, and the SNR/molecular cloud encounter is taking place on the far side of the SNR. This model also provides a natural explanation for the lack of strong X-ray absorption in the central region of G349.7+0.2. Evaporation of part of the associated cloud must be responsible for the central X-ray emission. The comparison with IRAS infrared data provides additional support for the hypothesis of SNR/cloud physical interaction. From the study of the molecular gas in the neighborhood of the five OH (1720 MHz) masers detected in G349.7+0.2 we find that in three cases the maser peak velocity coincides with the local CO peak velocity, while in the remaining two cases the maser peak velocity agrees with a secondary, blended CO component. We conclude that the masers are excited at the sites where a non-dissociative C-type shock, locally transverse to the line of sight (or forming a large angle with it), hits a denser molecular clump. For the SNR G18.8+0.3, the new higher resolution observations have revealed excellent morphological agreement between one of the cloud components and the SNR shock front towards the eastern limb. The associated molecular mass is estimated to be ~ 4.4× 10⁴ M_âŠ™ and the cloud volume density ~1200 cm^-3. The analysis of the line ratios in this case revealed a maximum of R_2-1/1-0 = 1.25 at a position that exactly matches an indentation in the radio continuum emission in the remnant's shell, providing additional evidence of SNR/molecular cloud interaction. ER - TY - Journal T1 - The neutral gas environment of the young supernova remnant SN 1006 (G327.6+14.6) A1 - Dubner, G. M. A1 - Giacani, E. B. A1 - Goss, W. M. A1 - Green, A. J. A1 - Nyman, L.-Å. JO - Astronomy and Astrophysics VL - 387 Y1 - 2002/6/1 SP - 1047 EP - 1056 KW - ISM: individual objects: SN 1006/ ISM: individual objects: G327.6+14.6/ ISM: supernova remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...387.1047D&db_key=AST&high=42a068d47518159 N2 - Using the Australia Telescope Compact Array, we have carried out a survey of the H I emission in the direction of the bilateral supernova remnant (SNR) SN 1006 (G327.6+14.6). The angular resolution of the data is 4.7' x 3.0', and the rms noise ~39 mJy/beam (~ 0.3 K). To recover structures at low spatial frequencies, single dish data have been added to the interferometric images. We have also studied the ¹²CO emission in the transitions J=1-0 and J=2-1, looking for very compact clumps of molecular gas as possible sites for the acceleration of electrons and nuclei to TeV energies associated with the gamma -ray source detected on the NE limb of SN 1006. These molecular gas observations produced only marginal detections. From the present observations we conclude that the distribution of the surrounding neutral gas had no strong influence in shaping this SNR with a bilateral appearance. Intrinsic factors may have contributed to the present morphology. The remnant of SN 1006 appears to be evolving in a smooth environment with an atomic volume density n₀ ~ 0.3 cm^-3. The existence of an H I concentration projected on the center of SN 1006 suggests an upper limit of ~-20 km s^-1 on the systemic velocity of the SNR. This limit is compatible with a distance to the SNR of about 1.7 kpc, in good agreement with previous estimates. An extended H I cloud with volume density ~0.5 cm^-3 is detected towards the NW border of SN 1006. This concentration may be responsible for the formation of the bright Balmer filaments observed in SN 1006. The absorbing column density towards SN 1006 has been estimated to be N H ~ 6.8 × 10²⁰ cm^-2, in good agreement with previous suggestions based on X-ray results. ER - TY - Journal T1 - The Interstellar Medium around the Supernova Remnant G320.4-1.2 A1 - Dubner, G. M. A1 - Gaensler, B. M. A1 - Giacani, E. B. A1 - Goss, W. M. A1 - Green, A. J. JO - Astronomical Journal VL - 123 Y1 - 2002/1/1 SP - 337 EP - 345 KW - ISM: individual (G320.4-1.2)/ ISM: individual (RCW 89)/ ISM: Structure/ pulsars: individual (B1509-58)/ ISM: Supernova Remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123..337D&db_key=AST&high=42a068d47518159 N2 - Using the Australia Telescope Compact Array, we have carried out a survey of the H I emission in the direction of the barrel-shaped supernova remnant (SNR) G320.4-1.2 (MSH 15-52) and its associated young pulsar B1509-58. The angular resolution of the data is 4.0'×2.7', and the rms noise is of order 30 mJy beam^-1 (~0.5 K). The H I observations indicate that the north-northwest radio limb has encountered a dense H I filament (density ~12 cm^-3) at the same LSR velocity as that of the SNR (V_LSR~-68 km s^-1). This H I concentration would be responsible for the flattened shape of the northwestern lobe of G320.4-1.2 and for the formation of the radio-optical-X-ray nebula RCW 89. The emission associated with the bright knots in the interior of RCW 89 can be explained as arising from the interaction between the collimated relativistic outflow from the pulsar and the denser part of this H I filament (density ~15 cm^-3). The south-southeastern half of the SNR, on the other hand, seems to have rapidly expanded across a lower density environment (density ~0.4 cm^-3). The H I data also reveal an unusual H I feature aligned with a collimated outflow generated by the pulsar, suggestive of association with the SNR. The anomalous kinematical velocity of this feature (V_LSR~15 km s^-1), however, is difficult to explain. ER - TY - Journal T1 - High-Resolution VLA Imaging of the Supernova Remnant W28 at 328 and 1415 MHZ A1 - Dubner, G. M. A1 - Velázquez, P. F. A1 - Goss, W. M. A1 - Holdaway, M. A. JO - Astronomical Journal VL - 120 Y1 - 2000/10/1 SP - 1933 EP - 1945 KW - ISM: individual (W28)/ Radio Continuum/ ISM: Supernova Remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....120.1933D&db_key=AST&high=42a068d47518159 N2 - We present new VLA images at 328 and 1415 MHz of the supernova remnant (SNR) W28. The image at 1415 MHz, produced after the combination of 50 separate VLA pointings and the addition of single-dish data, has an angular resolution of 88"×48", with an rms noise of 5 mJy beam^-1. At 328 MHz, the image has an angular resolution of 97"×52" and an rms noise of 14 mJy beam^-1. From these observations we reestimated the characteristic parameters of W28: angular diameter 48', flux densities S_{1415 MHz}=246 Jy and S_{328 MHz}=425 Jy, Sigma_{1
GHz}~1.8×10^-20 W m^-2Hz^-1 sr^-1, and alpha=-0.35 (S~nu^alpha). The radio spectrum has local variations which correlate with total intensity features. The brighter radio filaments have a spectral index systematically flatter than the rest. The comparison of the radio emission with images in other spectral ranges reveal several excellent correlations. We conclude that (1) the encounter of the SNR shock with a molecular cloud to the east of W28 produced enhanced synchrotron and thermal X-ray emission, compression and distortion in the radio shell, Halpha filaments, and the excitation of many OH (1720 MHz) masers exactly located in the interface between the shock front and the eastern molecular cloud; and (2) the interaction of the shock front moving toward us with molecular gas located in front of it has been responsible for the formation of the bright radio filaments seen in projection in the northern half of W28 and the excitation of more OH masers. Also, excellent radio/Halpha correspondence is observed toward the northwest of the SNR. The total energy in relativistic particles is estimated in 2×10⁴⁷ ergs. ER - TY - Journal T1 - Interaction of the Supernova Remnant G18.8+0.3 with the Surrounding Medium A1 - Dubner, G. A1 - Giacani, E. A1 - Reynoso, E. A1 - Goss, W. M. A1 - Roth, M. A1 - Green, A. JO - Astronomical Journal VL - 118 Y1 - 1999/8/1 SP - 930 EP - 941 KW - ISM: CLOUDS/ ISM: H I/ ISM: INDIVIDUAL (G18.8+0.3=KESTEVEN 67)/ ISM: MOLECULES/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....118..930D&db_key=AST&high=42a068d47518159 N2 - We have carried out a study of the interaction of the supernova remnant (SNR) G18.8+0.3 with the surrounding interstellar medium. Observations of the H I, ^12CO, ^13CO, and OH (1720 MHz) lines were performed toward a large field around G18.8+0.3 using the Parkes (Australia) 64 m single-dish telescope, the 4 m NANTEN millimetric telescope (Las Campanas Observatory, Chile), and the Very Large Array (NRAO). The present survey has revealed the existence of an elongated molecular cloud (about 21^'x6^' in size) adjacent to the more flattened borders of the SNR and to the far side of the remnant. The overall CO and H I morphology and kinematics allow us to conclude that the explosion occurred near the border of a preexisting molecular cloud, driving a slow shock into the cloud. The presence of diffuse shock-heated dust with a color temperature of about 30 K was shown in coincidence with the molecular feature using IRAS data. The shocked CO and H I gas was detected between +10 and +27 km s^-1 (LSR). The systemic velocity of this complex, about +19 km s^-1, yields a kinematic distance of about 1.9 kpc for G18.8+0.3. The shock is presently expanding into the cloud at ~10 km s^-1. Masses of the order of 7300, 1100, and 55 M_solar are estimated for the associated molecular hydrogen, atomic hydrogen, and heated dust, respectively. The total kinetic energy transferred by the supernova shock to the surrounding interstellar medium is of the order of 10^49 ergs. An age of ~16,000 yr is calculated for G18.8+0.3. The extended molecular feature with a density of ~600 cm^-3 has denser clumps immersed in it, with densities ranging from ~2500 to ~6000 cm^-3. Three out of five of these clumps were found to contain luminous IRAS pointlike sources compatible with protostellar candidates, suggesting a causal relationship with the supernova explosion that deserves further investigation. The interferometric search for OH (1720 MHz) masers gave negative results. These OH masers can be short-lived occurrences and dissipate quickly in the cooling postshock gas because of the very restrictive conditions under which masers form. Therefore, their absence does not preclude the hypothesis of shock-cloud interaction. ER - TY - Journal T1 - A High-Resolution Radio Study of the W50-SS 433 System and the Surrounding Medium A1 - Dubner, G. M. A1 - Holdaway, M. A1 - Goss, W. M. A1 - Mirabel, I. F. JO - Astronomical Journal VL - 116 Y1 - 1998/10/1 SP - 1842 EP - 1855 KW - ISM: H I/ ISM: INDIVIDUAL: ALPHANUMERIC: W50/ ISM: JETS AND OUTFLOWS/ RADIO CONTINUUM/ STARS: INDIVIDUAL: ALPHANUMERIC: SS 433/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116.1842D&db_key=AST&high=42a068d47518159 N2 - We present VLA images at 327.5 and 1465 MHz of the nebula W50 surrounding the stellar source of relativistic jets SS 433. At 1.4 GHz, we have produced an image of W50 with an angular resolution of 55" that contains all the spatial structures. The technique consists of a complex combination of 58 separate VLA pointings plus the addition of single-dish data into a single mosaic. For the first time, this high-quality radio image has revealed the puzzling structure of W50, which resembles a seashell. The present data confirm the connection between the subarcsecond relativistic jets from SS 433 and the extended nebula W50 over ~5 orders of magnitude in scale. The central component can be very accurately described by a circle 58' in diameter. The eastern wing exhibits a clear helical pattern that mirrors at larger scales the precession of the jets from SS 433. The western wing, smaller and brighter than its eastern counterpart, has a bright bowed arch at the edge, in the region where the structure appears to interact with a higher density medium. The spectral index of the radio continuum emission exhibits striking asymmetries: the central spherical component has a quite normal spectrum for shell-type supernova remnants, alpha ~ 0.5 (S ~ nu^-alpha), while it steepens toward the eastern wing (alpha ~ 0.8) and flattens toward the western one (alpha ~ 0.4). A ``chimney,'' apparently radiating away from W50, is observed in the eastern wing. The atomic hydrogen emission was surveyed in an area of 4 deg x 4 deg around W50 using the NRAO Green Bank 140 foot (43 m) telescope. Based on these observations, unmistakable evidence of an interaction of W50 with the surrounding H i gas at the systemic radial velocity v = 42 km s^-1 is found. Clear traces of the interaction of the jets of SS 433 with the surrounding gas are shown. Based on these observations a kinematic distance of 3 kpc is determined for the W50-SS 433 system. An elliptical shell of ~30,000 M_âŠ™, expanding at about 76 km s^-1, can be associated with the radio nebula. The kinetic energy transferred into the ambient medium is estimated (~2 x 10^51 ergs), thus confirming that the relativistic jets from SS 433 represent an important contribution to the overall energy budget of W50. ER - TY - Journal T1 - Neutral Hydrogen in the Direction of the VELA Supernova Remnant A1 - Dubner, G. M. A1 - Green, A. J. A1 - Goss, W. M. A1 - Bock, D. C.-J. A1 - Giacani, E. JO - Astronomical Journal VL - 116 Y1 - 1998/8/1 SP - 813 EP - 822 KW - ISM: H I/ ISM: INDIVIDUAL: NAME: VELA SUPERNOVA REMNANT/ ISM: STRUCTURE/ RADIO CONTINUUM/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116..813D&db_key=AST&high=42a068d47518159 N2 - We have carried out a study of the distribution and kinematics of the neutral hydrogen in the direction of the Vela supernova remnant (SNR). A field of 6.8d x 5.4d centered at l = 264.1d, b = -1.6d was surveyed using the Parkes 64 m radio telescope (half-power beamwidth 14.7' at 21 cm). Nearly 2300 H i profiles were obtained with a grid spacing of 7.5'. The presence of a thin, almost circular H i shell, centered at v = 1.6 +/- 0.8 km s^-1, is revealed. This shell delineates the outer border of the X-ray emission as shown in the ROSAT observations of Aschenbach, Egger, & Trümper and wraps around the receding part of the remnant. In addition, two higher velocity features possibly associated with Vela are observed at about -30 and 30 km s^-1. These features are interpreted as gas accelerated by the expansion of the supernova shock. The low systemic velocity observed suggests a distance shorter than 500 pc for the Vela SNR. The H i shell is ~7 deg in diameter and expands at v ~ 30 km s^-1. By assuming a distance of 350 pc, we calculate for this shell a linear radius of 22 pc, a swept-up mass of ~1200-2300 M_âŠ™, and an atomic preshock density of ~1-2 cm^-3. The kinetic energy transferred by the supernova shock into the interstellar medium is ~(1-2) x 10^49 ergs, while the initial energy of the explosion is estimated to be ~(1-2.5) x 10^51 ergs. We present the distribution of the column density of the neutral material absorbing the X-radiation, an essential parameter in the analysis of X-ray data. A comparison between the H i and Halpha emission suggests that the H i shell contains embedded dust that might be responsible for increased optical absorption in this region. On the other hand, the brightest arc-shaped optical filaments associated with the western side of Vela show good correspondence with the H i features. From a comparison between the H i and Molonglo Observatory Synthesis Telescope 843 MHz radio continuum emission, we find that the outermost arched radio filaments correlate well with the main ridge of the H i shell. No strong inhomogeneities were found in the ambient H i medium in the direction of Vela X (the central nebula, powered by the pulsar PSR B0833-45). ER - TY - Journal T1 - VLA Observations of Nine Galactic Supernova Remnants A1 - Dubner, G. M. A1 - Giacani, E. B. A1 - Goss, W. M. A1 - Moffett, D. A. A1 - Holdaway, M. JO - Astronomical Journal VL - 111 Y1 - 1996/3/1 SP - 1304 KW - SUPERNOVA REMNANTS/ ACCELERATION OF PARTICLES/ MAGNETIC FIELDS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996AJ....111.1304D&db_key=AST&high=42a068d47518159 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1304D&db_key=AST ER - TY - Journal T1 - Mineralogical characterization of some basaltic asteroids in the neighborhood of (4) Vesta: first results A1 - Duffard, René A1 - Lazzaro, Daniela A1 - Licandro, Javier A1 - de Sanctis, Maria Cristina A1 - Capria, Maria Teresa A1 - Carvano, Jorge M. JO - Icarus VL - 171 Y1 - 2004/9/1 SP - 120 EP - 132 KW - Asteroids/ Vesta/ composition/ asteroids UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Icar..171..120D&db_key=AST&high=42a068d47518458 N2 - We present reflectance spectra of 19 V-type asteroids obtained at the 3.6 m Telescopio Nazionale Galileo covering 0.8 to 2.5 mum. For 8 of these asteroids we obtained also visible spectra in the same observational run. The range from 0.8 to 2.5 mum, encompassing the 1 and 2 mum pyroxene features, allows a precise mineralogical characterization of these asteroids. The obtained data suggests the possible coexistence of distinct mineralogical groups among the V-type asteroids, either probing different layers of (4) Vesta or coming from different bodies. No clear correlation was found between mineralogies and the objects being, or not, member of the Vesta dynamical family. ER - TY - Journal T1 - New Activity of Chiron: Results from 5 Years of Photometric Monitoring A1 - Duffard, René A1 - Lazzaro, Daniela A1 - Pinto, Sandro A1 - Carvano, Jorge A1 - Angeli, Claudia A1 - Alvarez-Candal, Alvaro A1 - Fernández, Silvia JO - Icarus VL - 160 Y1 - 2002/11/1 SP - 44 EP - 51 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Icar..160...44D&db_key=AST&high=42a068d47518458 N2 - The results of photometric observations of Centaur object Chiron carried out at the Observatório do Pico dos Dias (OPD, Brazil), the Estación Astrofísica de Bosque Alegre (EABA, Argentina), and Complejo Astronómico El Leoncito (CASLEO, Argentina) from 1997 to 2001 are presented here. The analysis of the photometric data shows that the brightness of Chiron reached a minimum value in 1999 and began increasing again in 2000. The absolute magnitude, H_V, varied from 7.26 in June 1999 to 5.78 in April 2001. The data tend to indicate that Chiron is starting a new outburst of activity which is compatible with a sporadic cometary behavior not related to heliocentric distance. ER - TY - Journal T1 - Optical Polarization Observations of NGC 6231: Evidence for a Past Supernova Fingerprint A1 - Feinstein, Carlos A1 - Martínez, Ruben A1 - Vergne, M. Marcela A1 - Baume, Gustavo A1 - Vázquez, Rubén JO - Astrophysical Journal VL - 598 Y1 - 2003/11/1 SP - 349 EP - 356 KW - ISM: Dust/ Extinction/ Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 6231- Polarization/ ISM: Supernova Remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...598..349F&db_key=AST&high=42a068d47504399 N2 - We present the first linear multicolor polarization observations for a sample of 35 stars in the direction of the Galactic cluster NGC 6231. We have found a complex pattern in the angles of the polarimetric vectors. Near the core of this cluster the structure shows a semicircular pattern that we have interpreted as a reorientation of the dust particles showing the morphology of the magnetic field. We propose that a supernova event occurred some time ago and produced a shock on the local ISM. We discuss in this paper independent confirmations of this event, both from the studies on the diffuse interstellar absorptions and the results of the pre-main-sequence stars. We also show that a supernova is supported by the evolutionary status of the cluster. Based on observations obtained at Complejo Astronómico El Leoncito (CASLEO), operated under agreement between the CONICET and the National Universities of La Plata, Córdoba, and San Juan, Argentina. ER - TY - Journal T1 - Optical polarization observations in the region of Stock 16 A1 - Feinstein, C. A1 - Baume, G. A1 - Vergne, M. M. A1 - Vázquez, R. JO - Astronomy and Astrophysics VL - 409 Y1 - 2003/10/1 SP - 933 EP - 939 KW - open clusters and associations: individual: Stock16 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...409..933F&db_key=AST&high=42a068d47504399 N2 - We present (UBVRI) multicolor linear polarimetric data for 26 of the brightest stars in the area of the open cluster Stock 16 that were considered to study the properties of the ISM (interstellar medium) towards the cluster. Our data yield a mean polarization percentage of P ~ 2.5%, close to the polarization value produced by the ISM with normal efficiency (P_{lambda_max} ~ 5 E_B-V) undergoing a color excess of E_B-V =0.51. The mean angle of the polarization vectors, theta = 74fdg9 , agrees quite well with the expected angle produced by dust particles aligned in the direction of the galactic disk (and the magnetic field) in the region. A study of the extinction suffered by the stars in the zone was also performed combining our new data with previous photometric data. In this sense, our analysis indicates that the visual absorption affecting Stock 16 stars is mainly produced in front of the cluster by a dust cloud at approximately 500 pc from the sun. The large polarization value of the nonmember star, WR 51, confirms its background star nature. Based on observations obtained at Complejo Astronómico El Leoncito (CASLEO), operated under agreement between the CONICET and the National Universities of La Plata, Córdoba, and San Juan, Argentina. Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/409/933 ER - TY - Journal T1 - Filaments and Ionized Gas in the Vicinity of 3C 244.1 A1 - Feinstein, Carlos A1 - Macchetto, F. Duccio A1 - Martel, André R. A1 - Sparks, William B. JO - Astrophysical Journal VL - 565 Y1 - 2002/1/1 SP - 125 EP - 130 KW - Galaxies: Active/ galaxies: individual (3C 244.1)/ Galaxies: Jets UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...565..125F&db_key=AST&high=42a068d47504399 N2 - We present results of Hubble Space Telescope observations of the radio galaxy 3C 244.1. The broadband F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy, and gaseous filaments and blobs surrounding it. In the narrowband ramp filter, dominated by [O III] lambda5007, these filaments are bright and have the same morphology as the broadband images. To the south, the filaments have a cone-shaped structure, and the radio jet is located at the center of this cone. To the north of the galaxy, the structure is found near the nucleus of the galaxy within its elliptical profile. From the photometry, the two brighter structures seem to be extended narrow-line emission regions. A comparison with diagnostic line ratios shows that the observed emission is consistent with interactions between the expanding radio jet and the local denser medium. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. ER - TY - Journal T1 - The Highly Polarized Open Cluster Trumpler 27 A1 - Feinstein, Carlos A1 - Baume, Gustavo A1 - Vazquez, Ruben A1 - Niemela, Virpi A1 - Cerruti, Miguel Angel JO - Astronomical Journal VL - 120 Y1 - 2000/10/1 SP - 1906 EP - 1912 KW - ISM: Dust/ Extinction/ open clusters and associations: individual (Trumpler 27) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....120.1906F&db_key=AST&high=42a068d47504399 N2 - We have carried out multicolor linear polarimetry (UBVRI) of the brightest stars in the area of the open cluster Trumpler 27. Our data show a high level of polarization in the stellar light with a considerable dispersion, from P=4% to P=9.5%. The polarization vectors of the cluster members appear to be aligned. Foreground polarization was estimated from the data of some nonmember objects, for which two different components were resolved: the first one associated with a dust cloud close to the Sun producing P_lambdamax=1.3% and theta=146°, and a second component, the main source of polarization for the cluster members, originating in another dust cloud, which polarizes the light in the direction of theta=29.5d. From a detailed analysis, we found that the two components have associated values E_B-V<0.45 for the first one and E_B-V>0.75 for the other. Due the difference in the orientation of both polarization vectors, almost 90° (180° at the Stokes representation), the first cloud (theta~146°) depolarizes the light strongly polarized by the second one (theta~29.5d). Based on observations obtanined at Complejo Astronómico El Leoncito (CASLEO), operated under agreement between CONICET and the National Universities of La Plata, Córdoba, and San Juan, Argentina. ER - TY - Journal T1 - The Extended Narrow-Line Region of 3C 299 A1 - Feinstein, Carlos A1 - Macchetto, F. Duccio A1 - Martel, André R. A1 - Sparks, William B. A1 - McCarthy, Patrick J. JO - Astrophysical Journal VL - 526 Y1 - 1999/12/1 SP - 623 EP - 630 KW - GALAXIES: ACTIVE/ GALAXIES: INDIVIDUAL (3C 299)/ GALAXIES: JETS/ GALAXIES: STRUCTURE/ RADIO CONTINUUM: GALAXIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...526..623F&db_key=AST&high=42a068d47504399 N2 - We present results of Hubble Space Telescope (HST) observations of the radio galaxy 3C 299. The broadband F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy with a comet-like structure extending to the northeast in the radio jet direction. The [O III] lambda5007 emission-line map shows a biconical structure centered on the nucleus, which overlaps the structure found in the broadband filters. The radio core coincides with the center of the biconical structure and the radio axes are aligned with the direction of the cones. These data show clear evidence of a strong interaction between the radio jet and the northeastern morphology of the galaxy. We show evidence that this northeast region is an extended narrow-line region (ENLR) the line-ratio diagnostics show that models involving gas shocked by the radio jet plus ionization from a precursor H II region-itself produced by the ionizing photons of the postshocked gas on the preshocked gas-provide a good match to the observations. We investigate the spatial behavior of the ionizing parameter U, by determining the [O III]/[O II] line ratio, which is sensitive to the change of the ionization parameter, and we trace its behavior over the ENLR along the radio jet direction. We find that [O III]/[O II] does not follow a simple dilution model, but rather it is approximately constant over a large range of distance from the nucleus, thus requiring a local source of ionization, which seems to be compatible with the shock models driven by the radio jet. ER - TY - Journal T1 - H II Regions in Southern Spiral Galaxies: The H alpha Luminosity Function A1 - Feinstein, C. JO - Astrophysical Journal Supplement Series VL - 112 Y1 - 1997/9/1 SP - 29 KW - GALAXIES: ISM/ GALAXIES: SPIRAL/ ISM: H II REGIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJS..112...29F&db_key=AST&high=42a068d47504399 N2 - By using narrow-band filters to measure the H alpha flux, a catalog of H II regions in several spiral galaxies was made, consisting of the position and flux of the objects. For each galaxy the H alpha luminosity function was derived. From the observed sample, two galaxies were found to have type II luminosity functions. Some simple models were made in order to understand the nature of the luminosity function (both type I and type II). The goal of our work was to simulate how a change of star-forming region, the cluster-mass distribution, or the initial mass function (in an evolutionary environment) can change the shape of the luminosity function. ER - TY - Journal T1 - Optical CCD Observations of Eta Carinae at La Plata Observatory A1 - Fernandez Lajus, E. A1 - Gamen, R. A1 - Schwartz, M. A1 - Salerno, N. A1 - Llinares, C. A1 - Farina, C. A1 - Amorín, R. A1 - Niemela, V. JO - Informational Bulletin on Variable Stars VL - 5477 Y1 - 2003/11/1 SP - 1 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003IBVS.5477....1F&db_key=AST&high=42a068d47508840 N2 - In 2003.5 Eta Carinae was expected to undergo an X-ray eclipse (Damineli et al., 2000). In the framework of an international campaign to obtain multi-wavelength observations of this event, we have obtained optical CCD images of Eta Carinae. Here, we present the B, V, R, I, data of Eta Car obtained before and during the X-ray eclipse. ER - TY - Journal T1 - Automatic Solar Flare Detection Using Neural Network Techniques A1 - Fernandez Borda, Roberto A. A1 - Mininni, Pablo D. A1 - Mandrini, Cristina H. A1 - Gómez, Daniel O. A1 - Bauer, Otto H. A1 - Rovira, Marta G. JO - Solar Physics VL - 206 Y1 - 2002/4/1 SP - 347 EP - 357 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002SoPh..206..347F&db_key=AST&high=42a068d47502277 N2 - We present a new method for automatic detection of flare events from images in the optical range. The method uses neural networks for pattern recognition and is conceived to be applied to full-disk Halphaimages. Images are analyzed in real time, which allows for the design of automatic patrol processes able to detect and record flare events with the best time resolution available without human assistance. We use a neural network consisting of two layers, a hidden layer of nonlinear neurodes and an output layer of one linear neurode. The network was trained using a back-propagation algorithm and a set of full-disk solar images obtained by HASTA (HalphaSolar Telescope for Argentina), which is located at the Estación de Altura Ulrico Cesco of OAFA (Observatorio Astronómico Félix Aguilar), El Leoncito, San Juan, Argentina. This method is appropriate for the detection of solar flares in the complete optical classification, being portable to any Halphainstrument and providing unique criteria for flare detection independent of the observer. ER - TY - Journal T1 - Phase Diagram in Asteroidal Motion A1 - Fernandez, Silvia A1 - López-García, Francisco JO - Earth Moon and Planets VL - 77 Y1 - 1999/1/1 SP - 73 EP - 81 KW - ASTEROIDS/ RESONANCE/ KIRKWOOD GAPS/ CELESTIAL MECHANICS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999EM%26P...77...73F&db_key=AST&high=42a068d47507317 N2 - In order to study the dynamical behaviour of asteroids in commensurability with a planet, we propose a phase diagram obtained by short computer time. We test this numerical procedure by analyzing the behaviour of real and fictitious asteroids in first order commensurabilities with Jupiter. We have also studied the evolution time of the orbital elements and other variables to compare these results with those obtained in the phase diagram. The results obtained with our numerical technique were compared to similar results previously obtained by other authors. ER - TY - Journal T1 - Dynamical behaviour of asteroids in a second order commensurability. A1 - Fernandez, S. A1 - Roig, F. JO - Astronomy and Astrophysics Supplement Series VL - 114 Y1 - 1995/12/1 SP - 325 KW - ASTEROIDS/ CELESTIAL MECHANICS/ METHODS: NUMERICAL/ CHAOS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26AS..114..325F&db_key=AST&high=42a068d47507317 N2 - The outstanding problem in the zone around the 5:3 commensurability with Jupiter, is the evident absence of asteroids. According to the gravitational hypothesis, this is due to the gravitational perturbation of Jupiter on the motion of asteroids in the outer mainbelt. In this paper we study the motion of fictitious asteroids in the 5:3 mean motion commensurability. We present results of an investigation based on numerical integration. We integrated the newtonian equations of motion in order to study the evolution of orbital elements. We obtained that there is a close dependence between the initial eccentricity e_0_ and the behaviour of the asteroids. We concluded that the 5:3 jovian resonance generates an instability zone in the range 3.665A.U.<=a<=3.735A.U. ER - TY - Journal T1 - Sample of minor merger of galaxies: Optical CCD surface photometry and HII region properties A1 - Ferreiro, D. L. A1 - Pastoriza, M. G. JO - Astronomy and Astrophysics VL - 428 Y1 - 2004/12/1 SP - 837 EP - 846 KW - galaxies: photometry/ galaxies: interactions/ galaxies: irregular UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...428..837F&db_key=AST&high=42a068d47507120 N2 - We present the results of the B, V and I photometry of eleven southern minor mergers. The total apparent B magnitude, integrated B-V and V-I colours were measured. We built B, V, and I equivalent profiles for each galaxy and decomposed them into bulge and disk components when possible. From Halpha+N[II] images we have estimated the basic photometric parameters of the HII regions, such as position, size, B-V and V-I colours, Halpha+[NII] luminosity and EW(Halpha+[NII]) equivalent width. Primary components have blue absolute magnitudes in the range -22 < M_B <-18, with a peak at M_B = - 22. The magnitudes of the secondary components are in the range -22 < M_B < -16 with a maximum at M_B = -19. Most pairs have DeltaM_B ~ 2, which means that in luminosity the primary galaxy is on average about 6 times brighter than the secondary. We found a linear correlation between the luminosity ratios of the components and their ratio of major diameters, leading to mass ratios between 0.04 < M_secondary/M_primary < 0.2, suggesting indeed that our sample is formed by minor mergers. On average the galaxies have colours bluer than those of isolated galaxies with the same morphological type. Most of the HII regions and evolved star-forming regions of the sample were formed between 3.6 to 13.7 Myr ago with an average of (6.3±0.7) Myr. The HII region properties, luminosity, sizes and ages are similar in both components. The HII regions have log (Halpha+[NII]) luminosity between 38.6 and 41.7. The HII region luminosity function for the whole sample fits a power law of index alpha = -1.33. The linear correlation between the luminosity L(Halpha+[NII]) and the size of the HII regions has slope of 2.12±0.06. We found that the disk of the primary component is more luminous than those of Lu's sample, while the disk of the secondary is smaller and fainter. A plot of the disk parameters does not change with colour. This indicates that the different stellar populations in the disks were affected in the same way. Tables \ref{Tfilters}, \ref{Tlog} and Figs. \ref{fig1}-\ref{fig11} are only available in electronic form at http://www.edpsciences.org Tables 4-6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/428/837 ER - TY - Journal T1 - A Polarimetric Survey for Dust in 47 Tucanae A1 - Forte, Juan C. A1 - Bassino, Lilia P. A1 - Vega, E. Irene A1 - Pellizza González, Leonardo J. A1 - Cellone, Sergio A. A1 - Méndez, Mariano R. JO - Astronomical Journal VL - 123 Y1 - 2002/6/1 SP - 3263 EP - 3276 KW - ISM: Dust/ Extinction/ globular clusters: individual (NGC 104)/ globular clusters: individual (47 Tucanae)/ UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123.3263F&db_key=AST&high=42a068d47511650 N2 - We present linear polarization measurements in the V band for 77 stars in the field of the globular cluster 47 Tucanae (NGC 104) and for 14 regions free of bright stars, located along an elliptical isophotal contour of the cluster, as well as UBVRI measurements for the cluster nucleus. The observations show variable foreground polarization that, once removed, leaves marginally significant polarization residuals for the nonvariable bright red giants. Although these residuals are small, there is a systematic trend in the sense that the larger ones are seen toward the south of the cluster (in a direction opposite to that of the cluster proper motion). In contrast, most of the variable stars do show significant intrinsic polarization. The behavior of the star-free regions is similar to that of the nonvariable stars and sets an upper limit to the possible existence of a global pattern of scattered (and polarized) intracluster light in the V band. In turn, the multicolor observations of the cluster nucleus cannot be fitted with a Serkowski law and exhibit a polarization excess in both U and B. This polarization could be explained as a combination of the foreground interstellar component and another component arising from dust located in the nucleus and illuminated by a bright blue post-asymptotic giant branch star (at 48" from the cluster center). Inspection of a set of archival Hubble Space Telescope Wide Field Planetary Camera 2 images reveals the presence of a number of dark patches in the innermost regions of the cluster. A prominent patch (some 5"×3" in size) located 12" from the cluster center and with a position angle (north to east) of 120° has a slightly different polarization compared with that of the cluster nucleus and appears to be a good candidate for identification as a dust globule within the cluster. Based on observations made at the Complejo Astronómico El Leoncito, which is operated under agreement between CONICET and the National Universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - The Globular Cluster System of the Low-Luminosity Elliptical Galaxy NGC 1427 A1 - Forte, Juan C. A1 - Geisler, Doug A1 - Ostrov, Pablo G. A1 - Piatti, Andrés E. A1 - Gieren, Wolfgang JO - Astronomical Journal VL - 121 Y1 - 2001/4/1 SP - 1992 EP - 2002 KW - galaxies: individual (NGC 1427)/ Galaxies: Star Clusters UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121.1992F&db_key=AST&high=42a068d47511650 N2 - Washington photometry is presented for a large number of globular cluster candidates associated with the low-luminosity elliptical galaxy NGC 1427 in the Fornax cluster. The survey is mostly complete to T₁=23.5 (V~24.0) and includes an areal coverage of about 216 arcmin², centered near the galaxy. Most previous studies have failed to detect any evidence of multiple globular cluster populations in this low-luminosity elliptical, in sharp contrast to the bimodal globular cluster systems commonly found in giant ellipticals. The lack of multimodal cluster populations has been used as the basis for suggesting that the formation mechanisms for low-luminosity and giant ellipticals are significantly different. Our metallicity-sensitive C-T₁ photometry (the first such study of a low-luminosity elliptical) reveals a definite bimodal cluster population. The red globular cluster population appears strongly centrally concentrated and practically disappears beyond a galactocentric radius of 120". The mean color of these clusters is similar to that of the inner galaxy halo. Blue globulars, on the other hand, exhibit a shallower spatial distribution. These clusters share a small negative C-T₁ color gradient with the galaxy halo, although they are, on average, some 0.3 mag bluer at all galactocentric radii. The overall mean cluster system metallicity is -0.9+/-0.2. The specific globular cluster frequency S_N is 4.5+/-0.8, if a distance modulus (V₀-M_V)=31.0 is adopted. Our results demonstrate that nonunimodal globular cluster populations exist in low-luminosity ellipticals, as well as in giant ellipticals, and thus that the formation mechanisms for these galaxies may share some similarities. ER - TY - Journal T1 - Position-velocity diagrams of ionized gas in the inner regions of disk galaxies A1 - Funes, J. G. A1 - J., S. A1 - Corsini, E. M. A1 - Cappellari, M. A1 - Pizzella, A. A1 - Vega Beltrán, J. C. A1 - Scarlata, C. A1 - Bertola, F. JO - Astronomy and Astrophysics VL - 388 Y1 - 2002/6/1 SP - 50 EP - 67 KW - galaxies: kinematics and dynamics/ galaxies: ISM/ galaxies: spiral/ galaxies: structure/ galaxies: nuclei/ black hole physics UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...388...50F&db_key=AST&high=42a068d47512128 N2 - We use long-slit spectroscopy along the major axis of a sample of 23 nearby disk galaxies to study the kinematic properties of the ionized-gas component in their inner regions. For each galaxy, we derive the position-velocity diagram of the ionized gas from its emission lines. We discuss the variety of shapes observed in such position-velocity diagrams by comparing the gas velocity gradient, velocity dispersion and integrated flux measured in the inner (r =~ +/-1'') and outer regions (r =~ +/-4''). This kind of analysis allows the identification of galaxies which are good candidates to host a circumnuclear Keplerian gaseous disk rotating around a central mass concentration, and to follow up with Hubble Space Telescope observations. Based on observations carried out at European Southern Observatory (ESO N.58, A-0564), at the Multiple Mirror Telescope, which is a joint facility of the Smithsonian Institution and the University of Arizona, and at the Isaac Newton Telescope operated by the Isaac Newton group at the La Palma island at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. ER - TY - Journal T1 - Kinematics of the Ionized Gas in the Inner Regions of Disk Galaxies A1 - Funes, José G. JO - Publications of the Astronomical Society of the Pacific VL - 113 Y1 - 2001/2/1 SP - 257 EP - 257 KW - Galaxies: Kinematics and Dynamics/ Galaxies: Spiral/ Galaxies: Structure UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001PASP..113..257F&db_key=AST&high=42a068d47512128 N2 - Not Available ER - TY - Journal T1 - Galaxy Disks and Disk Galaxies A1 - Funes, José G. A1 - Corsini, Enrico Maria JO - Publications of the Astronomical Society of the Pacific VL - 112 Y1 - 2000/11/1 SP - 1510 EP - 1511 KW - Conference Highlights UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000PASP..112.1510F&db_key=AST&high=42a068d47512128 N2 - Conference was held in Rome, Italy, at the Pontifical Gregorian University on 2000 June 12-16. Proceedings will be edited by J. G. Funes, S.J., and E. M. Corsini and published in the ASP Conference Series. ER - TY - Journal T1 - The orbit of the double-lined Wolf-Rayet binary HDE 318016 (=WR 98) A1 - Gamen, Roberto C. A1 - Niemela, Virpi S. JO - New Astronomy VL - 7 Y1 - 2002/12/1 SP - 511 EP - 520 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002NewA....7..511G&db_key=AST&high=42a068d47513718 N2 - We present the discovery of OB type absorption lines superimposed to the emission line spectrum and the first double-lined orbital elements for the massive Wolf-Rayet binary HDE 318016 (=WR 98), a spectroscopic binary in a circular orbit with a period of 47.825 days. The semiamplitudes of the orbital motion of the emission lines differ from line to line, indicating mass ratios between 1 and 1.7 for M_WR/M_OB. ER - TY - Journal T1 - High-mass binaries in the very young open cluster NGC 6231. Implication for cluster and star formation A1 - García, B. A1 - Mermilliod, J. C. JO - Astronomy and Astrophysics VL - 368 Y1 - 2001/3/1 SP - 122 EP - 136 KW - GALAXIES: OPEN CLUSTERS AND ASSOCIATIONS: NGC 6231/ STARS: BINARIES: SPECTROSCOPIC/ STARS: EARLY-TYPE/ STARS: ROTATION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...368..122G&db_key=AST&high=42a068d47513839 N2 - New radial-velocity observations of 37 O- and B stars in the very young open cluster NGC 6231 confirm the high frequency of short-period spectroscopic binaries on the upper main sequence. Among the 14 O-type stars, covering all luminosity classes from dwarfs to supergiants, 8 are definitively double-lined systems and all periods but one are shorter than 7 days. Several additional binaries have been detected among the early B-type stars. NGC 6231 is an exceptional cluster to constrain the scenarios of cluster- and binary-star formation over a large range of stellar masses. We discuss the evidences, based on NGC 6231 and 21 other clusters, with a total of 120 O-type stars, for a clear dichotomy in the multiplicity rate and structure of very young open clusters containing O-type stars in function of the number of massive stars. However, we cannot answer the question whether the observed characteristics result from the formation processes or from the early dynamical evolution. ER - TY - Journal T1 - Further Study of the High-Velocity Interstellar Medium in the Carina Nebula A1 - García, Beatriz A1 - Walborn, Nolan R. JO - Publications of the Astronomical Society of the Pacific VL - 112 Y1 - 2000/12/1 SP - 1549 EP - 1558 KW - ISM: Lines and Bands/ open clusters and associations: individual (Collinder 228)/ open clusters and associations: individual (Trumpler 16) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000PASP..112.1549G&db_key=AST&high=42a068d47513839 N2 - We present new spectroscopic data for 12 stars in the field of Trumpler 16 and for 18 stars in Collinder 228, to analyze the behavior of the Ca II and Na I interstellar lines and to study the high radial velocity components. The purpose was to provide a finer map of the small angular scale changes in previously observed high-velocity components. We have found three striking new high-velocity profiles in Tr 16 and one probable case in Cr 228. However, the most important result is that as fainter members of the complex are observed, smaller fractions of high-velocity profiles are found, perhaps indicating that such profiles in the earlier spectral type, more massive stars are formed in their near vicinities, in an interaction between their stellar winds and surrounding interstellar material. ER - TY - Journal T1 - Frequency of Binaries in the Open Cluster Trumpler 14 A1 - García, Beatriz A1 - Malaroda, Stella A1 - Levato, Hugo A1 - Morrell, Nidia A1 - Grosso, Mónica JO - Publications of the Astronomical Society of the Pacific VL - 110 Y1 - 1998/1/1 SP - 53 EP - 59 KW - OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: TRUMPLER 14/ BINARIES: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998PASP..110...53G&db_key=AST&high=42a068d47513839 N2 - We present new spectroscopic data for nine objects among the brightest stars in the field of the open cluster Trumpler 14. Radial velocities were measured from around 80 new spectrograms in order to provide more information about the binary nature of these objects. From this material, we conclude that at least two of the stars in the sample are radial-velocity variables, one of them showing double He i features. ER - TY - Journal T1 - Galaxy pairs in the 2dF survey - I. Effects of interactions on star formation in the field A1 - Lambas, Diego G. A1 - Tissera, Patricia B. A1 - Alonso, M. Sol A1 - Coldwell, Georgina JO - Monthly Notices of the Royal Astronomical Society VL - 346 Y1 - 2003/12/1 SP - 1189 EP - 1196 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.346.1189L&db_key=AST&high=42a068d47509661 N2 - We study galaxy pairs (GPs) in the field selected from the 100-K public release of the Two Degree Field (2dF) galaxy redshift survey. Our analysis provides a well-defined sample of 1258 GPs, a large data base suitable for statistical studies of galaxy interactions in the local Universe, z<= 0.1. GPs were selected by radial velocity (DeltaV) and projected separation (r_p) criteria determined by analysing the star-formation activity within neighbours. We have excluded pairs in high-density regions by removing galaxies in groups and clusters. We analyse the star-formation activity in the pairs as a function of both relative projected distance and relative radial velocity. We found power-law relations for the mean star-formation birth parameter and equivalent widths of the galaxies in pairs as a function of r_p and DeltaV. We find that star formation in GPs is significantly enhanced over that of isolated galaxies with similar redshifts in the field for r_p < 25 h^-1 kpc and DeltaV < 100 km s^-1. We detected that, when compared to isolated galaxies of similar luminosity and redshift distribution, the effects of having a companion are more significant on the star-formation activity of bright galaxies in pairs, unless the pairs are formed by similar luminosity galaxies. In this case, the star formation is enhanced in both components. The ratio between the fractions of star-forming galaxies in pairs and in isolation is a useful tool to unveil the effects of having a close companion. We found that about 50 per cent of GPs do not show signs of important star-formation activity (independently of their luminosities), supporting the hypothesis that the internal properties of the galaxies play a crucial role in the triggering of star formation by interactions. ER - TY - Journal T1 - A Search Program for Objects in the Vicinity of the Earth A1 - Hutton, R. Gil JO - Earth Moon and Planets VL - 71 Y1 - 1995/12/1 SP - 207 EP - 210 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995EM%26P...71..207H&db_key=AST&high=42a068d47502997 N2 - Not Available ER - TY - Journal T1 - Pole coordinates of the asteroid 338 Budrosa: implication for the asteroidal family 124 A1 - Hutton, R. Gil A1 - Licandro, J. A1 - Gallardo, T. JO - Planetary and Space Science VL - 43 Y1 - 1995/6/1 SP - 797 EP - 800 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995P%26SS...43..797H&db_key=AST&high=42a068d47502997 N2 - Not Available ER - TY - Journal T1 - Chaotic diffusion of orbits in systems with divided phase space A1 - Giordano, C. M. A1 - Cincotta, P. M. JO - Astronomy and Astrophysics VL - 423 Y1 - 2004/8/1 SP - 745 EP - 753 KW - diffusion/ stellar dynamics/ celestial mechanics UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...423..745G&db_key=AST&high=42a068d47518541 N2 - In this paper we discuss the relevance of diffusive processes in multidimensional Hamiltonian systems. By means of a rather simple model, we present evidence that for moderate-to-strong chaotic systems the stochastic motion remains confined to disjoint domains on the energy surface, at least for mild motion times. We show that only for extremely large timescales and for rather large perturbations, does the chaotic component appear almost fully connected through the relics of the resonance structure. The discussion whether diffusion over the energy surface could actually occur in asteroidal or galaxy dynamics is also included. ER - TY - Journal T1 - Jacobi Dynamics and the N-Body Problem with Variable Masses A1 - Giordano, C. M. A1 - Plastino, A. R. JO - Celestial Mechanics and Dynamical Astronomy VL - 75 Y1 - 1999/1/1 SP - 165 EP - 183 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999CeMDA..75..165G&db_key=AST&high=42a068d47518541 N2 - An appropriate generalization of the Jacobi equation of motion for the polar moment of inertia I is considered in order to study the N-body problem with variable masses. Two coupled ordinary differential equations governing the evolution of I and the total energy E are obtained. A regularization scheme for this system of differential equations is provided. We compute some illustrative numerical examples, and discuss an average method for obtaining approximate analytical solutions to this pair of equations. For a particular law of mass loss we also obtain exact analytical solutions. The application of these ideas to other kind of perturbed gravitational N-body systems involving drag forces or a different type of mass variation is also considered. ER - TY - Journal T1 - Robe's Restricted Three-Body Problem With Drag A1 - Giordano, C. M. A1 - Plastino, A. R. A1 - Plastino, A. JO - Celestial Mechanics and Dynamical Astronomy VL - 66 Y1 - 1997/1/1 SP - 229 EP - 242 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997CeMDA..66..229G&db_key=AST&high=42a068d47518541 N2 - Not Available ER - TY - Journal T1 - NGC 2571: An intermediate-age open cluster with a White Dwarf candidate A1 - Giorgi, E. E. A1 - Vàzquez, R. A. A1 - Baume, G. A1 - Seggewiss, W. A1 - Will, J.-M. JO - Astronomy and Astrophysics VL - 381 Y1 - 2002/1/1 SP - 884 EP - 893 KW - OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 2571/ STARS: LUMINOSITY FUNCTION/ MASS FUNCTION/ H-R DIAGRAMS/ STARS: CHEMICALLY PECULIAR/ STARS: BLUE STRAGGLERS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...381..884G&db_key=AST&high=42a068d47519020 N2 - CCD UBVI imaging photometry was carried out in the field of the open cluster NGC 2571. From the analysis of our data we state the cluster is at a distance of 1380 +/- 130 pc and its age is 50 +/- 10 x 10⁶ yr. The cluster mass function has a slope larger than a typical Salpeter's law. There are two notorious features in NGC 2571: the cluster contains a high proportion of stars located below the reference line that are serious candidates to be metallic line stars (probably Am-Fm), and shows also a sharp gap along its main sequence that cannot be explained by a random process nor by a biased rejection of cluster members. A striking blue object was detected in the cluster field that could be a white dwarf candidate. Based on observations collected at the European Southern Observatory ESO at La Silla, Chile. ER - TY - Journal T1 - CCD UBVI Photometry and Polarimetry in the Open Cluster Trumpler 21 A1 - Giorgi, E. E. A1 - Baume, G. A1 - Vázquez, R. A. A1 - Feinstein, A. JO - Revista Mexicana de Astronomia y Astrofisica VL - 37 Y1 - 2001/4/1 SP - 15 EP - 33 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001RMxAA..37...15G&db_key=AST&high=42a068d47519020 N2 - CCD UBVI photometry was carried out in the field of the open cluster Trumpler 21. Our data locate the cluster at a distance of 1380 pc in a low absorption zone with E(B-V) = 0.25. The age of the cluster is estimated to be 25-30 × 10⁶ yr based on the superposition of isochrones computed with mass loss and overshooting. The cluster mass spectrum has a slope of 1.44 similar to the typical value 1.35 for field stars. UBVRI polarimetry of its brightest members led us to the finding that diffuse interstellar material is responsible for both polarization percentage and its direction. ER - TY - Journal T1 - Recent theoretical results on coronal heating A1 - Gomez, Daniel O. A1 - Dmitruk, Pablo A. A1 - Milano, Leonardo J. JO - Solar Physics VL - 195 Y1 - 2000/8/1 SP - 299 EP - 318 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000SoPh..195..299G&db_key=AST&high=42a068d47521371 N2 - The scenario of magnetohydrodynamic turbulence in connection with coronal active regions has been actively investigated in recent years. According to this viewpoint, a turbulent regime is driven by footpoint motions and the incoming energy is efficiently transferred to small scales due to a direct energy cascade. The development of fine scales to enhance the dissipation of either waves or DC currents is therefore a natural outcome of turbulent models. Numerical integrations of the reduced magnetohydrodynamic equations are performed to simulate the dynamics of coronal loops driven at their bases by footpoint motions. These simulations show that a stationary turbulent regime is reached after a few photospheric times, displaying a broadband power spectrum and a dissipation rate consistent with the energy loss rates of the plasma confined in these loops. Also, the functional dependence of the stationary heating rate with the physical parameters of the problem is obtained, which might be useful for an observational test of this theoretical framework. ER - TY - Journal T1 - A search for shock-excited molecular hydrogen knots in Chamaeleon I very low mass YSOs A1 - Gómez, M. A1 - Persi, P. A1 - Marenzi, A. R. A1 - Roth, M. A1 - Tapia, M. JO - Astronomy and Astrophysics VL - 423 Y1 - 2004/8/1 SP - 629 EP - 641 KW - stars: formation/ stars: low-mass/ brown dwarfs/ ISM: jets and outflows/ ISM: individual objects: Chamaeleon I UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...423..629G&db_key=AST&high=42a068d47522911 N2 - We have obtained narrow-band images of three selected areas of the Chamaeleon I dark cloud which harbor very low mass young stars, centered on the H₂ and Brgamma lines and neighboring continuum as well as on the broad band K_s. One region is located in the northern part of the cloud, roughly coinciding with the densest area. The other two regions are in the southern section of the cloud. Our aim is to search for H₂ outflows associated with these objects. In the northern region, we found seven new H₂ knots, five of which are aligned in the direction of a previously known ¹²CO molecular bipolar outflow. Further evidence that the class I low mass stellar object ISO-ChaI 192 is the driving source of the molecular flow is given by the presence of a 960 AU long elongated structure at 2.2 mum emanating from this star and oriented parallel to the bipolar structure. Another pair of H₂ knots, although lying relatively nearby, is not aligned with the outflow direction. They are located on opposite sides of C1-6, a low mass class II object in the northern part of the Chamaeleon I dark cloud. In contrast, we fail to detect any H₂ emission object brighter than our sensitivity limit (~6 × 10^-32 W/m² Hz arcsec²) in the two southern areas of the cloud that also harbor several very low mass stars, including two transition stellar/sub-stellar objects. This negative result is probably not surprising in view of the extremely low accretion rates measured for brown dwarfs (dot{M} ~ 10^-12 -10^-9 M_âŠ™ yr^-1). Deeper H₂ observations are required to better constraint the outflow event in sub-stellar objects. Based on observations collected at the European Southern Observatory, La Silla, Chile, ESO proposal 71.C-0144 and at Las Campanas Observatory, Chile. ER - TY - Journal T1 - The globular cluster system of NGC 4374 A1 - Gómez, M. A1 - Richtler, T. JO - Astronomy and Astrophysics VL - 415 Y1 - 2004/2/1 SP - 499 EP - 508 KW - galaxies: distances and redshifts/ galaxies: elliptical and lenticular/ cD/ galaxies: individual: NGC 4374/ galaxies: interactions/ galaxies: star clusters UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...415..499G&db_key=AST&high=42a068d47522911 N2 - We study the globular cluster system (GCS) of the giant elliptical NGC 4374 (M 84) in the Virgo cluster using B and R photometry. The colour distribution is bimodal with peaks at B-R=1.11 and B-R=1.36, fitting well to those found in other early-type galaxies. The radial profile of the cluster number density is flatter than the galaxy light. Using the luminosity function we derive a distance modulus of mu=31.61±0.2, which within the uncertainty agrees with the distance from surface brightness fluctuations. Blue and red clusters show similar radial concentrations and azimuthal distributions. The total number of clusters is N=1775±150, which together with our distance modulus leads to a specific frequency of S_N=1.6±0.3. This value is surprisingly low for a giant elliptical, but resembles the case of merger remnants like NGC 1316, where the low specific frequency is probably caused by the luminosity contribution of an intermediate-age population. A further common property is the high rate of type Ia supernovae which also may indicate the existence of a younger population. However, unlike in the case of NGC 1316, one cannot find any further evidence that NGC 4374 indeed hosts younger populations. The low specific frequency would also fit to a S0 galaxy seen face-on. ER - TY - Journal T1 - Jets and Herbig-Haro Objects in the rho Ophiuchi Embedded Cluster A1 - Gómez, M. A1 - Stark, D. P. A1 - Whitney, B. A. A1 - Churchwell, E. JO - Astronomical Journal VL - 126 Y1 - 2003/8/1 SP - 863 EP - 886 KW - ISM: Herbig-Haro Objects/ ISM: Individual: Name: rho Ophiuchi/ ISM: Jets and Outflows/ Stars: Formation/ Stars: Low-Mass/ Brown Dwarfs/ Stars: Pre-Main-Sequence UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....126..863G&db_key=AST&high=42a068d47522911 N2 - We present results from a near-infrared 2.12 mum survey covering a large portion of the rho Ophiuchi cloud (three regions of ~20^'×20^' each, on average) in an effort to improve the detection of embedded molecular hydrogen emission objects in the cloud. We complement these observations with deep optical [S II] images of six areas of 10^'×10^' each. We recovered all previously known optical jets/Herbig-Haro (HH) objects as well as H₂ outflows in the region and report the detection of four new HH objects and 13 near-infrared knots. We provide coordinates and describe the morphology of these knots, several of which are identified as belonging to the same flow on the basis of morphological and proximity arguments. We discuss likely exciting sources. A unique association of the driving star is not always possible, as several young stars lie in close proximity to these knots. Based on observations collected at the European Southern Observatory, Chile [ESO proposal N.65.I-0576(A)], and at the WIYN Observatory. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatory. ER - TY - Journal T1 - Near-Infrared Spectra of Chamaeleon I Stars A1 - Gómez, M. A1 - Mardones, D. JO - Astronomical Journal VL - 125 Y1 - 2003/4/1 SP - 2134 EP - 2155 KW - Stars: Color-Magnitude Diagrams/ ISM: Individual: Name: Chamaeleon I/ Stars: Formation/ Stars: Low-Mass/ Brown Dwarfs/ Stars: Pre-Main-Sequence UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....125.2134G&db_key=AST&high=42a068d47522911 N2 - We present low-resolution (R~500) near-infrared spectra of 46 candidate young stellar objects in the Chamaeleon I star-forming region recently detected in several deep photometric surveys of the cloud. Most of these stars have K<12. In addition, we present spectra of 63 previously known southern hemisphere young stars mainly belonging to the Chamaeleon I and Lupus dark clouds. We describe near-infrared spectroscopic characteristics of these stars and use the water vapor indexes to derive spectral types for the new objects. Photometric data from the literature are used to estimate the bolometric luminosities of all sources. We apply the pre-main-sequence evolutionary tracks and isochrones of D'Antona & Mazzitelli to derive masses and ages. We detect two objects with mass below the H-burning limit among the 46 new candidates. One of these objects (PMK99 IR Cha INa1) is the likely driving source of a bipolar outflow in the northern region of the cloud. Combining our targets with previously known members of the cloud we analyze the mass and age distributions for 145 stars in the Chamaeleon I dark could. The mass histogram rises from about 2.5 up to 0.4 M_solar and then falls off. The median mass is 0.30 M_solar. The current population with masses greater than 0.4 M_solar is essentially complete. The scarcity of very low mass members is interpreted as population bias toward the least massive and fainter objects. If we assume the true Chamaeleon I initial mass function is flat (in logarithmic mass bins) in the interval 0.4-0.04 M_solar as recently found by Comerón et al. in the central 300 arcmin² region, then we estimate that ~100 stars remain to be found in that mass range. The distribution of ages indicates an active star-formation episode within the last ~5×10⁵ yr and a decreasing rate at older ages (a few times 10⁷ yr). Based on observations collected at the European Southern Observatory, Chile, (ESO proposal N.63.I-0269[A]). ER - TY - Journal T1 - Near-infrared spectra of ISO selected Chamaeleon I young stellar objects A1 - Gómez, M. A1 - Persi, P. JO - Astronomy and Astrophysics VL - 389 Y1 - 2002/7/1 SP - 494 EP - 512 KW - techniques: spectroscopic/ stars: formation/ stars: pre-main sequence/ stars: Hertzsprung-Russell (HR) diagram/ stars: low-mass/ brown dwarfs/ infrared: stars UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...389..494G&db_key=AST&high=42a068d47522911 N2 - We present 0.95-2.5 mu m moderate (R ~ 500) resolution spectra of 19 ISOCAM detected sources in the Chamaeleon I dark cloud. Thirteen of these stars are candidate very low mass members of the cloud proposed by Persi et al. (\cite{per00}) on basis of the mid-IR color excess. The sample also includes a bona-fide young brown dwarf (Cha Halpha 1), a transition - stellar/sub-stellar - object (Cha Halpha 2), one previously known T Tauri star (Sz 33) and three ISOCAM sources with no mid-IR excess. The spectra of the mid-IR color excess sources are relatively flat and featureless in this wavelength range. Both atomic and molecular lines (when in absorption) are partially veiled suggesting the presence of continuum emission from circumstellar dust. In addition some of the sources show Paschen and Brackett lines in emission. We apply the 2 mu m water vapor index defined by Wilking et al. (\cite{wil99}) to estimate spectral types. These stars have spectral types M0-8. We use Persi et al.'s stellar luminosity determinations, in combination with D'Antona & Mazzitelli latest pre-main sequence evolutionary tracks, to estimate masses and ages. The ISOCAM detected mid-IR excess sources have sub-solar masses down to the H-burning limit and a median age of few x10⁶ yr, in good agreement with the higher mass members of this cloud. Based on observations collected at the European Southern Observatory, Chile, (ESO proposal N.65.I-0054). ER - TY - Journal T1 - A Near-Infrared Imaging Survey of the Chamaeleon I Dark Cloud A1 - Gómez, Mercedes A1 - Kenyon, Scott J. JO - Astronomical Journal VL - 121 Y1 - 2001/2/1 SP - 974 EP - 983 KW - ISM: Dust/ Extinction/ ISM: Individual: Name: Chamaeleon I/ Stars: Formation/ Stars: Low-Mass/ Brown Dwarfs/ Stars: Pre-Main-Sequence UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121..974G&db_key=AST&high=42a068d47522911 N2 - We describe a near-infrared imaging survey covering ~1 deg² of the Chamaeleon I dark cloud. The survey is complete for K<15.0, H<16.0, and J<16.5, roughly 2 magnitudes more sensitive than previous large-scale surveys. We use the large number of background stars detected to derive an accurate near-infrared extinction law for the cloud and select new candidate members with near-infrared color excesses. We list ~100 candidates of the cloud with K>=12.0, based on their positions in the J-H, H-K color-color diagram. These new stars have low luminosities (K~12-16, H-K>~0.5-1.5) and may have masses close to or even below the hydrogen-burning limit. ER - TY - Journal T1 - Erratum: ``From Head to Sword: The Clustering Properties of Stars in Orion'' [Astron. J. 115, 1524 (1998)] A1 - Gomez, Mercedes A1 - Lada, Charles J. JO - Astronomical Journal VL - 116 Y1 - 1998/9/1 SP - 1508 EP - 1508 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116.1508G&db_key=AST&high=42a068d47522911 N2 - Two mathematical expressions were incorrectly printed on page 1531. The affected section should read as follows: Moreover, Peebles showed that if the volume density of objects is also a power law in form [i.e., eta(r) propto r^-gamma, then the spectral indices of eta(r) and W(theta) are related by the expression gamma = -1/2 B+2. In this interpretation, the steeper the slope (-B), the more centrally condensed is the radial distribution of stars. Moreover, since B < 0 for all the distributions we observed, the radial falloff of stellar volume density (i.e., gamma ~ 2.1-2.3) would be only slightly steeper than that of an isothermal distribution (gamma = 2). ER - TY - Journal T1 - A Survey of Optical Jets and Herbig-Haro Objects in the rho Ophiuchi Cloud Core A1 - Gómez, Mercedes A1 - Whitney, Barbara A. A1 - Wood, Kenneth JO - Astronomical Journal VL - 115 Y1 - 1998/5/1 SP - 2018 EP - 2027 KW - ISM: H II REGIONS/ ISM: INDIVIDUAL: NAME: RHO OPHIUCHI CLOUD/ ISM: JETS AND OUTFLOWS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....115.2018G&db_key=AST&high=42a068d47522911 N2 - We describe a deep narrowband [S ii] imaging survey of ~0.7 deg^2 covering the rho Ophiuchi cloud core (L1688). We detect seven new jet/Herbig-Haro (HH) objects in our survey, of which three are new detections and four confirm candidates from a recent survey by Wilking et al. Together with the five previously known objects, this brings the total to 12 known jet/HH objects in the cloud. In addition to this, we propose six new candidate HH objects. The most likely sources to power the new jet/HH objects appear to be optically visible stars; however, a conclusive association between the HH objects and pre-main-sequence stars is difficult, as several candidate driving sources lie in close vicinity of the new knots. Practically all of the HH objects are located on the perimeter of the cloud. The lack of optical emission toward the center of the cloud and the high spatial concentration of the youngest protostars toward the densest regions strongly suggest that jets inside the cloud are obscured from our view at optical wavelengths. A near-infrared H_2 survey is required to penetrate into the cloud and to study the outflow activity in this extremely active star-forming region. ER - TY - Journal T1 - From Head to Sword: The Clustering Properties of Stars in Orion A1 - Gomez, Mercedes A1 - Lada, Charles J. JO - Astronomical Journal VL - 115 Y1 - 1998/4/1 SP - 1524 EP - 1535 KW - GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NAME: ORION A/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NAME: LAMBDA ORIONIS KW - OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: ORION A/ OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: LAMBDA ORIONIS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....115.1524G&db_key=AST&high=42a068d47522911 N2 - We investigate the structure in the spatial distributions of optically selected samples of young stars in the Head (lambda Orionis) and in the Sword (Orion A) regions of the constellation of Orion with the aid of stellar surface density maps and the two-point angular correlation function. The distributions of young stars in both regions are found to be nonrandom and highly clustered. Stellar surface density maps reveal three distinct clusters in the lambda Ori region. The two-point correlation function displays significant features at angular scales that correspond to the radii and separations of the three clusters identified in the surface density maps. Most young stars in the lambda Ori region (~80%) are presently found within these three clusters, consistent with the idea that the majority of young stars in this region were formed in dense protostellar clusters that have significantly expanded since their formation. Over a scale of ~0.05d-0.5d the correlation function is well described by a single power law that increases smoothly with decreasing angular scale. This suggests that, within the clusters, the stars either are themselves hierarchically clustered or have a volume density distribution that falls steeply with radius. The relative lack of Halpha emission-line stars in the one cluster in this region that contains OB stars suggests a timescale for emission-line activity of less than 4 Myr around late-type stars in the cluster and may indicate that the lifetimes of protoplanetary disks around young stellar objects are reduced in clusters containing O stars. The spatial distribution of young stars in the Orion A region is considerably more complex. The angular correlation function of the OB stars (which are mostly foreground to the Orion A molecular cloud) is very similar to that of the Halpha stars (which are located mostly within the molecular cloud) and significantly different from that of the young stars in the lambda Ori region. This suggests that, although spatially separated, both populations in the Orion A region may have originated from a similar fragmentation process. Stellar surface density maps and modeling of the angular correlation function suggest that somewhat less than half of the OB and Halpha stars in the Orion A cloud are presently within well-defined stellar clusters. Although all the OB stars could have originated in rich clusters, a significant fraction of the Halpha stars appear to have formed outside such clusters in a more spatially dispersed manner. The close similarity of the angular correlation functions of the OB and Halpha stars toward the molecular cloud, in conjunction with the earlier indications of a relatively high star formation rate and high gas pressure in this cloud, is consistent with the idea that older, foreground OB stars triggered the current episode of star formation in the Orion A cloud. One of the OB clusters (Upper Sword) that is foreground to the cloud does not appear to be associated with any of the clusterings of emission-line stars, again suggesting a timescale (<4 Myr) for emission-line activity and disk lifetimes around late-type stars born in OB clusters. ER - TY - Journal T1 - A survey of optical and near-infrared jets in taurus embedded sources. A1 - Gomez, Mercedes A1 - Whitney, Barbara A. A1 - Kenyon, Scott J. JO - Astronomical Journal VL - 114 Y1 - 1997/9/1 SP - 1138 KW - SURVEYS/ INFRARED: STARS/ STARS: PRE-MAIN SEQUENCE/ ISM: JETS AND OUTFLOWS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997AJ....114.1138G&db_key=AST&high=42a068d47522911 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1138G&db_key=AST ER - TY - Journal T1 - The Bipolar Optical Outflow Associated with PV Cephei A1 - Gomez, Mercedes A1 - Kenyon, Scott J. A1 - Whitney, Barbara A. JO - Astronomical Journal VL - 114 Y1 - 1997/7/1 SP - 265 KW - ISM: JETS AND OUTFLOWS/ STARS: INDIVIDUAL: PV CEPHEI/ STARS: PRE-MAIN SEQUENCE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997AJ....114..265G&db_key=AST&high=42a068d47522911 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..265G&db_key=AST ER - TY - Journal T1 - Crustal thinning in the Southwestern Iberia Margin A1 - González, A. A1 - Torné, M. A1 - Córdoba, D. A1 - Vidal, N. A1 - Matias, L. M. A1 - Díaz, J. JO - Geophysical Research Letters VL - 23 Y1 - 1996/1/1 SP - 2477 EP - 2480 KW - Marine Geology and Geophysics: Marine seismics/ Exploration Geophysics: Seismic methods/ Marine Geology and Geophysics: Gravity/ Exploration Geophysics: Data processing UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996GeoRL..23.2477G&db_key=AST&high=42a068d47524183 N2 - The mode of crustal thinning in the southwestern margin of the Iberian Peninsula is investigated along a transect that extends from onshore Iberia to the eastern end of the Horseshoe Abyssal Plain. On onshore areas, the crustal structure has been deduced using wide-angle seismic reflection data, whereas offshore we have used coincident steep and wide-angle reflection data along a NE-SW oriented seismic profile that extends from Cape San Vicente to the Horseshoe Abyssal Plain. In addition, 2D gravity modelling has been performed to validate the crustal structure deduced from seismic data. Our model results reveal that the crust undergoes a strong but continuous thinning from 31 km onshore Iberia to less than 15 km in the Horseshoe Abyssal Plain and that thinning occurs over horizontal distances of about 120 km. ER - TY - Journal T1 - Spectroscopic Binaries and Kinematic Membership in the Open Cluster NGC 3532 A1 - González, Jorge Federico A1 - Lapasset, Emilio JO - Astronomical Journal VL - 123 Y1 - 2002/6/1 SP - 3318 EP - 3324 KW - Stars: Binaries: Spectroscopic/ Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 3532/ Techniques: Radial Velocities UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123.3318G&db_key=AST&high=42a068d47527134 N2 - We report spectroscopic observations for bright stars in the open cluster NGC 3532 up to 1 mag below the turnoff point. We compute radial velocities by cross-correlations and determine spectral types and rotational velocities. Using 21 stars identified as certain members, we derive a mean cluster velocity of +3.4+/-0.3 km s^-1. From radial velocities and angular distances to the cluster center, we compute membership probabilities for all but two stars that are radial velocity variables. Only one out of 34 program stars is a clear kinematic nonmember. Three spectroscopic binaries and three additional possible radial velocity variables are detected among the 23 stars measured more than once. We report the star HD 96609 as a double-lined spectroscopic binary. Using the two-dimensional cross-correlation technique TODCOR developed by Zucker & Mazeh, we derive the radial velocity curves for both components and obtain the orbital parameters with errors of 0.3% and 0.7% for the projected orbital semiaxis and masses, respectively. This system is composed of two main-sequence stars in a circular orbit, with a period of 8.19 days. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the National Universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - Radial Velocities and Kinematic Membership in the Open Cluster NGC 3114 A1 - González, Jorge Federico A1 - Lapasset, Emilio JO - Astronomical Journal VL - 121 Y1 - 2001/5/1 SP - 2657 EP - 2663 KW - Stars: Blue Stragglers/ Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 3114/ Techniques: Radial Velocities UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121.2657G&db_key=AST&high=42a068d47527134 N2 - Echelle spectroscopic observations for 30 bright stars in the field of the sparse open cluster NGC 3114 are presented. The sample includes main-sequence stars, yellow and red giants, and blue straggler candidates. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. The cluster mean velocity is well defined from eight giants and several main-sequence stars whose average is =-3.52+/-0.25 km s^-1. The membership probabilities of the observed stars are computed on the basis of the velocity distributions of the cluster and field stars, and the expected percentage of contamination at each position. We classified 19 cluster members and 10 nonmembers; the remaining star is a known spectroscopic binary for which no membership probability was assigned. Among the members, there is a bright yellow giant, seven red giants, and four blue straggler candidates, although they should be considered as turn-off stars. The location of two of them in the color-magnitude diagram (slightly blueward of the turn-off) can be explained by their low rotational velocities. No velocity variations were detected in the 16 stars measured more than once, which indicates that NGC 3114 possess an abnormally low binary frequency. From spectral types of cluster members, a distance modulus (V-M_v)=9.8+/-0.2 mag and a reddening E(B-V)=0.07+/-0.01 mag are derived. The cluster age is estimated to be 1.6×10⁸ yr. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the National Universities of La Plata, Córdoba and San Juan. ER - TY - Journal T1 - Radial Velocities, Binarity, and Kinematic Membership in the Open Cluster NGC 2516 A1 - González, Jorge Federico A1 - Lapasset, Emilio JO - Astronomical Journal VL - 119 Y1 - 2000/5/1 SP - 2296 EP - 2302 KW - STARS: BINARIES: SPECTROSCOPIC/ STARS: BLUE STRAGGLERS/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC NUMBER: NGC 2516/ TECHNIQUES: RADIAL VELOCITIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....119.2296G&db_key=AST&high=42a068d47527134 N2 - We present echelle spectroscopic observations for 36 bright (V<9.6) stars in the open cluster NGC 2516, including several blue straggler candidates and four red giants. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. From 22 cluster members a mean cluster velocity of +22.0+/-0.2 km s^-1 was derived. Membership probabilities of the observed stars are computed on the basis of their distance to the cluster center and kinematic criteria. We report the discovery of three double-lined spectroscopic binaries and several probable binaries among main-sequence stars. A binary frequency of more than 26% is found among the high-mass main-sequence stars. The blue straggler HD 66341 is a slowly rotating cluster member with constant velocity, while HD 66194 is a fast-rotating Be star with probable variations in radial velocity. Other blue straggler candidates, such as HD 65663, 65950, 66066, and 65987, must be considered turnoff stars. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the national universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - Generalized Nonextensive Thermodynamics Applied to the Cosmic Background Radiation in a Robertson-Walker Universe A1 - Hamity, Victor H. A1 - Barraco, Daniel E. JO - Physical Review Letters VL - 76 Y1 - 1996/6/1 SP - 4664 EP - 4666 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996PhRvL..76.4664H&db_key=AST&high=42a068d47505101 N2 - Statistical mechanics is useful to introduce generalizations of standard thermodynamics through the generalization of the entropy and other state functions. Along these lines the Tsallis nonextensive and the Bergmann group symmetric generalizations have proven to be very useful. We combine both formalisms to describe the nonextensive thermostatistics in a relativistic setting. We obtain the generalized forms of the first and second laws of thermodynamics for reversible processes, and apply the resulting theory to the cosmic blackbody radiation in a Robertson-Walker model of the Universe. We show that the temperature of the cosmic blackbody radiation varies as the inverse of the scale factor of the Universe, and is independent of the degree of nonextensivity. ER - TY - Journal T1 - Statistics of cluster multiplicity and the nature of ultra high energy cosmic ray sources A1 - Harari, Diego A1 - Mollerach, Silvia A1 - Roulet, Esteban JO - Journal of Cosmology and Astro-Particle Physics VL - 05 Y1 - 2004/5/1 SP - 010 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004JCAP...05..010H&db_key=AST&high=42a068d47506508 N2 - We study in detail the properties of clusters of ultra-high energy cosmic ray events, looking in particular to their angular correlation function and the relative frequency of clusters with different multiplicities (e.g. doublets versus triplets or quadruplets), as well as the way in which these quantities should evolve for different ultra-high energy cosmic ray source scenarios as a function of the experimental exposure achieved. We identify some useful tools which can help to characterize the nature of the cosmic ray sources in a more precise way after a modest increase in statistics is achieved in the very near future, even before strong signals from individual sources become eventually observable. ER - TY - Journal T1 - Depolarization of the cosmic microwave background by a primordial magnetic field and its effect upon temperature anisotropy A1 - Harari, Diego D. A1 - Hayward, Justin D. A1 - Zaldarriaga, Matias JO - Physical Review D VL - 55 Y1 - 1997/2/1 SP - 1841 EP - 1850 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997PhRvD..55.1841H&db_key=AST&high=42a068d47506508 N2 - We estimate the depolarizing effect of a primordial magnetic field upon the cosmic microwave background radiation due to differential Faraday rotation across the last scattering surface. The degree of linear polarization of the CMB is significantly reduced at frequencies around and below 30 GHz (B_*/10^-2 G)^1/2, where B_* is the value of the primordial field at recombination. The depolarizing mechanism reduces the damping of anisotropies due to photon diffusion on small angular scales. The l~1000 multipoles of the CMB temperature anisotropy correlation function in a standard cold dark matter cosmology increase by up to 7.5% at frequencies where depolarization is significant. ER - TY - Journal T1 - UBV photometric study and basic parameters of the southern open cluster NGC 2539 A1 - Lapasset, E. A1 - Clariá, J. J. A1 - Mermilliod, J.-C. JO - Astronomy and Astrophysics VL - 361 Y1 - 2000/9/1 SP - 945 EP - 951 KW - GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 2539/ STARS: HERTZSPRUNG-RUSSEL (HR) AND C-M DIAGRAMS/ METHODS: OBSERVATIONAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...361..945L&db_key=AST&high=42a068d47507230 N2 - We present UBV photoelectric observations of 345 stars in the field of the southern open cluster NGC 2539. The analysis of these data allows to determine that 169 stars are probable members of the cluster main sequence, while 23 are possible members. The CC and CM diagrams reveal a well-defined main sequence and a populous red giant branch. We derive a reddening E(B-V) = 0.06 and an apparent distance modulus V-M_v = 10.60, equivalent to a distance of 1210 pc. The age, determined by fitting isochrones computed by the Geneva group with mass loss and moderate core overshooting, turns out to be 630 Myr, which places this cluster within the Hyades-age group. The isochrone for log t = 8.80 reproduces well the morphology of the upper main sequence band in the two CM diagrams, including the binary ridge. Although this isochrone also reproduces well the general shape of the observed red giant pattern, it appears to be a little too bright and too red. This fact could be probably due to the uncertainty on the exact value of the mixing-length parameter. However, mass loss during the evolution of the red giants might also partially account for their location in the HR diagram. The low contamination of the upper main sequence of the cluster CM diagrams and its populated red giant branch makes NGC 2539 a very good target for testing of theoretical models. Based on observations made at Las Campanas Observatory (Chile) and at European Southern Observatory, La Silla (Chile). Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - Discovery of an eclipsing blue straggler in NGC 2354. A1 - Lapasset, E. A1 - Ahumada, J. JO - Astronomy and Astrophysics VL - 314 Y1 - 1996/10/1 SP - 448 EP - 452 KW - STARS: BINARIES: CLOSE/ STARS: BINARIES: ECLIPSING/ STARS: BLUE STRAGGLERS/ STARS: EVOLUTION/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 2354 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...314..448L&db_key=AST&high=42a068d47507230 N2 - A photometric search for variable stars among the blue stragglers (BS) in southern open clusters of old and intermediate age led to the discovery of one eclipsing binary BS in NGC 2354. The star D266 is 1.5 magnitudes brighter than the cluster turn-off while its angular distance to the cluster center is about seven tenths of the estimated cluster radius. This star was observed for several nights and a total of 422 UBV measurements were obtained. The coverage of the orbital cycle was almost completed, a period of 0.6388228 days was determined, and finally the first light curves of this eclipsing variable star were obtained. They show the typical characteristics of an EB-class close binary with minima about 0.4 and 0.1 magnitudes deep. The photometric analysis by means of the Wilson-Devinney code allowed to define a set of ten possible solutions for assumed values of the mass-ratio between 0.2 and 5.0. Two minima of the quality-of-fit function for q=0.30 and q=3.0 indicate the best solutions we could obtain. Regardless of the value of q, the following features could be established: a) both components are very close to the critical contact lobes and both detached or semidetached configurations fit the light curves in an acceptable way; b) the temperature difference between the components is one of the highest among this type of stars; c) the primary component always remains in the BS zone of the cluster colour-magnitude diagram. If we assume that D266 is a member of NGC 2354, we may conclude that mass-exchange between the components of this system is the most probable cause of its present BS state. ER - TY - Journal T1 - Photometric Analyses of the Short-Period Contact Binaries HY Pavonis, AW Virginis, and BP Velorum A1 - Lapasset, Emilio A1 - Gomez, Mercedes A1 - Farinas, Raul JO - Publications of the Astronomical Society of the Pacific VL - 108 Y1 - 1996/4/1 SP - 332 KW - CATACLYSMIC VARIABLES/ STARS: INDIVIDUAL: HY PAVONIS/ STARS: INDIVIDUAL: AW VIRGINIS/ STARS: INDIVIDUAL: BP VELORUM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996PASP..108..332L&db_key=AST&high=42a068d47507230 N2 - We present BV light curve synthetic analyses of three short period contact (W UMa) binaries: HY Pavonis (P ~0.35 days), AW Virginis (P ~0.35 days), and BP Velorum (P ~0.26 days). Different possible configurations for a wide range of the mass ratio were explored in each case making use of the Wilson-Divinney code. The photometric parameters of the systems were determined from the synthetic light curve solutions that best fit the observations. AW Vir has two components of very similar temperatures and therefore the subtype (A or W) remains undetermined. HY Pav and BP Vel are best modeled by W-type configurations and the asymmetries in the light curves are reproduced by introducing cool spots on the more massive secondary components. Even when BP Vel lies in the region of the open cluster Cr 173, its distance modulus, in principle, rules it out as a cluster member. (SECTION: Stars) ER - TY - Journal T1 - Brane cosmology as a dynamical system A1 - Lara, Luis A1 - Castagnino, Mario JO - Physical Review D VL - 70 Y1 - 2004/8/1 SP - 43535 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004PhRvD..70d3535L&db_key=AST&high=42a068d47512522 N2 - We investigate the qualitative dynamical properties of a brane model for the flat isotropic universe with a single matter component represented by a scalar field. We study the flat and quadratic potential. Three classes of behaviors of the scale factor are determined. In particular, in the case of the brane with dark negative radiation, via a fine tuning, the existence of oscillatory solutions is shown, which is not possible in the traditional flat FRW model. ER - TY - Journal T1 - Infrared mergers and infrared quasi-stellar objects with galactic winds - II. NGC5514: two extranuclear starbursts with LINER properties and a supergiant bubble in the rupture phase A1 - Lípari, S. A1 - Mediavilla, E. A1 - Garcia-Lorenzo, B. A1 - Díaz, R. J. A1 - Acosta-Pulido, J. A1 - Agüero, M. P. A1 - Taniguchi, Y. A1 - Dottori, H. A1 - Terlevich, R. JO - Monthly Notices of the Royal Astronomical Society VL - 355 Y1 - 2004/12/1 SP - 641 EP - 681 KW - ISM: bubbles/ galaxies: individual: NGC5514/ galaxies: interactions/ galaxies: kinematics and dynamics/ quasars: general/ galaxies: starburst UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.355..641L&db_key=AST&high=42a068d47518014 N2 - A study of the morphology, kinematics and ionization structure of the infrared (IR) merger NGC5514 is presented. This study is based mainly on INTEGRAL two-dimensional (2D) spectroscopy (obtained at the 4.2-m William Herschel Telescope, WHT), plus optical and near-IR images. Clear evidence of two extranuclear starbursts with young outflows (OFs) and low-ionization nuclear emission region (LINER) activity are reported. One of these OFs has generated a supergiant bubble and the other is associated with an extended complex of HII regions. In the galactic bubble it was found that: (i) the [SII], Halpha, [NII], [OI] and [OIII] emission-line maps show a bubble with a distorted ellipsoidal shape, with major and minor axes of ~6.5 kpc [13.6 arcsec; at position angle (PA) = 120°+/- 10°] and ~4.5 kpc (9.6 arcsec); (ii) these maps depict four main knots, a very strong one and three others more compact and located at the border; (iii) the centre of the bubble is located at ~4.1 kpc (8.5 arcsec) to the west of the main nucleus; (iv) the WHT spectra show, in this area, two strong components: blue and red emission-line systems, probably associated with emission from the near and far side of the external shell, for which the mean OF velocities were measured as V_OFblue= (-320 +/- 20) kms^-1 and V_OFred= (+265 +/- 25) kms^-1 (v) these two components depict LINER properties, probably associated with large-scale OF + shocks; (vi) at the east border, the kinematics of the ionized gas and the [SII] emission-line maps show an extended ejection of 4 kpc aligned with the PA of the major axis; (vii) three other ejections were found, two of them perpendicular to the extended one. Each ejection starts in one of the knots. These results suggest that the bubble is in the rupture phase. For the complex of giant HII regions it was found that: (i) the Halpha, [NII] and [SII] emission-line maps show a compact strong emission area (peaking at ~810 pc ~1.7 arcsec, to the east of the second nucleus) and faint extended emission with an elongated shape, and major and minor axes of ~5.1 kpc (10.8 arcsec; at PA ~20°) and ~2.9 kpc (6.0 arcsec); (ii) inside this complex, the spectra show HII region and transition LINER/HII characteristics; (iii) at the border of this extended HII area the spectra have outflow components and LINER properties. INTEGRAL 2D [NII], Halpha, [SII] and [OIII] velocity fields (VFs) are presented. These VF maps show results consistent with an expansion of the bubble, plus four ejections of ionized gas. The U, B, V, I, J, H and K_S images show a pre-merger morphology, from which faint filaments of emission emerge, centred on the bubble. The ionization structure and the physical conditions were analysed using the following 2D emission-line ratio and width maps: [SII]/Halpha, [NII]/Halpha, [OI]/Halpha, [OIII]/Hbeta and FWHM-[NII]. In the region of the bubble, 100 per cent of the [NII]/Halpha and [SII]/Halpha ratios show very high values (>0.8) consistent with LINER processes associated with high-velocity shocks. These new results support the previous proposition that extreme nuclear and `extranuclear' starbursts with galactic winds + shocks play an important role in the evolution of IR mergers/quasi-stellar objects. ER - TY - Journal T1 - The nearest extreme starburst: bubbles, young star clusters and outflow in the merger NGC 3256 A1 - Lípari, S. L. A1 - Díaz, R. J. A1 - Forte, J. C. A1 - Terlevich, R. A1 - Taniguchi, Y. A1 - Aguero, M. P. A1 - Alonso-Herrero, A. A1 - Mediavilla, E. A1 - Zepf, S. JO - Monthly Notices of the Royal Astronomical Society VL - 354 Y1 - 2004/10/1 SP - L1 EP - L6 KW - supernovae: general/ ISM: bubbles/ galaxies: individual: NGC 3256/ galaxies: interactions/ galaxies: kinematics and dynamics/ galaxies: star clusters UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.354L...1L&db_key=AST&high=42a068d47518014 N2 - We have studied the extreme starburst in the infrared merger NGC 3256. We detect four galactic bubbles (using ESO New Technology Telescope and Hubble Space Telescope WFPC2 Halpha images). These shells would be associated with previous supernova explosions. The first analysis of the spatial distribution of young star cluster candidates shows that more than 90 per cent of them are located in a complex starburst structure, including some of the bubble walls, three nuclei and three blue asymmetrical spiral arms. We have made a kinematic study of the ionized gas in the core of the main optical nucleus, performed with HST STIS spectra. The shape of the rotation curve and the emission-line profile can be explained by the presence in the core of young star clusters with outflow. Any low-luminosity active galactic nucleus associated with this core would have a mass less than 10⁷ M_solar. It is also probable that the compact X-ray and radio emission of ULX(7)N - the source coincident with the main optical nucleus - is the result of a few recent supernova remnants. ER - TY - Journal T1 - Infrared mergers and infrared quasi-stellar objects with galactic winds - I. NGC 2623: nuclear outflow in a proto-elliptical candidate A1 - Lípari, S. A1 - Mediavilla, E. A1 - Díaz, R. J. A1 - García-Lorenzo, B. A1 - Acosta-Pulido, J. A1 - Agüero, M. P. A1 - Terlevich, R. JO - Monthly Notices of the Royal Astronomical Society VL - 348 Y1 - 2004/2/1 SP - 369 EP - 394 KW - ISM: bubbles/ galaxies: individual: NGC 2623/ galaxies: interactions/ galaxies: kinematics and dynamics/ quasars: general/ galaxies: starburst. UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.348..369L&db_key=AST&high=42a068d47518014 N2 - We present the first results of a study of the morphology, kinematics and ionization structure of infrared (IR) mergers/quasi-stellar objects (QSOs) with galactic winds. This study is based mainly on INTEGRAL two-dimensional (2D) fibre spectroscopy [obtained on the 4.2-m William Herschel Telescope (WHT), La Palma] combined with high-resolution Hubble Space Telescope (HST) observations. Clear evidence of outflow (OF) from the nucleus of the luminous infrared merger NGC 2623 is reported. Specifically: (i) the INTEGRAL 2D Halpha, [N II] and [S II] emission line maps depict a cone-shaped extended nebula that emerges from the nucleus, with an aperture angle theta= 100°+/- 5° and reaching a distance of ~3.2 kpc from the nucleus; (ii) inside the nebula and in the central region, all the emission-line WHT spectra show low velocity blue/OF components, with OF>= (-405 +/- 35) km s^-1 and (iii) in the OF nebula, the emission line ratios are consistent with ionization by a dusty nuclear starburst plus shock heating. These results are consistent with a galactic wind process powered mainly by a nuclear starburst. The INTEGRAL 2D Halpha and [N II]lambda6583 velocity field (VF) maps for the main body of NGC 2623 (16.4 × 12.3 arcsec²; ~5.9 × 4.4 kpc²) show outflow motion in the nuclear and the Halpha+[N II] nebular regions superposed on a general circular motion. This circular motion prevails inside r~ 1.5 kpc, and for larger radii we detected non-circular motions. In the central region, the average observed rotation curve was fitted with a model corresponding to a single-component Plummer spherical potential. After the subtraction of the Plummer and an axisymmetric polynomial model, the residues of the VF in both cases indicate ejection as the origin of the cone nebula. The fitted Plummer model implies a total mass of M_T= 1.5 × 10¹⁰ M_solar and a spherical distribution of matter in the central region. The high-resolution HST WFPC2 F555W (~V) and F814W (~I) broad-band images display a strongly obscured nucleus in the apex of a small nuclear cone, an asymmetrical clumpy spiral arm located to the east of the nucleus, a ring plus an arc to the west and several large-scale filaments of dust. A good r^1/4-law fit to the HST WFPC2 I band luminosity profile was found. In 85 per cent of the INTEGRAL 2D field we measure very high values (>1) of the [N II]lambda6583/Halpha and [S II]lambda6717 + 31/Halpha ratios, suggesting that shocks are important on large scales (in almost all the main body). Furthermore, the 2D full width at half maximum FWHM-[N II] and VF residual maps show a good spatial correlation, suggesting that the OF shocks ionize the gas and broaden the emission lines. However, close to the nucleus, the OF nebula shows low values of the [N II]lambda6583/Halpha ratio (in the range 0.1-0.4), indicating that photoionization by a dusty nuclear starburst also plays a significant role in the excitation of the nebula. The characteristics of the nucleus of NGC 2623 could be associated with a starburst-related LINER. The properties found in IR mergers/QSOs with galactic winds mainly underline the importance of studying the possible link between IR mergers with starburst + galactic wind -> IR QSOs with composite nature + galactic wind, and elliptical galaxies. ER - TY - Journal T1 - Extreme galactic wind and Wolf-Rayet features in infrared mergers and infrared quasi-stellar objects A1 - Lípari, S. A1 - Terlevich, R. A1 - Díaz, R. J. A1 - Taniguchi, Y. A1 - Zheng, W. A1 - Tsvetanov, Z. A1 - Carranza, G. A1 - Dottori, H. JO - Monthly Notices of the Royal Astronomical Society VL - 340 Y1 - 2003/3/1 SP - 289 EP - 303 KW - ISM: bubbles/ galaxies: interactions/ quasars: general/ galaxies: starburst/ infrared: galaxies UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.340..289L&db_key=AST&high=42a068d47518014 N2 - We report, as a part of a long-term study of infrared (IR) mergers and IR quasi-stellar objects (QSOs), detailed spectroscopic evidence for outflow (OF) and Wolf-Rayet (WR) features in the nearby mergers NGC4038/39 and IRAS 23128-5919 (with low-velocity OF); and the nearby QSOs IRAS 01003-2238 and 13218+0552 (with extreme velocity OF, EVOF). We also study the presence of EVOF in a complete sample of ultraluminous IR galaxies and QSOs (`The IRAS 1-Jy Survey', 118 objects). We found EVOF in IRAS 11119+3257, 14394+5332, 15130-1958 and 15462-0450. The low-velocity OF components were detected mainly in objects with starburst processes, i.e. OF associated with galactic winds generated in multiple type II supernova (SN) explosions and massive stars. Meanwhile the EVOF were detected mainly in objects with strong starburst plus obscured IR QSOs; which suggests that the coexistence of both processes could generate EVOF. Hubble Space Telescope (HST) images of IR+BAL+FeII QSOs show in practically all of these objects `arc or shell' features probably associated with galactic winds [i.e. with multiple type II SN explosions or with starburst+active galactic nuclei (AGN)] or merger processes. In addition, we analyse the presence of Wolf-Rayet features in part of the large sample of bright PG-QSOs. We found possible WR features in the FeII PG-QSOs PG1244+026, 1444+407, 1448+273 and 1535+547. The results are discussed mainly within the framework of the composite scenario: starburst+AGN. We analyse the presence of extreme starburst and galactic winds as a possible link between IR mergers and IR QSOs. Finally, we discuss the probable role of mergers, extreme starburst and galactic winds processes in BAL-QSOs and galaxies in formation. ER - TY - Journal T1 - Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256 A1 - Lípari, S. A1 - Díaz, R. A1 - Taniguchi, Y. A1 - Terlevich, R. A1 - Dottori, H. A1 - Carranza, G. JO - Astronomical Journal VL - 120 Y1 - 2000/8/1 SP - 645 EP - 669 KW - Galaxies: Evolution/ Galaxies: Individual: NGC Number: NGC 3256/ Galaxies: Individual: NGC Number: NGC 3256C/ galaxies: individual (NGC 3256A/ NGC 3256B/ NGC 3263)/ Galaxies: Individual: NGC Number: NGC 3262/ Galaxies: Interactions/ Galaxies: Kinematics and Dynamics/ Galaxies: Starburst/ Infrared Radiation/ Galaxies: Quasars: General UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....120..645L&db_key=AST&high=42a068d47518014 N2 - We report detailed evidence for multiple merger, extended massive star formation, galactic wind, and circular/noncircular motions in the luminous infrared galaxy NGC 3256, based on observations of high-resolution imaging (Hubble Space Telescope, ESO NTT), and extensive spectroscopic data (more than 1000 spectra, collected at Estación Astrofísica de Bosque Alegre, Complejo Astronómico el Leoncito, Cerro Tololo InterAmerican Observatory, and IUE observatories). We find in a detailed morphological study (resolution ~15 pc) that the extended massive star formation process detected previously in NGC 3256 shows extended triple asymmetrical spiral arms (r~5 kpc), emanating from three different nuclei. The main optical nucleus shows a small spiral disk (r~500 pc), which is a continuation of the external one and reaches the very nucleus. The core shows blue elongated structure (50 pc×25 pc) and harbors a blue stellar cluster candidate (r~8 pc). We discuss this complex morphology in the framework of an extended massive star formation driven by a multiple merger process (models of Hernquist et al. and Taniguchi et al.). We study the kinematics of this system and present a detailed Halpha velocity field for the central region (40^''×40^'' r_max~30^''~5 kpc), with a spatial resolution of 1" and errors of +/-15 km s^-1. The color and isovelocity maps show mainly (1) a kinematic center of circular motion with ``spider'' shape, located between the main optical nucleus and the close (5") mid-IR nucleus and (2) noncircular motions in the external parts. We obtained three ``sinusoidal rotation curves'' (from the Halpha velocity field) around position angle (P.A.) ~55°, ~90°, and ~130°. In the main optical nucleus we found a clear ``outflow component'' associated with galactic winds plus an ``inflow radial motion.'' The outflow component was also detected in the central and external regions (r<=5-6 kpc). The main axis of the inflow region (P.A.~80^deg) is practically perpendicular to the ouflow axis (at P.A.~160^deg). We analyze in detail the physical conditions in the giant H II regions located in the asymmetric spiral arms, the two main optical nuclei, and the outflow component (using long-slit spectroscopy, plus standard models of photoionization, shocks, and starbursts). We present four detailed emission-line ratios (N II/Halpha, S II/Halpha, S II/S II), and FWHM (Halpha) maps for the central region (30^''×30^'' r_max~22^''~4 kpc), with a spatial resolution of 1". In the central region (r~5-6 kpc) we detected that the nuclear starburst and the extended giant H II regions (in the spiral arms) have very similar properties, i.e., high metallicity and low-ionization spectra, with T_eff=35,000 K, solar abundance, a range of T_e~6000-7000 K, and N_e~100-1000 cm^-3. The nuclear and extended outflow shows properties typical of galactic wind/shocks, associated with the nuclear starburst. We suggest that the interaction between dynamical effects, the galactic wind (outflow), low-energy cosmic rays, and the molecular+ionized gas (probably in the inflow phase) could be the possible mechanism that generate the ``similar extended properties in the massive star formation, at a scale of 5-6 kpc!'' We have also studied the presence of the close merger/interacting systems NGC 3256C (at ~150 kpc, DeltaV=-100 km s^-1) and the possible association between the NGC 3256 and 3263 groups of galaxies. In conclusion, these results suggest that NGC 3256 is the product of a multiple merger, which generated an extended massive star formation process with an associated galactic wind plus a nuclear inflow. Therefore, NGC 3256 is another example in which the relation between mergers and extreme starburst (and the powerful galactic wind, ``multiple'' Type II supernova explosions) play an important role in the evolution of galaxies (the hypothesis of Rieke et al., Joseph et al., Terlevich et al., Heckman et al., and Lípari et al.). Based on observations obtained at the Hubble Space Telescope (HST; Wide Field Planetary Camera 2 [WFPC2] and NICMOS) satellite; International Ultraviolet Explorer (IUE) satellite; European Southern Observatory (ESO, NTT); Chile, Cerro Tololo Inter-American Observatory (CTIO), Chile; Complejo Astronómico el Leoncito (CASLEO), Argentina; Estación Astrofísica de Bosque Alegre (BALEGRE), Argentina. ER - TY - Journal T1 - Luminous Infrared Galaxies. II. NGC 4945: A Nearby Obscured Starburst/Seyfert Nucleus A1 - Lipari, Sebastian A1 - Tsvetanov, Zlatan A1 - Macchetto, F. JO - Astrophysical Journal Supplement Series VL - 111 Y1 - 1997/8/1 SP - 369 KW - GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4945/ GALAXIES: KINEMATICS AND DYNAMICS/ GALAXIES: NUCLEI/ GALAXIES: SEYFERT/ GALAXIES: STRUCTURE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJS..111..369L&db_key=AST&high=42a068d47518014 N2 - We have studied the physical conditions, reddening, and kinematics in the nuclear and circumnuclear regions of the luminous IR source NGC 4945. The I-band image shows a wide cone of radiation that emerges from the partially obscured nuclear region. The H alpha + [N II] image reveals an extended nuclear region located at the same position as the I-band nucleus. Two extended filaments emerge from this region as well. Aperture optical spectroscopy of the nuclear region shows strong reddening in the continuum, and only the blends H alpha + [N II] and [S II] appear in emission. The long-slit spectroscopy at P.A. = 90 deg, coincident with the main H alpha filament, shows in the nuclear region a weak [O I] LINER or weak [O III] Seyfert spectrum and blueshifted broad components in the [N II] and [S II] lines that are probably associated with superwinds. The velocity curve (at P.A. = 90 deg) is clearly asymmetric, with the mean velocity shifted toward the obscured nuclear region. ER - TY - Journal T1 - Astrometry with Virtual Observatories A1 - López, Carlos E. JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 439 EP - 447 KW - astrometry/ databases/ new techniques UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..439L&db_key=AST&high=42a068d47521753 N2 - With the advent of virtual observatories, most astrometry-oriented projects being currently developed---and those to come in the near future---will be greatly enriched. Among these projects it is worth mentioning double stars and multiple systems, proper-motion detections, identification of lost high-proper-motion stars, a detailed census of open cluster members, and precovery of natural satellites, minor planets and comets. A brief discussion of some of these studies is presented. To accomplish the goals proposed by the virtual observatories concept, a massive amount of high-quality astrometric data is needed in advance. It is shown that today's astrometry is about to ready to face these new challenges. ER - TY - Journal T1 - Magnetic twist and writhe of active regions. On the origin of deformed flux tubes A1 - López Fuentes, M. C. A1 - Démoulin, P. A1 - Mandrini, C. H. A1 - Pevtsov, A. A. A1 - van Driel-Gesztelyi, L. JO - Astronomy and Astrophysics VL - 397 Y1 - 2003/1/1 SP - 305 EP - 318 KW - magnetic fields/ methods: data analysis/ Sun: interior/ Sun: magnetic fields/ Sun: photosphere UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...397..305L&db_key=AST&high=42a068d47519327 N2 - We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows. ER - TY - Journal T1 - The Counterkink Rotation of a Non-Hale Active Region A1 - López Fuentes, M. C. A1 - Demoulin, P. A1 - Mandrini, C. H. A1 - van Driel-Gesztelyi, L. JO - Astrophysical Journal VL - 544 Y1 - 2000/11/1 SP - 540 EP - 549 KW - Sun: Activity/ Sun: Corona/ Sun: Interior/ Sun: Magnetic Fields UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...544..540L&db_key=AST&high=42a068d47519327 N2 - We describe the long-term evolution of a bipolar non-Hale active region that was observed from 1995 October to 1996 January. During these four solar rotations the sunspots and subsequent flux concentrations, during the decay phase of the region, were observed to move in such a way that by December their orientation conformed to the Hale-Nicholson polarity law. The sigmoidal shape of the observed soft X-ray coronal loops allows us to determine the sense of the twist in the magnetic configuration. This sense is confirmed by extrapolating the observed photospheric magnetic field, using a linear force-free approach, and comparing the shape of computed field lines with the observed coronal loops. This sense of twist agrees with that of the dominant helicity in the solar hemisphere where the region lies, as well as with the evolution observed in the longitudinal magnetogram during the first rotation. At first sight the relative motions of the spots may be misinterpreted as the rising of an Omega loop deformed by a kink instability, but we deduce from the sense of their relative displacements a handedness for the flux-tube axis (writhe) that is opposite to that of the twist in the coronal loops and, therefore, to what is expected for a kink-unstable flux tube. After excluding the kink instability, we interpret our observations in terms of a magnetic flux tube deformed by external motions while rising through the convective zone. We compare our results with those of other related studies, and we discuss, in particular, whether the kink instability is relevant to explain the peculiar evolution of some active regions. ER - TY - Journal T1 - Preface A1 - Machado, Marcos E. JO - Advances in Space Research VL - 34 Y1 - 2004/1/1 SP - 2169 EP - 2169 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..34.2169M&db_key=AST&high=42a068d47528440 N2 - Not Available ER - TY - Journal T1 - Use of RHESSI observations to determine the origin and fate of non-thermal flare electrons A1 - Machado, Marcos E. A1 - Mandrini, Cristina H. JO - Advances in Space Research VL - 34 Y1 - 2004/1/1 SP - 451 EP - 455 KW - Solar flares/ Hard X-rays/ Particle acceleration UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..34..451M&db_key=AST&high=42a068d47528440 N2 - Most analyses of the characteristics of hard X-ray emission from solar flares have relied on observations of the spectral, temporal and spatial intensity distribution obtained by different instruments and, in the majority of cases, different events. The Reuven Ramaty High Energy Spectroscopic Imager gives us the possibility of combining all three fundamental parameters in a single set of observations from the same instrument. In this paper, we describe a method to compute the distribution of hard X-ray emission in flare loops, which can be used to determine the characteristics of electron energization, transport and thermalization during short lived impulsive peaks. ER - TY - Journal T1 - Astronomy from small earth observation spacecraft A1 - Machado, Marcos E. A1 - Caruso, Daniel JO - Advances in Space Research VL - 31 Y1 - 2003/1/1 SP - 299 EP - 306 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AdSpR..31..299M&db_key=AST&high=42a068d47528440 N2 - Many countries with incipient space activities, such as the case of the authors', dedicate most of their resources to the building of remote sensing applications satellites. In this article we demonstrate that pure scientific research, such as astronomical and solar observing missions, can be carried out in conjunction with the remote sensing missions, provided some versatility in the spacecraft design. ER - TY - Journal T1 - Concepts in Space Science Edited by R.R. Daniel Universities Press (India) Private Limited Distributed by Orient Longman Private Limited ISBN 81 7371 410 X Price: Indian Rs 325; 35.95 plus 15.00 (US$) for packing, handling and shipping by air. (Note: the Service fee per book is lower for shipment of several issues) A1 - Machado, Marcos E. JO - Advances in Space Research VL - 30 Y1 - 2002/1/1 SP - 2157 EP - 2158 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AdSpR..30.2157M&db_key=AST&high=42a068d47528440 N2 - Not Available ER - TY - Journal T1 - Bibliographic catalogue of stellar radial velocities: (1991-1994) A1 - Malaroda, S. A1 - Levato, H. A1 - Morrell, N. A1 - García, B. A1 - Grosso, M. A1 - Bolzicco, G. J. JO - Astronomy and Astrophysics Supplement Series VL - 144 Y1 - 2000/5/1 SP - 1 EP - 4 KW - CATALOGUES/ STARS: KINEMATICS/ TECHNIQUES: RADIAL VELOCITIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26AS..144....1M&db_key=AST&high=42a068d47527954 N2 - We present a bibliographic catalogue of stellar radial velocities with 13359 entries for stars in the galaxy and the Magellanic Clouds, obtained from the issues of several journals published in the period 1991-1994. We have tried to follow the structure of previous compilations although we have relied on data retrived from the SIMBAD database. Catalogue available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - The role of magnetic bald patches in surges and arch filament systems A1 - Mandrini, C. H. A1 - Démoulin, P. A1 - Schmieder, B. A1 - Deng, Y. Y. A1 - Rudawy, P. JO - Astronomy and Astrophysics VL - 391 Y1 - 2002/8/1 SP - 317 EP - 329 KW - magnetohydrodynamics (MHD)/ methods: miscellaneous/ Sun: activity/ Sun: chromosphere/ Sun: magnetic fields UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...391..317M&db_key=AST&high=42a068d47504637 N2 - The short-lived active region (AR) NOAA 7968 was thoroughly observed all along its disk transit (June 3 to 10, 1996) from space and from the ground. During the early stage of its evolution, flux emerged in between the two main polarities and arch filament systems (AFS) were observed to be linked to this emergence. New bipoles and a related surge were observed on June 9. We have modeled the magnetic configuration of AR 7968 using a magnetohydrostatic approach and we have analyzed its topology on June 6 and June 9 in detail. We have found that some of the AFS and the surge were associated with field lines having dips tangent to the photosphere (the so called ``bald patches'', BPs). Two interacting BP separatrices, defining a separator, have been identified in the configuration where these very different events occurred. The observed evolution of the AFS and the surge is consistent with the expected results of magnetic reconnection occuring in this magnetic topology, which is specific to 3D configurations. Previously BPs have been found to be related to filament feet, small flares and transition region brightenings. Our results are evidence of the importance of BPs in a much wider range of phenomena, and show that current layers can be formed and efficiently dissipated in the chromosphere. ER - TY - Journal T1 - Magnetic Field and Plasma Scaling Laws: Their Implications for Coronal Heating Models A1 - Mandrini, C. H. A1 - Démoulin, P. A1 - Klimchuk, J. A. JO - Astrophysical Journal VL - 530 Y1 - 2000/2/1 SP - 999 EP - 1015 KW - SUN: CORONA/ SUN: MAGNETIC FIELDS/ SUN: X-RAYS/ GAMMA RAYS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...530..999M&db_key=AST&high=42a068d47504637 N2 - In order to test different models of coronal heating, we have investigated how the magnetic field strength of coronal flux tubes depends on the end-to-end length of the tube. Using photospheric magnetograms from both observed and idealized active regions, we computed potential, linear force-free, and magnetostatic extrapolation models. For each model, we then determined the average coronal field strength, , in approximately 1000 individual flux tubes with regularly spaced footpoints. Scatter plots of versus length, L, are characterized by a flat section for small L and a steeply declining section for large L. They are well described by a function of the form log=C₁+C₂logL+C₃/2log(L²+S²), where C₂~0, -3<=C₃<=-1, and 40<=S<=240 Mm is related to the characteristic size of the active region. There is a tendency for the magnitude of C₃ to decrease as the magnetic complexity of the region increases. The average magnetic energy in a flux tube, 2>, exhibits a similar behavior, with only C₃ being significantly different. For flux tubes of intermediate length, 50<=L<=300 Mm, corresponding to the soft X-ray loops in a study by Klimchuk & Porter (1995), we find a universal scaling law of the form ~L^delta, where delta=-0.88+/-0.3. By combining this with the Klimchuk & Porter result that the heating rate scales as L^-2, we can test different models of coronal heating. We find that models involving the gradual stressing of the magnetic field, by slow footpoint motions, are in generally better agreement with the observational constraints than are wave heating models. We conclude, however, that the theoretical models must be more fully developed and the observational uncertainties must be reduced before any definitive statements about specific heating mechanisms can be made. ER - TY - Journal T1 - Evidence of Magnetic Reconnection from Halpha, Soft X-Ray and Photospheric Magnetic Field Observations A1 - Mandrini, C. H. A1 - Demoulin, P. A1 - Bagala, L. G. A1 - van Driel-Gesztelyi, L. A1 - Henoux, J. C. A1 - Schmieder, B. A1 - Rovira, M. G. JO - Solar Physics VL - 174 Y1 - 1997/8/1 SP - 229 EP - 240 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997SoPh..174..229M&db_key=AST&high=42a068d47504637 N2 - Not Available ER - TY - Journal T1 - 3D Magnetic Reconnection at an X-Ray Bright Point A1 - Mandrini, C. H. A1 - Demoulin, P. A1 - van Driel-Gesztelyi, L. A1 - Schmieder, B. A1 - Cauzzi, G. A1 - Hofmann, A. JO - Solar Physics VL - 168 Y1 - 1996/9/1 SP - 115 EP - 133 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996SoPh..168..115M&db_key=AST&high=42a068d47504637 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996SoPh..168..115M&db_key=AST ER - TY - Journal T1 - Constraints on flare models set by the active region magnetic topology Magnetic topology of AR 6233. A1 - Mandrini, C. H. A1 - Demoulin, P. A1 - Rovira, M. G. A1 - de La Beaujardiere, J.-F. A1 - Henoux, J. C. JO - Astronomy and Astrophysics VL - 303 Y1 - 1995/11/1 SP - 927 KW - MAGNETOHYDRODYNAMICS (MHD)/ SUN: FLARES/ SUN: MAGNETIC FIELDS/ SUN: ACTIVITY UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...303..927M&db_key=AST&high=42a068d47504637 N2 - We present a detailed analysis of the magnetic topology of AR 6233 on two consecutive days (August 28 and 29, 1990) and compare the location of the magnetic separatrices and separators with off-band Halpha observations and other flare manifestations, such as intense nonthermal electron precipitation and high coronal pressure sites, for two flares that occured on these days. Since for one of the days of our analysis we have two magnetograms covering fields of view with different scale lengths, we analyzed the dependence of the topology of the region of interest on the presence of external magnetic field concentrations. We have found that considering these concentrations does not modify the location of separatrices in the region. Because transverse magnetograms indicate that strong magnetic shear is present along the longitudinal inversion line where flare brightenings are located, the observed photospheric magnetic field is modeled in an approach in which a combination of sources with current-free and non current-free magnetic field is used. This model allows us to obtain a better fit between the observed and modeled transverse field, then we find a closer relationship between separatrices and flare features. The results of a current-free and of a linear force-free approach are also shown for comparison. As in other flaring regions studied previously, chromospheric flare brightenings are found on separatrices. The topological structure obtained for these flares is rather complex. We find that the connectivity of field lines may change drastically from one edge of a ribbon to the other. Electron precipitation and high coronal pressure sites, and some photospheric intense currents are also found in the immediate vicinity of separatrices. The early kernels of August 28 flare are found closer to the separatrices of the nonpotential field, while the later are closer to those of the potential field. All these results agree with the hypothesis that magnetic energy is stored in field-aligned currents and released due to magnetic field reconnection, with a noticeable relaxation of the field, either at the separator region or on separatrices. ER - TY - Journal T1 - Radio star catalogue observed in San Juan (RSSJ95) A1 - Manrique, W. T. A1 - Lizhi, Lu. A1 - Perdomo, R. A1 - Podesta, R. C. A1 - Zezhi, Wang JO - Astronomy and Astrophysics Supplement Series VL - 136 Y1 - 1999/4/1 SP - 7 EP - 11 KW - RADIO CONTINUUM: STARS/ ASTROMETRY/ REFERENCE SYSTEM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26AS..136....7M&db_key=AST&high=42a068d47532476 N2 - Using the data observed in San Juan with the photoelectric Astrolabe Mark II of the Beijing Astronomical Observatory from February, 1992 to March, 1997, the radio star catalogue in San Juan(RSSJ95) has been compiled. There are 69 radio stars in this catalogue. The positions of the radio stars are for the epoch of observation and the equinox J2000.0 and a system close to that of the system FK5. The mean precisions are +/-2.2 ms and +/-0.035'' in right ascensions and declinations, respectively. The magnitudes of stars are from 0.9 to 10.7. The declinations are from -2fdg 5 to -60(deg) . The mean epoch is 1995.1. Finally, the comparison results between the Hipparcos catalogue and RSSJ95 are given. ER - TY - Journal T1 - Second San Juan photoelectric astrolabe catalogue A1 - Manrique, W. T. A1 - Lizhi, Lu. A1 - Perdomo, R. A1 - Podesta, R. C. A1 - Zezhi, Wang A1 - Actis, E. L. A1 - Fanmiao, Zeng A1 - Zhifang, Zeng A1 - Alonso, E. A1 - Pacheco, A. M. A1 - Bustos, G. JO - Astronomy and Astrophysics Supplement Series VL - 136 Y1 - 1999/4/1 SP - 1 EP - 5 KW - CATALOGUE/ ASTROMETRY/ REFERENCE SYSTEMS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26AS..136....1M&db_key=AST&high=42a068d47532476 N2 - According to the cooperation between Beijing, San Juan and La Plata Astronomical Observatories, the photoelectric astrolabe Mark II(PAII) of the Beijing Astronomical Observatory was moved and installed at the San Juan Observatory, Argentina in January, 1992 for observations of the catalogue of stars in the southern hemisphere. The first observing period was from Feb. 23, 1992 to Mar. 31, 1997. Using the data observed in San Juan with the instrument during this period, residuals for 11002 stars are reduced from about 405700 observations of stars over 1532 days. The mean precision of the residuals is +/-0.043''. The Second Catalogue of Stars (CPASJ2) has been compiled from double transits at both the eastern and western passages. There are 5241 stars in this catalogue, including 1225 FK5/FK4Supp stars, 794 FK5Ext stars, 1084 SRS stars, 937 CAMC4 stars, 310 GC stars and 891 IMF stars. The mean precisions are +/-3.2ms and +/-0.057'' in right ascension and declination, respectively. The magnitudes of stars are from 2.0 to 11.5. The declinations are from -3(deg) to -60(deg) . The mean epoch is 1994.9. Finally, systematic corrections of(CPASJ2-FK5) are given. The catalogue is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - Catalogue of HI maps of galaxies. II. Analysis of the data A1 - Martin, M. C. JO - Astronomy and Astrophysics Supplement Series VL - 131 Y1 - 1998/7/1 SP - 77 EP - 87 KW - GALAXIES: ISM/ STRUCTURE/ RADIO LINES: GALAXIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..131...77M&db_key=AST&high=42a068d47506013 N2 - We use some of the maps of the catalogue presented in Paper I to provide some evidence for global conditions that must be fulfilled by the galaxies to have extended hydrogen. For this purpose, we tried to find possible connections between the HI gas extension and other properties of the galaxies (morphological type, surface brightness, gas density, etc.). With isophotal hydrogen diameters of a large sample, we could observe that optically smaller galaxies seem to have greater relative HI extensions. By means of the relation with the apparent HI surface density, we found an expression that should provide a rough estimate of the gas extension. With respect to the dependence on morphological type, we could not find any significant correlation either for the real HI surface density or the relative gas extension. Nevertheless, whereas for spiral and irregular galaxies the real HI surface density exhibits a broad range of values, the values are rather lower for elliptical and S0 galaxies. Table 1 is also available in electronic form at the CDS via anonymous ftp 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - Catalogue of HI maps of galaxies. I. A1 - Martin, M. C. JO - Astronomy and Astrophysics Supplement Series VL - 131 Y1 - 1998/7/1 SP - 73 EP - 75 KW - CATALOGS/ GALAXIES: ISM/ FUNDAMENTAL PARAMETERS/ RADIO LINES: GALAXIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..131...73M&db_key=AST&high=42a068d47506013 N2 - A catalogue is presented of galaxies having large-scale observations in the HI line. This catalogue collects from the literature the information that characterizes the observations in the 21-cm line and the way that these data were presented by means of maps, graphics and tables, for showing the distribution and kinematics of the gas. It contains furthermore a measure of the HI extension that is detected at the level of the maximum sensitivity reached in the observations. This catalogue is intended as a guide for references on the HI maps published in the literature from 1953 to 1995 and is the basis for the analysis of the data presented in Paper II. The catalogue is only available in electronic form at the CDS via anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: luminosity and mass statistics A1 - Martínez, H. J. A1 - Zandivarez, A. A1 - Merchán, M. E. A1 - Domínguez, M. J. L. JO - Monthly Notices of the Royal Astronomical Society VL - 337 Y1 - 2002/12/1 SP - 1441 EP - 1449 KW - galaxies: clusters: general/ galaxies: luminosity function/ mass function/ galaxies: statistics UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.337.1441M&db_key=AST&high=42a068d47529002 N2 - Several statistics are applied to groups and galaxies in groups in the 2° Field Galaxy Redshift Survey. First, we estimate the luminosity functions for different subsets of galaxies in groups. The results are well fitted by a Schechter function with parameters M*- 5 log (h) =-19.90 +/- 0.03 and alpha=-1.13 +/- 0.02 for all galaxies in groups, which is quite consistent with the results of Norberg et al. for field galaxies. When considering the four different spectral types defined by Madgwick et al. we find that the characteristic magnitude is typically brighter than in the field. We also observe a steeper value, alpha=-0.76 +/- 0.03, of the faint end slope for low star-forming galaxies when compared with the corresponding field value. This steepening is more conspicuous, alpha=-1.10 +/- 0.06, for those galaxies in more massive groups than that obtained in the lower-mass subset, . Secondly, we compute group total luminosities using the prescriptions of Moore, Frenk & White. We define a flux-limited group sample using a new statistical tool developed by Rauzy. The resulting group sample is used to determine the group luminosity function and we find a good agreement with previous determinations and semi-analytical models. Finally, the group mass function for the flux-limited sample is derived. An excellent agreement is obtained when comparing our determination with analytical predictions over two orders of magnitude in mass. ER - TY - Journal T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: effects of environment on star formation A1 - Martínez, H. J. A1 - Zandivarez, A. A1 - Domínguez, M. A1 - Merchán, M. E. A1 - Lambas, D. G. JO - Monthly Notices of the Royal Astronomical Society VL - 333 Y1 - 2002/6/1 SP - L31 EP - L34 KW - galaxies: clusters: general/ galaxies: fundamental parameters/ galaxies: general/ galaxies: statistics/ galaxies: stellar content UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.333L..31M&db_key=AST&high=42a068d47529002 N2 - We estimate the fraction of star-forming galaxies in a catalogue of groups, constructed from the 2dF Galaxy Redshift Survey by Merchán & Zandivarez. We use the eta spectral type parameter of galaxies and subdivide the sample of galaxies in groups into four types depending on the values of the eta parameter following Madgwick et al. We obtain a strong correlation between the relative fraction of galaxies with high star formation and the parent group virial mass. We find that even in the environment of groups with low virial mass M~10¹³M_solar the star formation of their member galaxies is significantly suppressed. The relation between the fraction of early-type galaxies and the group virial mass obeys a simple power law spanning over three orders of magnitude in virial mass. Our results show quantitatively the way that the presence of galaxies with high star formation rates is inhibited in massive galaxy systems. ER - TY - Journal T1 - Quasar-Galaxy and AGN-Galaxy Cross-Correlations A1 - Martínez, Héctor J. A1 - Merchán, Manuel E. A1 - Valotto, Carlos A. A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 514 Y1 - 1999/4/1 SP - 558 EP - 562 KW - GALAXIES: ACTIVE/ GALAXIES: CLUSTERS: GENERAL/ COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE/ GALAXIES: QUASARS: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...514..558M&db_key=AST&high=42a068d47529002 N2 - We compute quasar-galaxy and AGN-galaxy cross-correlation functions for samples taken from the Véron-Cetty & Véron catalog of quasars and active galaxies, using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The sample of active galaxy targets shows positive correlation at projected separations r_p<6 h^-1 Mpc consistent with the usual power law. On the other hand, we do not find a statistically significant positive quasar-galaxy correlation signal except in the range 3 h^-1 Mpc Resorting Query Results for 2004A&A...419..965M
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1 Â 2004A&A...419..965M
1.000 06/2004 AÂ Â Â Â Â Â EÂ Â FÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â RÂ Â Â Â Â Â Â Â Â Â SÂ Â Â Â Â Â Â Â Â Â Â Â Â Â UÂ Â Â Â Â Â

MartÃnez,Â R.; Vergne,Â M.Â M.; Feinstein,Â C.
Optical polarization observations in Hogg 22 and NGC 6204

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Smithsonian/NASA ADS Homepage | ADS Sitemap | Query Form | Preferences | HELP | FAQ TY - Journal T1 - Building Reliable Models of M Dwarf Chromospheres: The Spectral Diagnostics A1 - Mauas, Pablo J. D. JO - Astrophysical Journal VL - 539 Y1 - 2000/8/1 SP - 858 EP - 864 KW - Stars: Atmospheres/ Stars: Chromospheres/ Stars: Late-Type UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...539..858M&db_key=AST&high=42a068d47504230 N2 - As part of an ongoing project to study how reliable are the chromospheric models constructed semiempirically to fit the chromospheric spectrum of cold stars, in this paper we study how changes in the assumed chromospheric structure of dM and dMe stars affect the emitted spectrum. In this way, we study if a given set of features can wholly determine the atmospheric structure, how large are the indeterminations in the atmospheric parameters deduced, and to what extent the atmospheric model computed can be considered unique. We find that the profiles of the Ca II K line or the Na D lines can be used to determine the structure of the T_min region and that the Halpha profile can provide good information on the structure of the chromosphere. The Lyalpha flux, in turn, can be used to constrain the position of the transition region. ER - TY - Journal T1 - Chromospheric models of dwarf M stars. A1 - Mauas, P. J. D. A1 - Falchi, A. A1 - Pasquini, L. A1 - Pallavicini, R. JO - Astronomy and Astrophysics VL - 326 Y1 - 1997/10/1 SP - 249 EP - 256 KW - STARS: ATMOSPHERES/ STARS: CHROMOSPHERE/ STARS: LATE-TYPE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...326..249M&db_key=AST&high=42a068d47504230 N2 - We present chromospheric models for two dM stars considered as ``basal'' stars due to the low level of chromospheric activity, and compare them with the model for a very active, flare star obtained in a previous paper. These models are not based on a single spectral feature, but on the continuum in a broad wavelength range (3500-9000Å), on many line profiles corresponding to three different atoms (H, Ca, Na), and on the Mg II h and k flux. We show that a marked chromosphere is present even for stars with the lowest levels of activity, and that the active stars have both a chromospheric temperature rise at larger column mass and a higher chromospheric temperature. These characteristics are responsible for the presence of the Balmer lines in emission in the dMe stars. We also show that the additional energy required to transform a dM star into an active star must be deposited in the high chromosphere, just below the transition region. ER - TY - Journal T1 - Fokker-Planck Description of Electron Beams in the Solar Chromosphere A1 - Mauas, Pablo J. D. A1 - Gomez, Daniel O. JO - Astrophysical Journal VL - 483 Y1 - 1997/7/1 SP - 496 KW - ACCELERATION OF PARTICLES/ SUN: CHROMOSPHERE/ SUN: X-RAYS/ GAMMA RAYS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...483..496M&db_key=AST&high=42a068d47504230 N2 - We numerically solve the relativistic Fokker-Planck equation for a beam of accelerated electrons impinging on the solar chromosphere, for several cases relevant to solar flares. We make a detailed comparison between our results and those obtained from the test-particle approach. We find that the inclusion of velocity diffusion changes significantly not only the resulting distribution function but also macroscopic quantities like the energy deposition rate and the hard X-ray emission. We find that the beam energy is deposited in a deeper and much broader region of the atmosphere. Also, our computations predict a harder and larger hard X-ray emission. These results might be relevant to the long-standing controversy between the thermal and the nonthermal models for the X-ray production, as well as to the study of the acceleration mechanisms of electron beams. ER - TY - Journal T1 - Atmospheric models of flare stars: the flaring state of AD Leonis. A1 - Mauas, P. J. D. A1 - Falchi, A. JO - Astronomy and Astrophysics VL - 310 Y1 - 1996/6/1 SP - 245 EP - 258 KW - STARS: CHROMOSPHERE/ STARS: LATE-TYPE/ STARS: FLARE/ STARS: AD LEO UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...310..245M&db_key=AST&high=42a068d47504230 N2 - We compute a set of semi-empirical atmospheric models for a large flare on the dMe star AD Leo, assuming different filling factors. These are the first models computed to match both the continuum observations, and a wide set of chromospheric spectral lines. We found that the models with a filling factor between 1 and 5% give good agreement between the computed and observed spectral features. Since the main differences between the predicted and observed emission are in the continuum above 4500A and in H_alpha_, simultaneous observations in these spectral features are needed to better determine the filling factor, and whether the area coverage of the flare depends on height. ER - TY - Journal T1 - Isotropization of ultra-high energy cosmic ray arrival directions by radio ghosts A1 - Medina-Tanco, G. A1 - Enßlin, T. A. JO - Astroparticle Physics VL - 16 Y1 - 2001/10/1 SP - 47 EP - 66 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001APh....16...47M&db_key=AST&high=42a068d47502866 N2 - The isotropy in the ultra-high energy cosmic ray (UHECR) flux observed by Yakutsk and AGASA experiments, is a very strong constraint to production and propagation models alike. Most of the scenarios proposed in the literature should produce a sizable anisotropy as either extragalactic luminous or dark matter is normally associated with the invoked particle sources. We explore the possibility that the magnetic fields in fossil cocoons of former radio galaxies - so called radio ghosts [Enßlin, Ringberg Workshop on `Diffuse Thermal and Relativistic Plasma in Galaxy Clusters', vol. 271, MPE Report, 1999, p. 275] - are able to scatter UHECR in the intergalactic medium giving rise to the observed isotropy. We show, through numerical simulations, under which conditions this process can be operative and the magnitude of the effect. We further demonstrate, that if radio ghosts mix with the ambient medium, they might be able to produce the observed magnetic fields in clusters of galaxies. In the case of mixing, the UHECR isotropization would be even stronger than in our conservative estimates. ER - TY - Journal T1 - Ultra-High Energy Cosmic Rays: Are They Isotropic? A1 - Medina-Tanco, Gustavo JO - Astrophysical Journal VL - 549 Y1 - 2001/3/1 SP - 711 EP - 715 KW - ISM: Cosmic Rays/ Cosmology: Dark Matter/ Galaxies: Magnetic Fields/ Galaxy: Halo/ ISM: Magnetic Fields/ Cosmology: Large-Scale Structure of Universe UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...549..711M&db_key=AST&high=42a068d47502866 N2 - From the analysis of Akeno Giant Air Shower Array (AGASA) data above 4×10¹⁹ eV, we show that the ultra-high energy cosmic ray flux is neither purely isotropic nor reflects the expected anisotropy from a pure source distribution that maps large-scale structure in the local universe. The arrival distribution seems to be the result of a mixture of fluxes (e.g., dark matter halo plus large-scale structure) or the superposition of direct and diffuse radiation field components, respectively. Another viable option is an arbitrary extragalactic flux reprocessed by a magnetized galactic wind model, as recently proposed in the literature. ER - TY - Journal T1 - Cosmic Magnetic Fields from the Perspective of Ultra-High-Energy Cosmic Rays Propagation A1 - Medina Tanco, Gustavo JO - LNP Vol. 576: Physics and Astrophysics of Ultra-High-Energy Cosmic Rays VL - 576 Y1 - 2001/1/1 SP - 155 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001LNP...576..155M&db_key=AST&high=42a068d47502866 N2 - The Ultra High Energy Cosmic Ray (UHECR) and Gamma Ray Burst (GRB) fields are very similar in many respects. Both have gone through a burst of activity in source modeling, both have a history of "repeaters" and, for both, the discovery of isotropy in arrival directions mean a fundamental change of current views and ideas. As in the case of gamma ray bursts (GRB), one can expect that the next significant step in our understanding of the UHECR problem will come when some source is finally identified as data accumulates from the new large exposure experiments under construction. However, UHECR are most likely charged particles, and so there is probably not such a thing as an easily identifiable optical counterpart, as there turned out to be with GRBs. Intervening galactic and intergalactic magnetic fields can affect propagation at energies of hundreds of EeV in a very significant way. This coupling means that both, cosmic magnetic fields and UHECR will have to be tackled together. UHECR will be, at the same time, the object of study and an invaluable diagnostic tool for magnetic fields inside the 100 Mpc sphere defined by the Greisen-Zatsepin-Kuzmin cut-off. The prospects for the future will be discussed. ER - TY - Journal T1 - Dark matter halos and the anisotropy of ultra-high energy cosmic rays A1 - Medina Tanco, G. A. A1 - Watson, A. A. JO - Astroparticle Physics VL - 12 Y1 - 1999/10/1 SP - 25 EP - 34 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999APh....12...25M&db_key=AST&high=42a068d47502866 N2 - Several explanations for the existence of Ultra-High Energy Cosmic Rays invoke the idea that they originate from the decay of massive particles created in the reheating following inflation. It has been suggested that the decay products can explain the observed isotropic flux of cosmic rays. We have calculated the anisotropy expected for various models of the dark matter distribution and find that at present data are too sparse above 4 x10^19 eV to discriminate between different models. However, we show that with data from three years of operation of the southern section of the Pierre Auger Observatory significant progress in testing the proposals will be made. ER - TY - Journal T1 - The photodisintegration of cosmic ray nuclei by solar photons: the Gerasimova-Zatsepin effect revisited A1 - Medina-Tanco, Gustavo A. A1 - Watson, Alan A. JO - Astroparticle Physics VL - 10 Y1 - 1999/3/1 SP - 157 EP - 164 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999APh....10..157M&db_key=AST&high=42a068d47502866 N2 - The interesting possibility of measuring the masses of high energy cosmic ray particles by observing pairs of extensive air showers arriving at the earth nearly simultaneously was proposed some years ago by Zatsepin (1951) and Gerasimova and Zatsepin (1960). Such showers would be created by the nuclear fragments originating as a result of the photodisintegration of massive nuclei interacting with the solar radiation field. In this paper we revisit this possibility in the context of existing and proposed detectors of high and ultra-high energy cosmic rays considering a simple, yet realistic, model of the interplanetary magnetic field. The possibility of observing the mass fragmentation of cosmic rays directly, however, remains challenging. ER - TY - Journal T1 - The Energy Spectrum Observed by the AGASA Experiment and the Spatial Distribution of the Sources of Ultra-High-Energy Cosmic Rays A1 - Medina-Tanco, Gustavo A. JO - Astrophysical Journal VL - 510 Y1 - 1999/1/1 SP - L91 EP - L94 KW - ISM: COSMIC RAYS/ COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE/ MAGNETIC FIELDS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...510L..91M&db_key=AST&high=42a068d47502866 N2 - Seven and a half years of continuous monitoring of giant air showers triggered by ultra-high-energy cosmic rays have been summarized recently by the AGASA collaboration. The resulting energy spectrum indicates clearly that the cosmic-ray spectrum extends well beyond the Greisen-Zatsepin-Kuzmin (GZK) cutoff at ~5x10^19 eV. Furthermore, despite the small-number statistics involved, some structure in the spectrum may be emerging. Using numerical simulations, it is demonstrated in the present work that these features are consistent with a spatial distribution of sources that follows the distribution of luminous matter in the local universe. Therefore, from this point of view, there is no need for a second high-energy component of cosmic rays dominating the spectrum beyond the GZK cutoff. ER - TY - Journal T1 - The Effect of Highly Structured Cosmic Magnetic Fields on Ultra-High-Energy Cosmic-Ray Propagation A1 - Medina Tanco, Gustavo A. JO - Astrophysical Journal VL - 505 Y1 - 1998/10/1 SP - L79 EP - L82 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...505L..79M&db_key=AST&high=42a068d47502866 N2 - The possibility that the magnetic field is strongly correlated with the large-scale structure of the universe has been considered recently in the literature. In this scenario, the intergalactic magnetic field has a strong (in units of microgauss) regular component spanning tens of megaparsecs but localized in sheets and filaments, while the vast voids in between are almost free of magnetic field. If true, this could have important consequences on the propagation of ultra-high-energy cosmic rays and severely affect our capacity for doing astronomy with charged particles. A quantitative discussion of these effects is given in the present work. ER - TY - Journal T1 - On the Significance of the Observed Clustering of Ultra--High-Energy Cosmic Rays A1 - Medina Tanco, Gustavo A. JO - Astrophysical Journal VL - 495 Y1 - 1998/3/1 SP - L71 KW - ISM: COSMIC RAYS/ COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE/ MAGNETIC FIELDS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...495L..71M&db_key=AST&high=42a068d47502866 N2 - Three pairs of possibly correlated ultra-high-energy cosmic-ray events were reported by Hayashida et al. Three different numerical models are combined to study the propagation of the corresponding particles through both the intergalactic and Galactic magnetic fields. The spatial dependences of fields and galaxies are accounted for. The results suggest that the pairs are chance clusterings. ER - TY - Journal T1 - Deflection of Ultra--High-Energy Cosmic Rays by the Galactic Magnetic Field: From the Sources to the Detector A1 - Medina Tanco, Gustavo A. A1 - de Gouveia dal Pino, Elisabete M. A1 - Horvath, Jorge E. JO - Astrophysical Journal VL - 492 Y1 - 1998/1/1 SP - 200 KW - ISM: COSMIC RAYS/ GALAXY: HALO/ METHODS: NUMERICAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...492..200M&db_key=AST&high=42a068d47502866 N2 - We report the results of three-dimensional simulations of the trajectories of ultra-high-energy (UHE) protons and Fe nuclei (with energies E = 4 x 1019 and 2.5 x 1020 eV), propagating through the Galactic magnetic field (GMF) from the sources to the detector. A uniform distribution of antiparticles is backtracked from the detector, at the Earth, to the halo of the Galaxy. We assume an axisymmetric, large-scale spiral magnetic field that permeates both the disk and the halo. A normal field component to the Galactic plane (Bz) is also included in part of the simulations. We find that the presence of a large-scale GMF does not generally affect the arrival directions of the protons, although the inclusion of a Bz component may cause significant deflection of the lower energy protons (E = 4 x 1019 eV). Error boxes larger than or equal to ~5 deg are most expected in this case. On the other hand, in the case of heavy nuclei, the arrival direction of the particles is strongly dependent on the coordinates of the particle source. The deflection may be high enough (>20 deg) as to make any identification of the sources extremely difficult unless the real magnetic field configuration is determined accurately. Moreover, not every incoming particle direction is allowed between a given source and the detector. This generates sky patches that are virtually unobservable from the Earth. In the particular case of the UHE events of Yakutsk, Fly's Eye, and Akeno, they come from locations for which the deflection caused by the assumed magnetic field is not significant. ER - TY - Journal T1 - Structure, Velocity Field, and Turbulence in NGC 604 A1 - Medina Tanco, G. A. A1 - Sabalisck, N. A1 - Jatenco-Pereira, V. A1 - Opher, R. JO - Astrophysical Journal VL - 487 Y1 - 1997/9/1 SP - 163 KW - GALAXIES: INDIVIDUAL MESSIER NUMBER: M33/ ISM: H II REGIONS/ ISM: INDIVIDUAL NGC NUMBER: NGC 604/ ISM: KINEMATICS AND DYNAMICS/ TURBULENCE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...487..163M&db_key=AST&high=42a068d47502866 N2 - The H alpha peak intensity, velocity shift, and velocity dispersion maps of the giant H II region NGC 604 in M33, obtained by two-dimensional high spatial resolution Fabry-Perot observations at the 4.2 m William Herschel Telescope in Spain, are analyzed via two-point correlation functions. The whole system seems to rotate as a rigid body on scales from 50 to 80 pc (the largest studied scale), with a period of ~85 Myr. We demonstrate that the cloud seems to be comprised of eddies with varying characteristic scale lengths which range from 10 pc to the largest observed scales. The calculated kinetic energy spectrum may be interpreted either as a manifestation of a double cascading spectrum of forced two-dimensional turbulence or as a Kolmogorov three-dimensional turbulence (although this last possibility seems unlikely). According to the first interpretation, turbulence is being forced at scales of ~10 pc, while an enstrophy (mean square vorticity) cascade has developed down to the smallest scales resolved and an inverse kinetic energy cascade extends up to scales of ~70 pc, where a low wavenumber turnover is observed; if this interpretation is correct, this would be the first time that such a phenomenon has been observed outside the solar system. As for the second interpretation, energy should be injected at the largest scales, ~70 pc. In both cases the average intrinsic optical depth consistent with the results is ~20 pc. ER - TY - Journal T1 - Non-diffusive propagation of ultra high energy cosmic rays A1 - Medina Tanco, G. A. A1 - de Gouveia dal Pino, E. M. A1 - Horvath, J. E. JO - Astroparticle Physics VL - 6 Y1 - 1997/3/1 SP - 337 EP - 342 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997APh.....6..337M&db_key=AST&high=42a068d47502866 N2 - We report the results of 3D simulations of non-diffusive propagation of Ultra High Energy Cosmic Rays (UHECR) (E > 10^20 eV) through the intergalactic and extended halo media. We quantify the expected angular and temporal correlations between the events and the sources, and the temporal delay between protons and gamma-ray counterparts with a common origin for both halo and extragalactic origins. It is shown that the proposed UHECR-supergalactic plane source associations require either extremely high values of the halo magnetic field over as much as 100 kpc length scale or a very large correlation length for the IGM, even for the largest possible values of the intergalactic magnetic field. It can be stated that the UHECR seem to point to the sources even more strongly than previously believed. The simulations also show that the calculated time delays between UHE protons and gamma-ray counterparts do not match the claimed GRB-UHECR associations for either cosmological or extended halo distance scales. ER - TY - Journal T1 - The Acceleration and Propagation of Strangelets in the Galaxy: Numerical Simulations A1 - Medina-Tanco, G. A. A1 - Horvath, J. E. JO - Astrophysical Journal VL - 464 Y1 - 1996/6/1 SP - 354 KW - ACCELERATION OF PARTICLES/ ISM: COSMIC RAYS/ ELEMENTARY PARTICLES/ STARS: NEUTRON UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...464..354M&db_key=AST&high=42a068d47502866 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...464..354M&db_key=AST ER - TY - Journal T1 - Spectral classification and HR diagram for symbiotic stars in the galactic bulge A1 - Medina Tanco, G. A. A1 - Steiner, J. E. JO - Astronomical Journal VL - 109 Y1 - 1995/4/1 SP - 1770 EP - 1783 KW - GALACTIC BULGE/ LUMINOSITY/ MILKY WAY GALAXY/ SPECTRUM ANALYSIS/ STELLAR EVOLUTION/ STELLAR MASS/ SYMBIOTIC STARS/ ABSORPTION SPECTRA/ HERTZSPRUNG-RUSSELL DIAGRAM/ METALLICITY/ TELLURIC LINES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995AJ....109.1770M&db_key=AST&high=42a068d47502866 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.1770M&db_key=AST ER - TY - Journal T1 - The edge of the Kuiper belt: the Planet X scenario A1 - Melita, M. D. A1 - Williams, I. P. A1 - Collander-Brown, Simon J. A1 - Fitzsimmons, Alan JO - Icarus VL - 171 Y1 - 2004/10/1 SP - 516 EP - 524 KW - Trans-neptunian objects/ Planetary dynamics/ Orbits/ solar system UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Icar..171..516M&db_key=AST&high=42a068d47505895 N2 - Our goal is to determine whether or not the observed sudden termination of the Edgeworth-Kuiper belt can be the result of perturbations from a hypothetical planet. We investigate the effects that such an object would produce on the primordial orbital distribution if the trans-neptunian objects, for a range of masses and orbital parameters of the hypothetical planet. In this numerical investigation, the motion of the hypothetical planet was influenced by the existing planets but not by its interaction with the disk. We find that no set of parameters produce results that match the observed data. Dynamical interaction with the disk is likely to be important so that the orbit of the hypothetical planet changes significantly during the integration interval. This is also discussed. The overall conclusion is that none of the models for the hypothetical planet that were investigated can reproduce the observed features of the Edgeworth-Kuiper belt starting from any probable primordial distribution. ER - TY - Journal T1 - Planet X and the Extended Scattered Disk A1 - Melita, M. D. A1 - Williams, I. P. JO - Earth Moon and Planets VL - 92 Y1 - 2003/6/1 SP - 447 EP - 452 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003EM%26P...92..447M&db_key=AST&high=42a068d47505895 N2 - The effects that a hypothetical trans-Plutonian planet would produce on the orbital distribution of the Classical Edgeworth-Kuiper-Belt, has been surveyed for different physical and orbital parameters of the hypothetical body in Melita et al. (2003a). The best fits were obtained by a moderately eccentric and inclined Earth-sized object with a semimajor axis of ~ 70 AU. However the history of some objects in the `Extended Scattered disk' still represent a puzzle. One possibility is that they can be `extracted' from the Scattered disk by the planetoid. In this work we confirm that such an hypothesis would not explain the present orbit of 2000 CR105, given the conditions for a gap as observed to be formed in the Classical EKB. ER - TY - Journal T1 - A possible long-lived asteroid population at the equilateral Lagrangian points of Saturn A1 - Melita, M. D. A1 - Brunini, Adrian JO - Monthly Notices of the Royal Astronomical Society VL - 322 Y1 - 2001/4/1 SP - L17 EP - L21 KW - CELESTIAL MECHANICS/ MINOR PLANETS/ ASTEROIDS/ PLANETS AND SATELLITES: FORMATION/ SOLAR SYSTEM: FORMATION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.322L..17M&db_key=AST&high=42a068d47505895 N2 - The Lagrangian equilateral points of a planetary orbit are points of equilibrium that trail at 60°, ahead (L4) or behind (L5), the trajectory of a planet. Jupiter is the only major planet in our Solar system harbouring a known population of asteroids at those locations. Here we report the existence of orbits close to the Lagrangian points of Saturn, stable at time-scales comparable to the age of the Solar system. By scaling with respect to the Trojan population we have estimated the number of objects that would populate the regions, which gives a significant figure. Moreover, mutual physical collisions over the age of the Solar system would be very rare, so the evaporation rate of this swarm arising from mutual interactions would be very low. A population of asteroids not self-collisionally evolved after their formation stage would be the first to be observed in our planetary system. Our present estimations are based on the assumption that the capture efficiency at Saturn's equilateral points is comparable with the one corresponding to Jupiter, thus our figures may be taken as upper limits. In any case, observational constraints on their number would provide fundamental clues to our understanding of the history of the outer Solar system. If they existed, the surface properties and size distribution of those objects would represent unusually valuable fossil records of our early planetary system. ER - TY - Journal T1 - Comparative Study of Mean-Motion Resonances in the Trans-Neptunian Region A1 - Melita, M. D. A1 - Brunini, A. JO - Icarus VL - 147 Y1 - 2000/9/1 SP - 205 EP - 219 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000Icar..147..205M&db_key=AST&high=42a068d47505895 N2 - In this work we are interested in the present dynamical structure of the trans-neptunian region. It is known that at moderate to high eccentricities, stable orbits lie close to an exterior-mean-motion resonance with Neptune (NMMR). We study some NMMRs under different points of view. Intrinsic probabilities of collision and dynamical diffusion time-scales using frequency-map analysis have been computed. We have found that collisions and gravitational encounters by themselves would not produce remarkable differences between the number of objects orbiting in each resonance at present. However, frequency-map analysis reveals a much more robust region at the 2:3 NMMR than at the other NMMRs. Naturally the net orbital effect of the encounters can be enhanced differently in each individual NMMR due to differences in size of the stable niches, allowing the populations in the more unstable regions to evaporate sooner. We also study how certain evolutionary models, related with the orbital expansion of the outer planets during their formation stage, could result in resonant populations with a noticeably different primordial number of members. Finally, our results are discussed with reference to the present observational evidence and to our current understanding of the formation of the outer Solar System. ER - TY - Journal T1 - Planetary commensurabilities driven by accretion and dynamical friction A1 - Melita, M. D. A1 - Woolfson, M. M. JO - Monthly Notices of the Royal Astronomical Society VL - 280 Y1 - 1996/6/1 SP - 854 EP - 862 KW - ACCRETION/ ACCRETION DISCS/ PLANETS AND SATELLITES: GENERAL/ SOLAR SYSTEM: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996MNRAS.280..854M&db_key=AST&high=42a068d47505895 N2 - Numerical integrations of a three-body problem, consisting of the Sun and two planets under the influence of both accretion and dynamical friction forces, evolve into planetary resonance when the inner body is more massive. After a transient, the ratio of the periods oscillates closely about a commensurable value; the semimajor axes of both bodies decay, and the eccentricities, which are initially damped, remain constant after the resonance is established. The inclinations are rapidly damped to the mean plane. Although not all the parameters used in this model represent a strictly realistic situation, this work shows that this mechanism could explain the near- commensurable relations found between the periods of the major planets. ER - TY - Journal T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: the catalogue A1 - Merchán, Manuel A1 - Zandivarez, Ariel JO - Monthly Notices of the Royal Astronomical Society VL - 335 Y1 - 2002/9/1 SP - 216 EP - 222 KW - methods: data analysis/ catalogues/ cosmology: observations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.335..216M&db_key=AST&high=42a068d47506071 N2 - We construct a galaxy groups catalogue from the public 100-K data release of the 2dF Galaxy Redshift Survey. The group identification is carried out using a slightly modified version of the group-finding algorithm developed by Huchra & Geller. Several tests using mock catalogues allow us to find the optimal conditions to increase the reliability of the final group sample. A minimum number of four members, an outer number density enhancement of 80 and a linking radial cut-off of 200 km s^-1 are the best obtained values from the analysis. Using these parameters, approximately 90 per cent of groups identified in real space have a redshift space counterpart. On the other hand, the level of contamination in redshift space reaches 30 per cent, including ~6 per cent of artificial groups and ~24 per cent of groups associated with binaries or triplets in real space. The final sample comprises 2209 galaxy groups covering the sky region described by Colless et al.spanning over the redshift range of 0.003 <=z<= 0.25 with a mean redshift of 0.1. ER - TY - Journal T1 - Correlation Function of Galaxy Groups A1 - Merchán, Manuel E. A1 - Maia, Marcio A. G. A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 545 Y1 - 2000/12/1 SP - 26 EP - 31 KW - Galaxies: Clusters: General/ Galaxies: Statistics/ Cosmology: Large-Scale Structure of Universe UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...545...26M&db_key=AST&high=42a068d47506071 N2 - We use the Updated Zwicky Catalog of galaxies to generate a catalog of groups by means of a friends-of-friends algorithm. The groups identified have four or more members and a surrounding density contrast deltarho/rho=80. They cover the region -4^degdeg, |b|>20^deg spanning the radial velocity range of 2000-1. The total sample (hereafter GUZC) comprises 517 groups. The correlation length of the total sample is well fitted with a power law xi(r)=(r/r₀)^gamma, with parameters r₀=9.0+/-0.4 h^-1 Mpc and gamma=-1.67+/-0.09 for values of r<70 h^-1 Mpc, declining to homogeneity at larger scales. Three subsamples defined by the range of group virial masses M were used to examine their clustering properties throughout the autocorrelation function. We find an increase of the amplitude of the correlation function according to the group masses, which extends the results of the r₀-d_c relation for galaxy systems at small d_c. We obtain r₀=9.5+/-0.5 h^-1 Mpc (gamma=-1.81+/-0.12), r₀=10.8+/-0.7 h^-1 Mpc (gamma=-1.77+/-0.17), and r₀=14.1+/-1.2 h^-1 Mpc (gamma=-1.65+/-0.22) for mass ranges 5×10¹²14 M_solar , 2×10¹³14 M_solar, and 5×10¹³14 M_solar, respectively. For completeness, we have also analyzed a sample of groups obtained from the Southern Sky Redshift Survey in the range of virial masses 5×10¹²14 M_solar to compare the results with those obtained from GUZC. The correlation function of this sample can be fitted with a power law with parameters r₀=8.4+/-1.8 h^-1 Mpc and gamma=-2.0+/-0.7. ER - TY - Journal T1 - Cluster-Galaxy Correlations in Cold Dark Matter Models A1 - Merchan, Manuel E. A1 - Abadi, Mario G. A1 - Lambas, Diego G. A1 - Valotto, Carlos JO - Astrophysical Journal VL - 497 Y1 - 1998/4/1 SP - 32 KW - COSMOLOGY: OBSERVATIONS/ COSMOLOGY: THEORY/ COSMOLOGY: DARK MATTER/ METHODS: NUMERICAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...497...32M&db_key=AST&high=42a068d47506071 N2 - We study the ability of COBE-normalized cold dark matter (CDM) models to reproduce observed properties of the distribution of galaxies and clusters using N-body numerical simulations. We analyze the galaxy-galaxy and cluster-galaxy two-point correlation functions, xi gg and xi cg, in open ( Omega 0 = 0.4, Omega Lamda = 0, sigma 8 = 0.75) and flat ( Omega 0 = 0.3, Omega Lamda = 0.7, sigma 8 = 1.05) CDM models, both of which reproduce the observed abundances of rich clusters of galaxies. To compare models with observations, we compute projected cross-correlation functions omega gg and omega cg to derive the corresponding xi gg and xi cg. We use target galaxies selected from the Las Campanas Redshift Survey, target clusters selected from the APM Cluster Survey, and tracer galaxies from the Edinburgh Durham Sky Survey catalog. We find that the open model is able to reproduce the observed xi gg, whereas the flat model needs antibias in order to fit the observations. Our estimate of xi cg for the APM cluster sample analyzed is consistent with a power law xi cg = (r/r0) gamma with r0 = 10.0 +/- 0.7 h-1 Mpc and gamma ~= -2.1. For the open and flat-antibiased CDM models explored we find the corresponding cluster-galaxy correlation lengths 6.5 +/- 0.7 h-1 Mpc and 7.2 +/- 0.5 h-1 Mpc, respectively, significantly lower than the observed value. Our results indicate that COBE-normalized CDM models are not able to reproduce the spatial cross-correlation of clusters and galaxies. ER - TY - Journal T1 - Ionization and Molecular Formation in a Hydrogen-Deficient Carbon-Rich Mixture A1 - Merlo, David C. A1 - Milone, Luis A. JO - Astrophysics and Space Science VL - 288 Y1 - 2003/1/1 SP - 223 EP - 236 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Ap%26SS.288..223M&db_key=AST&high=42a068d47507523 N2 - In this paper the ionization stage and the relationship connecting electronic pressure, gaseous pressure and temperature are studied in a H-deficient, extreme-He mixture which, also, has an overabundance of C (HdC mixture). For comparison purposes a similar analysis is made for a solar mixture and for a metal-deficient one. In our study we take account of the formation of negative ions and of molecules; the selected physical conditions roughly suit those in stellar atmospheres. The relation log (P_g/P_e) vs. log P_e is examined and their properties are interpreted. It is also shown that for those temperatures and pressures in which the main source of opacity is the Thomson scattering, the HdC mixture is less opaque than the solar one (or the pop. II one). For low temperatures, the low abundance of C will strongly limit the formation of C^- in the HdC mixture, thus preventing it from reaching the absorbing importance of H^- in the solar one. C in the HdC mixture mimics the behavior of H in the solar one: either as an electron donor, as a maker of molecules or as a source of opacity. The similarity is qualitative only. ER - TY - Journal T1 - Stability of rotating spherical stellar systems A1 - Meza, A. JO - Astronomy and Astrophysics VL - 395 Y1 - 2002/11/1 SP - 25 EP - 30 KW - celestial mechanics/ stellar dynamics/ galaxies: kinematics and dynamics/ instabilities/ methods: N-body simulations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...395...25M&db_key=AST&high=42a068d47508761 N2 - The stability of rotating isotropic spherical stellar systems is investigated by using N-body simulations. Four spherical models with realistic density profiles are studied: one of them fits the luminosity profile of globular clusters, while the remaining three models provide good approximations to the surface brightness of elliptical galaxies. The phase-space distribution function f(E) of each one of these non-rotating models satisfies the sufficient condition for stability df/dE<0. Different amounts of rotation are introduced in these models by changing the sign of the z-component of the angular momentum for a given fraction of the particles. Numerical simulations show that all these rotating models are stable to both radial and non-radial perturbations, irrespective of their degree of rotation. These results suggest that rotating isotropic spherical models with realistic density profiles might generally be stable. Furthermore, they show that spherical stellar systems can rotate very rapidly without becoming oblate. ER - TY - Journal T1 - Partition Functions of the Light Elements (H to Na), A Revision A1 - Milone, Luis A. A1 - Merlo, David C. JO - Astrophysics and Space Science VL - 259 Y1 - 1998/1/1 SP - 173 EP - 189 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998Ap%26SS.259..173M&db_key=AST&high=42a068d47510869 N2 - As the extensive calculations of atomic partition functions (APFs) made by Traving, Baschek and Holweger, Irwin, and Sauval and Tatum, have been widely used in the literature, the aim of this paper is to analyze whether the numerical values derived from their approximations are homogeneous and accurate, and which are their limitations. Irwin, and Sauval and Tatum, made their calculations for a lowering of the ionization energy Deltachi =0.1 eV, and within a limited range of temperature; we found here, that in the solar atmosphere 0.005 <= Deltachi <= 0.154 eV for a neutral atom (0.008 <= Deltachi <= 0.245 eV for a singly ionized atom), whereas in a B-star atmosphere Deltachi may become as large as 0.416 eV. Therefore, it is quite clear that the selection of a unique value for Deltachi, may result in a poor determination of the APF-value. The representation of APFs made by Traving et al. has no limitation on temperature range, it gives the correct result for Deltachi <= Deltachilimit (Deltachilimit being a function of the element and its ionization stage) and has the advantage of being computed in single numerical precision. One limitation it has is practical: if used in the analysis of the excitation and ionization equilibrium of a medium with many elements present, the full calculations require excessive computer time; other shortcomings were also found for the Traving et al. formulae, e.g., owing to overestimation of the ionization energy for Li I, Be II, B III, etc., too many terms are added up in the APF computation, and the value so obtained is larger than the right one if Deltachi <= 0.01 eV. In a broad sense, it is shown that the representations of APFs made by Traving et al., Irwin, and Sauval and Tatum, are quite homogeneous and accurate; some exceptions are analyzed. ER - TY - Journal T1 - A new survey for high velocity HI detections in the Southern Hemisphere A1 - Morras, R. A1 - Bajaja, E. A1 - Arnal, E. M. A1 - Pöppel, W. G. L. JO - Astronomy and Astrophysics Supplement Series VL - 142 Y1 - 2000/2/1 SP - 25 EP - 30 KW - SURVEYS/ ISM: CLOUDS/ ISM: KINEMATICS AND DYNAMICS/ GALAXY: HALO/ GALAXY: KINEMATICS AND DYNAMICS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26AS..142...25M&db_key=AST&high=42a068d47512625 N2 - A new high-sensitivity HI survey of the southern sky was made south of Declination -25°, at the Instituto Argentino de Radioastronomía (IAR), on a half-degree grid in galactic coordinates. A total of 50980 positions were observed. One of the goals of this survey was to search for high velocity clouds (HVCs). The HI profiles have been smoothed to a velocity resolution of 8 km s^-1. The resulting rms noise falls in the range 0.015 to 0.020 K. We have detected 6848 high velocity (HV) components. ER - TY - Journal T1 - Complex H: a case of HVC-galaxy collision? A1 - Morras, R. A1 - Bajaja, E. A1 - Arnal, E. M. JO - Astronomy and Astrophysics VL - 334 Y1 - 1998/6/1 SP - 659 EP - 669 KW - ISM: HVC COMPLEX H/ ISM: CLOUDS/ KINEMATICS AND DYNAMICS/ BUBBLES/ RADIO LINES: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26A...334..659M&db_key=AST&high=42a068d47512625 N2 - This work has been undertaken with the intention of studying the interaction between HI high velocity clouds (HVCs) and the galactic HI. For this purpose we have selected the HVC complex known as Complex H, which includes HVC131+1-200, because its low galactic latitude and its size make such interaction very likely. Furthermore, the low latitude lessens the uncertainty about its vertical height above the plane. In order to verify the existence of such interaction, we studied the available observations of the complex and we observed, in the HI 21 cm line, a region centered on HVC131+1-200 with the 100 m Effelsberg telescope. Our map for the distribution of the high velocity HI shows, within the observed region, four peaks, two of them not seen before, and, in some places, steep gradients in the column densities. The latter suggests the existence of shocks which might represent the effects of the interaction on the high velocity cloud. We studied the distribution of the HI at low and intermediate velocities, using the existing surveys of galactic HI covering the region of Complex H, and we found a hole, approximately constant in size and position, within the velocity range of -109 to -98 km s(-1) . Determining kinematical distances, the hole appears to be at about 22 kpc from the galactic center and 15.4 kpc from the Sun. We present arguments that suggest that this hole and Complex H are the results of the collision of a HVC with the galactic HI in a warped region of the Galaxy. Based on observations made with the 100 m telescope of the Max-Planck-Institut fur Radioastronomy in Effelsberg, Germany ER - TY - Journal T1 - Hodge 53-47: an early O-type double-lined binary in the Small Magellanic Cloud^* A1 - Morrell, Nidia A1 - Ostrov, Pablo A1 - Massey, Philip A1 - Gamen, Roberto JO - Monthly Notices of the Royal Astronomical Society VL - 341 Y1 - 2003/5/1 SP - 583 EP - 588 KW - binaries: close/ binaries: eclipsing/ binaries: spectroscopic/ stars: early-type/ stars: fundamental parameters/ stars: individual: Hodge 53-47 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.341..583M&db_key=AST&high=42a068d47514128 N2 - We present a spectroscopic and photometric study of the double-lined binary Hodge 53-47 in the Small Magellanic Cloud. We determine for the binary components spectral types of O6 V + O4-5 III(f). Through a simultaneous light and radial velocity curve analysis via the Wilson-Devinney code we find absolute masses of ~26 M_solar and ~16 M_solar and radii of ~10.1 R_solar and ~8.4 R_solar for the O6 V and O4-5 III(f) components, respectively. The relatively low mass found for the O4-5 III(f) component suggests that mass transfer and loss have played a significant role in the evolution of these stars. ER - TY - Journal T1 - Optical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205 A1 - Morrell, N. I. A1 - Barbá, R. H. A1 - Niemela, V. S. A1 - Corti, M. A. A1 - Albacete Colombo, J. F. A1 - Rauw, G. A1 - Corcoran, M. A1 - Morel, T. A1 - Bertrand, J.-F. A1 - Moffat, A. F. J. A1 - St-Louis, N. JO - Monthly Notices of the Royal Astronomical Society VL - 326 Y1 - 2001/9/1 SP - 85 EP - 94 KW - BINARIES: GENERAL/ STARS: EARLY-TYPE/ STARS: INDIVIDUAL: HD 93205/ X-RAYS: STARS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.326...85M&db_key=AST&high=42a068d47514128 N2 - A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii lambda4686Å (primary component) and Hei lambda4471Å (secondary component) absorption lines yield semi-amplitudes of 133+/-2 and 314+/-2kms^-1 for each binary component, resulting in minimum masses of 31 and 13M_solar (q=0.42). We also confirm for the binary components the spectral classification of O3V+O8V previously assigned. Assuming for the O8V component a `normal' mass of 22-25M_solar we would derive for the primary O3V a mass of `only' 52-60M_solar and an inclination of about 55° for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185+/-16yr using all available radial velocity data sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage are also discussed. ER - TY - Journal T1 - Velocity Dispersions and Cluster Properties in the Southern Abell Redshift Survey Clusters. II. A1 - Muriel, Hernán A1 - Quintana, Hernán A1 - Infante, Leopoldo A1 - Lambas, Diego G. A1 - Way, Michael J. JO - Astronomical Journal VL - 124 Y1 - 2002/10/1 SP - 1934 EP - 1942 KW - Galaxies: Clusters: General/ Galaxies: Distances and Redshifts/ Surveys UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....124.1934M&db_key=AST&high=42a068d47515909 N2 - We report an analysis of the dynamical structure of clusters of galaxies from a survey of photometric and spectroscopic observations in the fields of southern Abell clusters. We analyze the galaxy velocity field in extended regions up to 7 h^-1 Mpc from cluster centers, and we estimate mean velocity dispersions and their radial dependence. Only one from a total of 41 Abell clusters does not correspond to a dynamically bound system. However, four of these bound objects are double clusters. We estimate that 20% (seven clusters) of the 35 remaining are subject to serious projection effects. Normalizing the clustercentric distances by means of the overdensity radius r₂₀₀, and the velocity dispersion profiles (VDPs) by the corresponding mean cluster velocity dispersion, we computed the average VDP. Our results indicate a flat behavior of the mean VDP at large distances from the cluster center. Nevertheless, we found that for the inner part of the clusters (r/r₂₀₀<=1) the VDP is up to 10% smaller than at larger radii. Based on observations collected at Las Campanas Observatory of the Carnegie Institution of Washington. ER - TY - Journal T1 - Galaxy Luminosity Function in Groups A1 - Muriel, Hernán A1 - Valotto, Carlos A. A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 506 Y1 - 1998/10/1 SP - 540 EP - 544 KW - GALAXIES: CLUSTERS: GENERAL/ GALAXIES: LUMINOSITY FUNCTION/ MASS FUNCTION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...506..540M&db_key=AST&high=42a068d47515909 N2 - We compute the luminosity function (LF) of galaxies in groups. The data consist of groups of galaxies selected in distance and redshift space in two samples comprising a total number of 66 groups. The assignment of galaxies to the groups was derived from the Edinburgh-Durham Southern Galaxy Catalog, considering a limiting apparent magnitude m_lim = 19.4. We find a flat faint end of the mean galaxy LF in groups, which is in contrast to the mean galaxy LF in clusters where a large relative number of faint galaxies is present. We find that a Schechter function with parameters M^* ~= -19.6 +/- 0.2, alpha ~= -1.0 +/- 0.2 provides a satisfactory fit to the galaxy LF of our total sample of groups in the range of absolute magnitudes -22 < M < -16. ER - TY - Journal T1 - The Luminosity Function of Elliptical Galaxies A1 - Muriel, Hernan A1 - Nicotra, Mariono A. A1 - Lambas, Diego G. JO - Astronomical Journal VL - 110 Y1 - 1995/9/1 SP - 1032 KW - GALAXIES: ELLIPTICAL AND LENTICULAR/ GALAXIES: LUMINOSITY FUNCTION/ GALAXIES: DISTANCES AND REDSHIFTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995AJ....110.1032M&db_key=AST&high=42a068d47515909 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1032M&db_key=AST ER - TY - Journal T1 - Spatial Structure of Regular and Chaotic Orbits in Self-Consistent Models of Galactic Satellites A1 - Muzzio, J. C. A1 - Mosquera, M. E. JO - Celestial Mechanics and Dynamical Astronomy VL - 88 Y1 - 2004/4/1 SP - 379 EP - 396 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004CeMDA..88..379M&db_key=AST&high=42a068d47516778 N2 - In several previous papers we had investigated the orbits of the stars that make up galactic satellites, finding that many of them were chaotic. Most of the models studied in those works were not self-consistent, the single exception being the Heggie and Ramamani (1995) models; nevertheless, these ones are built from a distribution function that depends on the energy (actually, the Jacobi integral) only, what makes them rather special. Here we built up two self-consistent models of galactic satellites, freezed theirs potential in order to have smooth and stationary fields, and investigated the spatial structure of orbits whose initial positions and velocities were those of the bodies in the self-consistent models. We distinguished between partially chaotic (only one non-zero Lyapunov exponent) and fully chaotic (two non-zero Lyapunov exponents) orbits and showed that, as could be expected from the fact that the former obey an additional local isolating integral, besides the global Jacobi integral, they have different spatial distributions. Moreover, since Lyapunov exponents are computed over finite time intervals, their values reflect the properties of the part of the chaotic sea they are navigating during those intervals and, as a result, when the chaotic orbits are separated in groups of low- and high-valued exponents, significant differences can also be recognized between their spatial distributions. The structure of the satellites can, therefore, be understood as a superposition of several separate subsystems, with different degrees of concentration and trixiality, that can be recognized from the analysis of the Lyapunov exponents of their orbits. ER - TY - Journal T1 - Stellar Motions in Galactic Satellites A1 - Muzzio, Juan C. A1 - Vergne, M. Marcela A1 - Wachlin, Felipe C. A1 - Carpintero, Daniel D. JO - Celestial Mechanics and Dynamical Astronomy VL - 81 Y1 - 2001/9/1 SP - 167 EP - 176 KW - GALACTIC SATELLITES/ STELLAR ORBITS/ CHAOTIC MOTION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001CeMDA..81..167M&db_key=AST&high=42a068d47516778 N2 - The study of the motions of the stars that belong to a galactic satellite (i.e. a globular cluster or a dwarf galaxy orbiting a larger one) has some similarities, as well as significant differences, with that of the restricted three-body problem of celestial mechanics. The high percentage of chaotic orbits present in some models is of particular interest because it rises, on the one hand, the question of the origin of those chaotic motions and, on the other hand, the question of whether an equilibrium stellar system can be built when the bulk of the stars that make it up behave chaotically. ER - TY - Journal T1 - Sinking, Tidally Stripped, Galactic Satellites A1 - Muzzio, Juan C. JO - Celestial Mechanics and Dynamical Astronomy VL - 64 Y1 - 1996/1/1 SP - 69 EP - 78 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996CeMDA..64...69M&db_key=AST&high=42a068d47516778 N2 - Not Available ER - TY - Journal T1 - Massive spectroscopic binaries in the Magellanic Clouds A1 - Niemela, Virpi A1 - Gamen, Roberto JO - New Astronomy Review VL - 48 Y1 - 2004/7/1 SP - 727 EP - 730 KW - Binaries: spectroscopic/ Stars: individual (NGC 346-1)/ Stars: individual (HDE 270145) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004NewAR..48..727N&db_key=AST&high=42a068d47521541 N2 - We present results of our ongoing observing program on search and studies of massive stars (O type) in binary systems in our neighbour galaxies, the Magellanic Clouds. Radial velocity orbits are presented for two new binaries, one in the Small Magellanic Cloud and another in the Large Magellanic Cloud. Fellow of CONICET, Argentina. Visiting Astronomer, CASLEO, Argentina. ER - TY - Journal T1 - The massive Wolf-Rayet binary SMC WR7 A1 - Niemela, V. S. A1 - Massey, P. A1 - Testor, G. A1 - Giménez Benítez, S. JO - Monthly Notices of the Royal Astronomical Society VL - 333 Y1 - 2002/6/1 SP - 347 EP - 352 KW - binaries: spectroscopic/ stars: individual: AzV 336a (=SMC WR7)/ stars: Wolf-Rayet UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.333..347N&db_key=AST&high=42a068d47521541 N2 - We present a study of optical spectra of the Wolf-Rayet star AzV 336a (=SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double-lined WN+O6 spectroscopic binary with an orbital period of 19.56d. The radial velocities of the He absorption lines of the O6 component and the strong HeII emission at lambda4686Å of the WN component describe anti-phased orbital motions. However, they show a small phase shift of ~1d. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of HeII emission is twice that of the absorption lines. The binary components have fairly high minimum masses, ~18 and 34M_solar for the WN and O6 components, respectively. ER - TY - Journal T1 - The nature of Sk -67°18 in the Large Magellanic Cloud: A multiple system with an O3f^* component A1 - Niemela, V. S. A1 - Seggewiss, W. A1 - Moffat, A. F. J. JO - Astronomy and Astrophysics VL - 369 Y1 - 2001/4/1 SP - 544 EP - 551 KW - GALAXIES: INDIVIDUAL: LMC/ STARS: BINARIES: GENERAL/ STARS: EARLY-TYPE/ STARS: INDIVIDUAL: SK -67\DEGR18 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...369..544N&db_key=AST&high=42a068d47521541 N2 - We present the results of photometric and spectroscopic observations obtained between 1980 and 1996, which show that the bright star Sk -67°18 in the Large Magellanic Cloud (LMC) is a multiple star which contains an eclipsing binary system. Our spectra show that this is an Of + O type binary, where the primary is probably of type O3f^*. The orbital period of the eclipsing binary is almost exactly 2 days, which considerably compromises the obtaining of data with suitable phase coverage. Furthermore, from our radial velocity analysis of the spectral lines, Sk -67°18 appears to be a multiple system consisting of at least two pairs of short-period binaries. ER - TY - Journal T1 - The massive Wolf-Rayet binary LSS 1964 (= WR 29) A1 - Niemela, V. S. A1 - Gamen, R. C. JO - Astronomy and Astrophysics VL - 362 Y1 - 2000/10/1 SP - 973 EP - 977 KW - STARS: BINARIES: SPECTROSCOPIC/ STARS: INDIVIDUAL: WR 29/ STARS: WOLF-RAYET UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...362..973N&db_key=AST&high=42a068d47521541 N2 - We present a radial velocity study of LSS 1964 (= WR 29) based on digital spectral images obtained with the 2.15-m telescope at CASLEO, San Juan, Argentina, between 1997 and 2000. We find this star to be a double-lined WN + O binary with a period of 3.16415 days. The WN component appears to be more massive than the O type component. Niv absorption at ~ lambda 5203 Å is found to belong to the WN7 star. ER - TY - Journal T1 - Rapid evolutionary changes in the WR binary HD 5980. A1 - Niemela, V. S. A1 - Barba, R. H. A1 - Morrell, N. I. JO - New Astronomy Review VL - 43 Y1 - 1999/1/1 SP - 475 EP - 480 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999NewAR..43..475N&db_key=AST&high=42a068d47521541 N2 - Not Available ER - TY - Journal T1 - Hubble Space Telescope Detection of Optical Companions of WR 86, WR 146, and WR 147: Wind Collision Model Confirmed A1 - Niemela, Virpi S. A1 - Shara, Michael M. A1 - Wallace, Debra J. A1 - Zurek, David R. A1 - Moffat, Anthony F. J. JO - Astronomical Journal VL - 115 Y1 - 1998/5/1 SP - 2047 EP - 2052 KW - STARS: BINARIES: VISUAL/ STARS: INDIVIDUAL: ALPHANUMERIC: WR 86/ STARS: INDIVIDUAL: ALPHANUMERIC: WR 146/ STARS: INDIVIDUAL: ALPHANUMERIC: WR 147/ STARS: WOLF-RAYET UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....115.2047N&db_key=AST&high=42a068d47521541 N2 - Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of the rado-binary Wolf-Rayet stars WR 146 and WR 147, as well as the 0.2" visual binary WR 86, resolve each of them into two very close optical components. The colors of these optical pairs are similar, indicating that they are likely to be physically bound WR + OB systems at the same distance. Comparison of the locations of the optical components of WR 146 and WR 147 with high-resolution radio maps strikingly demonstrates that the nonthermal radio components arise between the optical binary components, closer to the OB component than the WR. This is as expected if the nonthermal radio emission results from the collision of the stellar winds of the binary components seen in the HST images. The similar magnitudes and colors determined for the components of WR 86 from our HST images, combined with an analysis of the unresolved, combined WC7 + OB optical spectrum, indicates an absolute magnitude for the WC7 component of about M_V ~ -5. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555. ER - TY - Journal T1 - The O5-7 + WN binary system HDE 320102. A1 - Niemela, V. S. A1 - Cabanne, M. L. A1 - Bassino, L. P. JO - Revista Mexicana de Astronomia y Astrofisica VL - 31 Y1 - 1995/4/1 SP - 45 EP - 49 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995RMxAA..31...45N&db_key=AST&high=42a068d47521541 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995RMxAA..31...45N&db_key=AST ER - TY - Journal T1 - Information Entropy an Indicator Of Chaos A1 - Nunez, J. A. A1 - Cincotta, P. M. A1 - Wachlin, F. C. JO - Celestial Mechanics and Dynamical Astronomy VL - 64 Y1 - 1996/1/1 SP - 43 EP - 53 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996CeMDA..64...43N&db_key=AST&high=42a068d47532539 N2 - Not Available ER - TY - Journal T1 - The high-velocity clouds and the Magellanic Clouds A1 - Olano, C. A. JO - Astronomy and Astrophysics VL - 423 Y1 - 2004/9/1 SP - 895 EP - 907 KW - ISM: clouds/ galaxies: Magellanic Clouds/ Galaxy: structure/ Galaxy: halo/ Galaxy: evolution/ galaxies: interactions UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...423..895O&db_key=AST&high=42a068d47501782 N2 - From an analysis of the sky and velocity distributions of the high-velocity clouds (HVCs) we show that the majority of the HVCs has a common origin. We conclude that the HVCs surround the Galaxy, forming a metacloud of ~ 300 kpc in size and with a mass of ~ 3× 10⁹ M_âŠ™, and that they are the product of a powerful ``superwind'' (about 10⁵⁸ ergs), which occurred in the Magellanic Clouds about 570 Myr ago as a consequence of the interaction of the Large and Small Magellanic Clouds. The HVCs might be magnetic bubbles of semi-ionized gas, blown from the Magellanic Clouds around 570 Myr ago, that circulate largely through the halo of the Galaxy as a stream or flow of gas. On the basis of the connection found between the HVCs and the Magellanic Clouds, we have constructed a theoretical model with the purpose of computing the orbits of a sample of test particles representing the HVCs, under the gravitational action of the Galaxy and the Magellanic Clouds. The orbits of the Large and Small Magellanic Clouds have been traced backwards in time to estimate the position and velocity of the Clouds at the time of the collision between the two Clouds, and to infer the initial conditions of the HVCs. The model can reproduce the main features of position and velocity distributions of the HVCs, like the overall structure and kinematics of the Magellanic Stream. The initial velocities of the HVCs were the result of velocities of expansion that permitted the escape of the HVCs from the Magellanic Clouds plus the systemic velocity of the Magellanic Clouds at the time of the collision. With these initial conditions, the Galactic gravitational potential induced differential rotations or shearing motions that elongated the cloud of HVCs in the orbital direction, forming the rear and front parts of the Magellanic stream. The population of HVCs is centered around the Magellanic Clouds. The eccentric position of the Sun within the cloud of HVCs explains the asymmetries between the sky distributions of the HVCs of the northern Galactic hemisphere and those of the southern Galactic hemisphere. In the light of the model we analyze the effects that the passage of the HVC flow through the Galactic disk has produced on the interstellar medium. The effects of the HVC flow can account for many observational details such as the Galactic warp, HI shells and supershells in the gaseous layer of the outer parts of the Milky Way. The Galactic disk was target of numerous impacts of HVCs in the course of the last 400 Myr, accumulating mass at the average rate of approximately 0.6 M_âŠ™ per year. The events of this period may be regarded as landmarks in the evolutionary history of the Milky Way. ER - TY - Journal T1 - The Origin of the Local System of Gas and Stars A1 - Olano, C. A. JO - Astronomical Journal VL - 121 Y1 - 2001/1/1 SP - 295 EP - 308 KW - Galaxy: Structure/ ISM: Clouds/ ISM: Kinematics and Dynamics/ Galaxy: Open Clusters and Associations: Individual: Name: Gould Belt/ Galaxy: Open Clusters and Associations: Individual: Name: Sirius Supercluster/ Galaxy: Solar Neighborhood UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121..295O&db_key=AST&high=42a068d47501782 N2 - We present a model for the local system of gas and stars that we associate essentially with Gould's Belt, the Sirius supercluster, and the Local arm. We consider that these subsystems were formed in different epochs within a supercloud that was initially moving almost ballistically in the Galactic field until an encounter with a major spiral arm started a braking process. The stars of older generations, i.e., the Sirius supercluster, tended to conserve the kinematics of the prebraking phase of the supercloud, while the remaining gas and the early star complexes reflect the recent kinematics, resulting from the braking process. We have calculated back in time the epicyclic orbits of the Sirius supercluster, as well as of the postulated supercloud, starting from adequate initial conditions and taking into account the action of a friction force on the gas. From the condition that the Sirius supercluster and the postulated supercloud shared the same orbits before the separation of gas and stars because of the braking forces, we have determined the free parameters of the model. The main evidence supporting our hypothesis is that the supercloud's track derived from the model coincides with a large ``tunnel'' in the distribution of the local interstellar matter, toward l~240°. We conclude that a supercloud of ~2×10⁷ M_solar and a radius of ~400 pc was the common precursor of the Sirius supercluster, Gould's Belt, and the Local arm. The Sirius supercluster was born ~500 Myr ago in the supercloud, rotating in the Galactic sense and coexisting with the supercloud ever since. We show that the theoretical velocity distribution of the Sirius supercluster derived from the model is consistent with the observed vertex deviation and velocity dispersions of the Sirius supercluster. The supercloud entered into a major spiral arm 100 Myr ago. The interaction with the Galactic shock and the subsequent gas streaming generated a process of braking and compression of the gas in the supercloud. This led to the drifting out of the stars of the Sirius supercluster from the gas and to the formation of Gould's Belt and the Local arm. The results of the model suggest that the interaction with the Galactic shock compressed the gas of the central regions of the supercloud into a flattened disk, precursor of Gould's Belt, whereas the peripheral gas generated an expanding superring, precursor of the Local arm. The observed inclination of Gould's Belt and the Galactic longitude of its nodal line are consistent with the results of the model. To study the initial configuration and the evolution of the kinematics of the local superring in the Galactic force field with interstellar friction forces, we assumed that initially the superring (1) had a cylindrical form with its axis perpendicular to the Galactic plane, (2) was centered at the barycenter that the supercloud had 100 Myr ago, and (3) had a velocity field resulting from the velocity of its own barycenter and the velocity of rotation about it (both conserved from the supercloud), plus a velocity of radial expansion from the center of the ring. The model of the superring fits the configuration of the Local arm and the kinematics of its interstellar matter, i.e., Lindblad's feature C/H, reasonably well. Computing the Sun's orbit for the last 100 Myr, with the help of the supercloud model, we find that the Sun has been attached to the local system. We quote that this interesting fact could give a firm foundation for a Galactic theory of terrestrial catastrophism. Finally, we describe the probable origins of the main stellar streams, i.e., the superclusters in the solar neighborhood, from the point of view of the supercloud model. ER - TY - Journal T1 - Jupiter's Synchrotron Emission Induced by the Collision of Comet Shoemaker-Levy 9 A1 - Olano, C. A. JO - Astrophysics and Space Science VL - 266 Y1 - 1999/1/1 SP - 347 EP - 369 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999Ap%26SS.266..347O&db_key=AST&high=42a068d47501782 N2 - From July 13 to August 21, 1994, we observed Jupiter at 1420 MHz using one of the 30-m single dishes of the Instituto Argentino de Radioastronomía. After the impact of fragment G, we detected a rapid increase of the 21cm-continuum flux, which reached the maximum (~ 20% of Jupiter's flux) at the end of the impact period. The nature of this radiation is clearly synchrotron. We interpret it in terms of a new population of relativistic electrons (~ 2 x 10^29) injected into the Jovian magnetosphere as a consequence of the impact explosions. The proposed mechanism is that the relativistic plasma was blown as magnetic clouds that flowed along the magnetic lines of force towards the jovimagnetic equator. We constructed a model in which the energies of the fresh electrons, generated within the magnetized clouds with a power law energy spectrum, were highly degraded by the comet dust grains attached to the magnetized plasma. The model can account for the spectral shape based on observations at several frequencies (de Pater et al., 1995, Science 268, 1879; Venturi et al., 1996, Astron. Astrophys. 316, 243). The energy released by the explosions under the form of relativistic electrons is of ~ 2 x 10^25 erg, which represents a fraction of about 1-3 per cent of the explosion energy. The efficiency in converting the explosion energy into the relativistic electron energy is, therefore, of the same order of magnitude as that of supernova explosions. An alternative model is considered. This gives figures for the total energy and number of relativistic electrons that are similar to the corresponding ones of the favoured model. Finally, we suggest that the behavior of the flux decay in the various observed frequencies is the result of the diffusion of electrons into the loss-cone due to the resonant scattering of the electrons by Alfven waves. ER - TY - Journal T1 - Pismis 20: One or two clusters? A1 - Orsatti, A. M. A1 - Vega, E. I. A1 - Marraco, H. G. JO - Astronomy and Astrophysics VL - 408 Y1 - 2003/9/1 SP - 135 EP - 140 KW - ISM: dust/ extinction/ open clusters and associations: individual: Pis20/ stars: individual: WR67/ technique: polarimetric UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...408..135O&db_key=AST&high=42a068d47503514 N2 - We present UBVRI polarimetric observations of stars in the direction of the open cluster Pismis 20 and WR 67. It is found that the observed members segregate polarimetrically into two groups, with different associated mean P_max (4.31 and 6.08% respectively). Although in the literature these stars are considered as members of the same cluster, the polarized light from these groups clearly differs. There are two possible explanations: very efficient polarizing dust particles exists between certain members of the cluster; or else Pismis 20 is composed of different groupings superimposed along the line of sight. WR 67 belongs to the group more affected by the dust. Based on observations obtained at Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - A polarimetric view of the open cluster Lyngå 6 and the Cepheid TW Normæ A1 - Orsatti, A. M. A1 - Vega, E. I. A1 - Marraco, H. G. JO - Astronomy and Astrophysics VL - 380 Y1 - 2001/12/1 SP - 130 EP - 136 KW - ISM: DUST/ EXTINCTION/ OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL (LYNGÅ 6)/ STARS: INDIVIDUAL TW NOR UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...380..130O&db_key=AST&high=42a068d47503514 N2 - We present UBVRI polarimetric observations of stars belonging to the small open cluster Lyngå 6 and of TW Nor, a Cepheid which can be seen near the center of the grouping. The wavelength of maximum polarization is computed and then analyzed in the context of its relation to the optical properties and characteristic particle size distribution of the grains responsible for the polarization. The amount and direction of linear polarization is also computed. Results indicate a mean polarization efficiency close to the value found for the interstellar medium. Two out of seven members of Lyngå 6 present indications of intrinsic polarization in their measures. We conclude that part of the polarization detected in the light from members of the cluster comes from a dust cloud located in the Local arm, at a distance of about 1 kpc. In general, polarization measurements do not support the membership of TW Nor to Lyngå 6. ER - TY - Journal T1 - Dust properties in NGC 6611 A1 - Orsatti, A. M. A1 - Vega, E. I. A1 - Marraco, H. G. JO - Astronomy and Astrophysics Supplement Series VL - 144 Y1 - 2000/6/1 SP - 195 EP - 202 KW - ISM: DUST/ EXTINCTION/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL (NGC 6611)/ ISM: HII REGIONS/ ISM: MAGNETIC FIELDS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26AS..144..195O&db_key=AST&high=42a068d47503514 N2 - An investigation on dust properties in the NW portion of NGC 6611 has been conducted polarimetrically to test the existence of abnormal extinction in that section of the open cluster in an independent way. As previously suggested for the eta Carinae nebula by Tapia et al. (\cite{TRMR88b}) and subsequently confirmed by Marraco et al. (\cite{MVV93}), the canonical relation between {E_{ V-K}/E_{ B-V}} and lambda_max (the wavelength of maximun interstellar polarization) is not valid for stars belonging to dusty H ii regions, as is the case for the observed portion of M 16. This may arise mainly from the presence of silicate grains of a slightly larger size than the standard ISM and also from a considerable increase in mean graphite grain size, according to previous results from Chini & Wargau (\cite{CW90}). About 50% of the observed stars in NGC 6611 present indications of intrinsic polarization in their measurements; a similar percentage was found in IC 2944 (Vega et al. \cite{VOM94}), another young open cluster in close relation with an H ii region. Table 1 only available in electronic form at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - Polarimetry of the Highly Reddened Open Clusters HOGG 15 and Lyngå 14 A1 - Orsatti, A. M. A1 - Vega, E. A1 - Marraco, H. G. JO - Astronomical Journal VL - 116 Y1 - 1998/7/1 SP - 266 EP - 273 KW - ISM: DUST/ EXTINCTION/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NAME: HOGG 15/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NAME: LYNGÅ 14 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116..266O&db_key=AST&high=42a068d47503514 N2 - We present UBVRI polarimetric observations of stars belonging to the highly reddened open clusters Hogg 15 and Lyngå 14. The wavelength of maximum polarization is computed and then analyzed in the context of its relation to the optical properties and characteristic particle size distribution of the grains responsible for the polarization in each case. The amount and direction of the linear polarization are also computed. Results indicate that the polarization efficiency is relatively low in both cases, compared with the values attributed to the interstellar medium, and probably due to depolarization effects. Only one out of the 12 observed members in Hogg 15, and none in Lyngå 14, presents indications of intrinsic polarization in its measures. There exists some ``intracluster'' dust in association with Hogg 15, with a slightly different grain size distribution when compared with the Coalsack dust itself. For Lyngå 14, we conclude that the polarization detected in this case possibly comes from dust present in a nearby cloud located along the line of sight to the cluster, with some dust related to the cluster itself. The magnetic field in the direction to Hogg 15 follows the general trend of the polarization directions in the region, but this is not true for Lyngå 14, where differences seem to exist. Based on observations at the Complejo Astronómico El Leoncito, operated under agreement among the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, Secretaría de Ciencia y Tecnología de la Nación, and the National Universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - Ruprecht 55 or the Two-In-One Cluster A1 - Orsatti, A. M. JO - Astronomical Journal VL - 110 Y1 - 1995/10/1 SP - 1728 KW - OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: RUPRECHT 55/ STARS: EARLY-TYPE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995AJ....110.1728O&db_key=AST&high=42a068d47503514 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1728O&db_key=AST ER - TY - Journal T1 - The O4f + O6V eclipsing binary system Sk-67°105 in the Large Magellanic Cloud A1 - Ostrov, Pablo G. A1 - Lapasset, Emilio JO - Monthly Notices of the Royal Astronomical Society VL - 338 Y1 - 2003/1/1 SP - 141 EP - 146 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.338..141O&db_key=AST&high=42a068d47507413 N2 - We present a new V light curve of the early type Magellanic eclipsing binary Sk-67°105, based on charge-coupled device images obtained at CASLEO. We perform an analysis of our data, together with published radial velocities, deriving the following masses and radii: M₁= 48.3 M_solar, R₁= 16.9 R_solar for the O4f component and M₂= 31.4 M_solar, R₂= 13.8 R_solar for the O6 component. We found that this system is the brightest member of a tight star cluster, belonging to an OB association. ER - TY - Journal T1 - A very massive spectroscopic binary in the LH 54 OB association in the Large Magellanic Cloud A1 - Ostrov, Pablo G. JO - Monthly Notices of the Royal Astronomical Society VL - 336 Y1 - 2002/10/1 SP - 309 EP - 314 KW - binaries: eclipsing/ stars: early-type/ stars: fundamental parameters/ stars: individual: LH 54-425/ Magellanic Clouds UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.336..309O&db_key=AST&high=42a068d47507413 N2 - We announce the discovery of a new early-type, double-lined spectroscopic binary in the LH 54 OB association in the Large Magellanic Cloud. We present a V light curve and radial velocities. We investigate the possible configurations of the system, concluding that it probably contains the most massive star measured at the present, with a mass of the order of 100 M_solar, while its companion has approximately 50 M_solar. ER - TY - Journal T1 - BV photometry of stars in the field of HV2543 A1 - Ostrov, P. G. JO - Journal of Astronomical Data VL - 7 Y1 - 2001/12/1 SP - 2 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001JAD.....7....2O&db_key=AST&high=42a068d47507413 N2 - BV profile fitting photometry in the surroundings of the LMC-eclipsing binary HV2543 is presented here, together with time resolved V aperture photometry for the 100 brightest stars in the field. The data were obtained with the 2.15-m telescope at CASLEO, during three observing runs in 1995, 1997 and 1998. ER - TY - Journal T1 - Fundamental parameters for the eclipsing binary AzV 73 in the Small Magellanic Cloud A1 - Ostrov, P. G. JO - Astronomy and Astrophysics VL - 380 Y1 - 2001/12/1 SP - 258 EP - 263 KW - BINARIES: ECLIPSING/ STARS: EARLY-TYPE/ STARS: FUNDAMENTAL PARAMETERS/ STARS: INDIVIDUAL: \OBJECT{AZV 73 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...380..258O&db_key=AST&high=42a068d47507413 N2 - A CCD V light curve for the eclipsing binary star AzV 73 is presented. This new photometric observations are analysed together with previously published CCD I photometry from Udalski et al. (\cite{uda}) and spectrographic data from Niemela & Bassino (\cite{virpi}), by means of the Wilson-Devinney code. It is found that this system is semi-detached, with an orbital inclination of roughly 86 degr and a separation of 42 R_sun. The sizes and masses are R₁=11.53 +/- 0.5 R_sun, M₁=25.26 +/- 0.7 M_sun, and R₂=15.46 +/- 0.4 R_sun, M₂=21.96 +/- 0.8 M_sun for the primary and secondary components, respectively. ER - TY - Journal T1 - Investigation of the Magellanic eclipsing binary HV 2241 A1 - Ostrov, P. G. A1 - Morrell, N. I. A1 - Lapasset, E. JO - Astronomy and Astrophysics VL - 377 Y1 - 2001/10/1 SP - 972 EP - 980 KW - BINARIES: ECLIPSING/ STARS: EARLY-TYPE/ STARS: FUNDAMENTAL PARAMETERS/ STARS: INDIVIDUAL: HV 2241 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...377..972O&db_key=AST&high=42a068d47507413 N2 - We present a CCD V light curve of HV 2241, together with some observations in the B band. We analysed our photometric data jointly with previously published radial velocities by means of the Wilson-Devinney code, and derived new values for the physical parameters of this massive eclipsing binary system. We confirm that this system is semi-detached, with the secondary (less massive and less luminous component) filling its Roche-lobe. From our analysis, we estimate the following masses and radii for the components of HV 2241: M₁= 36.2 +/- 0.7 M_sun, R₁=14.9 +/- 0.4 R_sun, M₂=18.4 +/- 0.7 {M}_sun and R_2=13.7 +/- 0.4 R_sun. We review the spectral classification analysing HST and IUE data and discuss the temperature and the reddening for this star. ER - TY - Journal T1 - Orbital solution for the MACHO*05:34:41.3-69:31:39 O3If*+O6:V eclipsing binary system in the Large Magellanic Cloud A1 - Ostrov, P. G. JO - Monthly Notices of the Royal Astronomical Society VL - 321 Y1 - 2001/2/1 SP - L25 EP - L28 KW - BINARIES: ECLIPSING/ STARS: EARLY-TYPE/ STARS: FUNDAMENTAL PARAMETERS/ STARS: INDIVIDUAL: MACHO UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.321L..25O&db_key=AST&high=42a068d47507413 N2 - An orbital solution for the MACHO*05:34:41.3-69:31:39 eclipsing binary system is presented, based on the published light curve and spectral data obtained with the 2.15-m telescope at CASLEO. Based on these spectroscopic observations, the binary components of this system were classified as O3If* and O6:V respectively. The radial velocity data along with the published light curve were analysed with the Wilson-Devinney code to derive the following masses and radii for the components of this system: M₁=41+/-1.2M_solar, R₁=9.6+/-0.02R_solar, M₂=27+/-1.2M_solar and R₂=8.0+/-0.05R_solar. The solution shows that the system is in overcontact, as one would expect from the derived masses and the very short orbital period (~1.4d). ER - TY - Journal T1 - Determination of masses and radii of the massive eclipsing binary system HV 2543 in the Large Magellanic Cloud A1 - Ostrov, P. G. A1 - Lapasset, E. A1 - Morrell, N. I. JO - Astronomy and Astrophysics VL - 356 Y1 - 2000/4/1 SP - 935 EP - 942 KW - STARS: BINARIES: ECLIPSING/ STARS: FUNDAMENTAL PARAMETERS/ STARS: EARLY-TYPE/ STARS: INDIVIDUAL: HV 2543 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...356..935O&db_key=AST&high=42a068d47507413 N2 - We present a V light curve of the eclipsing binary system HV 2543 (Sk-67.117 degr) in the Large Magellanic Cloud based on CCD images acquired between the years 1995 and 1998. We have analysed this light curve and published radial velocity data, finding that this system is semidetached, with the secondary (less massive and less luminous component) filling its Roche lobe. From our analysis with the Wilson-Devinney code, we estimated the following masses and radii for the components of HV 2543: M_1=25.63 +/- 0.7 M_sun, R_1=15.54 +/- 0.4 R_sun, M_2=15.63 +/- 1.0 M_sun and R_2=13.99 +/- 0.4 R_sun. On the basis of B and V photometry of the field stars, we found that HV 2543 is member of an OB association, perhaps related to which the massive binary system Sk-67.105 degr belongs. ER - TY - Journal T1 - The NGC 1399 Globular Cluster System: Washington Photometry Revisited A1 - Ostrov, Pablo G. A1 - Forte, Juan C. A1 - Geisler, Doug JO - Astronomical Journal VL - 116 Y1 - 1998/12/1 SP - 2854 EP - 2865 KW - GALAXIES: INDIVIDUAL: NGC NUMBER: NGC 1399/ GALAXIES: STAR CLUSTERS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116.2854O&db_key=AST&high=42a068d47507413 N2 - A new analysis and discussion of Washington CCD photometry for some 500 globular cluster candidates associated with the Fornax cluster cD galaxy NGC 1399 are presented. The image handling in this work includes improved methods for the removal of both the galaxy halo and fringing effects over that employed in a previous work of ours. The analysis of the globular cluster candidates inside an annular region between 0.5' and 4' from the galaxy center using two-color diagrams shows a clear bimodal distribution for objects fainter than T_1 = 21.0 (V ~ 21.5). The modal colors of the globular clusters belonging to the red population are coincident, within the measuring uncertainties, with those of the galaxy halo. In turn, the average integrated colors of the blue population are comparable to those of the bluest non-star-forming low surface brightness galaxies in Fornax. Red clusters appear more centrally concentrated than the blue clusters. A new determination of the integrated luminosity function turnover (T_1 = 23.24) leads to a distance modulus for NGC 1399 of V_0 - M_V = 31.02 +/- 0.2. The total number of globular clusters, combined with our preliminary photometry of the galaxy halo, leads to an overall specific frequency S_N = 5.6 +/- 1.0, which is considerably lower than previous estimates available in the literature. We note that these last values have been based on an extrapolation of aperture photometry of the inner regions of the galaxy. ER - TY - Journal T1 - A Method to Filter Fringe Patterns in CCD Images A1 - Ostrov, Pablo G. JO - Publications of the Astronomical Society of the Pacific VL - 109 Y1 - 1997/3/1 SP - 338 EP - 340 KW - TECHNIQUES: IMAGE PROCESSING/ METHODS: DATA ANALYSIS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997PASP..109..338O&db_key=AST&high=42a068d47507413 N2 - A technique to remove fringe pattern noise is presented. The method consists in the application of a median filtering technique within a moving window which is "aligned" with fringes at every point of the pattern. This procedure allows one to remove the bulk of noise in fringe patterns without destroying them and, hence, diminishing the final noise in the reduced program images. (SECTION: Computing and Data Analysis) ER - TY - Journal T1 - Mass-radius relations for white dwarf stars of different internal compositions A1 - Panei, J. A. A1 - Althaus, L. G. A1 - Benvenuto, O. G. JO - Astronomy and Astrophysics VL - 353 Y1 - 2000/1/1 SP - 970 EP - 977 KW - STARS: EVOLUTION/ STARS: FUNDAMENTAL PARAMETERS/ STARS: INTERIORS/ STARS: WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...353..970P&db_key=AST&high=42a068d47508329 N2 - The purpose of this work is to present accurate and detailed mass-radius relations for white dwarf (WD) models with helium, carbon, oxygen, silicon and iron cores, and with and without a hydrogen envelope, by using a fully updated stellar evolutionary code. We considered masses from 0.15 M_sun to 0.5 M_sun for the case of helium core, from 0.45 M_sun to 1.2 M_sun for carbon, oxygen and silicon cores, and from 0.45 M_sun to 1.0 M_sun for the case of an iron core. In view of the recent measurements made by Hipparcos that strongly suggest the existence of WDs with an iron-dominated core, we focus our attention mainly on the finite-temperature, mass-radius relations for WD models with iron interiors. In addition, we explore the effects of gravitational, chemical and thermal diffusion on low mass helium white dwarf models with hydrogen and helium envelopes. ER - TY - Journal T1 - Satellite and ground measurements of solar erythemal UV radiation and ozone in Argentina A1 - Piacentini, R. D. A1 - Luccini, E. A1 - Micheletti, M. I. A1 - Quel, E. A1 - Wolfram, E. A. A1 - Pazmiño, A. F. A1 - Fochesatto, J. A1 - Crino, E. A1 - Cede, A. A1 - Blumthaler, M. A1 - Herman, J. A1 - Godin-Beekmann, S. A1 - Mégie, G. JO - Advances in Space Research VL - 34 Y1 - 2004/1/1 SP - 2221 EP - 2226 KW - Solar erythermal UV radiation/ Ozone/ Satellite and ground measurements/ Argentina/ TOMS measurements UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..34.2221P&db_key=AST&high=42a068d47501839 N2 - Solar erythemal UV radiation incident on Argentina from tropical to high latitude regions has been measured with ground-based instruments as well as with the TOMS instrument on board of the NASA Earth-Probe satellite. These data permit validation of the UV index, a measure of solar risk to UV exposure, forecasted daily by CONAE (Argentina National Commission on Space Activities) and the Argentine National Weather Service. Model calculations of this index are also presented. In addition, we analyzed the UV effects from the Antarctic ozone hole passing over the continental part of the country using TOMS data corrected by a factor derived front the intercomparison of TOMS satellite data with those determined with Southern Hemisphere ground-based spectroradiometers. In this way, we obtained a rather comprehensive description of the amount of erythemal UV radiation and consequently of the UV index for the entire country, as well as the ozone total column and profile (the latter one at Buenos Aires). The results presented in this work were determined through collaboration between the following institutions: GSFC/NASA in USA, Institute Pierre Simon Laplace in France, University of Innsbruck in Austria and CEILAP, IFIR, CONAE, SMN, Universities of Rosario and San Luis in Argentina. The need to use erythemal irradiance and ozone results in Argentina, one of the most exposed regions of the Southern Hemisphere to study the effects of ozone depletion and consequently UV detrimental effects, has been partially covered in the framework of this North-South collaboration. ER - TY - Journal T1 - Determination of the UV solar risk in Argentina with high-resolution maps calculated using TOMS ozone climatology A1 - Piacentini, Rubén D. A1 - Cede, Alexander A1 - Luccini, Eduardo A1 - Stengel, Fernando JO - Advances in Space Research VL - 34 Y1 - 2004/1/1 SP - 2215 EP - 2220 KW - UV solar risk in Argentina/ High-resolution maps/ TOMS ozone climatology UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..34.2215P&db_key=AST&high=42a068d47501839 N2 - The connection between ultraviolet (UV) radiation and various skin diseases is well known. In this work, we present the computer program ``UVARG'', developed in order to prevent the risk of getting sunburn for persons exposed to solar UV radiation in Argentina, a country that extends from low (tropical) to high southern hemisphere latitudes. The software calculates the so-called ``erythemal irradiance'', i.e., the spectral irradiance weighted by the McKinlay and Diffey action spectrum for erythema and integrated in wavelength. The erythemal irradiance depends mainly on the following geophysical parameters: solar elevation, total ozone column, surface altitude, surface albedo, total aerosol optical depth and Sun-Earth distance. Minor corrections are due to the variability in the vertical ozone, aerosol, pressure, humidity and temperature profiles and the extraterrestrial spectral solar UV irradiance. Key parameter in the software is a total ozone column climatology incorporating monthly averages, standard deviations and tendencies for the particular geographical situation of Argentina that was obtained from TOMS/NASA satellite data from 1978 to 2000. Different skin types are considered in order to determine the sunburn risk at any time of the day and any day of the year, with and without sunscreen protection. We prescrit examples of the software for three diffèrent regions: the high altitude tropical Puna of Atacama desert in the North-West, Tierra del Fuego in the South when the ozone hole event overpasses and low summer-time ozone conditions over Buenos Aires, the largest populated city in the country. In particular, we analyzed the maximum time for persons having diffèrent skin types during representative days of the year (southern hemisphere equinoxes and solstices). This work was made possible by the collaboration between the Argentine Skin Cancer Foundation, the Institute of Physics Rosario (CONICET-National University of Rosario, Argentina) and the Institute of Medical Physics, University of Innsbruck, Austria. With the teamwork of physicians and physicists, a scientifically reliable and easy-to-handle tool was developed to predict the risk of solar exposure in Argentina. It cari be used by dermatologists as well as health authorities and educators in order to prevent health problems induced by solar UV radiation. ER - TY - Journal T1 - Intercomparison between ground based and TOMS/EP satellite southern hemisphere ozone data. New results A1 - Piacentini, R. D. A1 - Crino, E. A1 - Sirur Flores, J. A1 - Ginzburg, M. JO - Advances in Space Research VL - 29 Y1 - 2002/1/1 SP - 1643 EP - 1648 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AdSpR..29.1643P&db_key=AST&high=42a068d47501839 N2 - We present new results of the intercomparison between ozone total column data registered at the Southern Hemisphere with the World Meteorological Organization ground stations of the Southern Cone Ozone Project placed in Uruguay, Argentina and the Antarctic continent, with the Total Ozone Mapping Spectrometer (TOMS) instrument on board the Earth Probe satellite and with the Global Ozone Monitoring Experiment (GOME) instrument on board the Earth Remote Sensing (ERS-2) satellite. At least for the region and period considered, GOME/ERS-2 ozone data gives lower mean systematic relative difference (-1.4 3.2) % than TOMS/EP (4.8 2.7) % with respect to groundspectroradiometers. An analysis of possible causes for the large systematic difference in this last case has been considered: differences with respect to a similar instrument placed in another satellite both measuring the same geophysical variable at different orbits; difference with respect to GOME/ERS-2 satellite measurements in the entire region; possible influence on TOMS data of the difference in reflectivity at the high latitude ice (snow)-sea boundary. ER - TY - Journal T1 - Improvements on the fundamental parameters of the open cluster Tombaugh 1 through Washington system photometry A1 - Piatti, A. E. A1 - Clariá, J. J. A1 - Ahumada, A. V. JO - Astronomy and Astrophysics VL - 421 Y1 - 2004/7/1 SP - 991 EP - 999 KW - Galaxy: open clusters and associations: individual: Tombaugh 1/ Galaxy: general/ techniques: photometric UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...421..991P&db_key=AST&high=42a068d47501468 N2 - We present CCD photometry in the Washington system C and T₁ passbands down to T₁ ~ 18.5 mag in the field of Tombaugh 1, a little studied open cluster located in the third Galactic quadrant. We measured T₁ magnitudes and C-T₁ colours for a total of 1351 stars distributed throughout an area of 13.6 arcmin × 13.6 arcmin. A cluster radius of 4.3 arcmin ± 0.3 arcmin was estimated from star counts in 100-pixel a side boxes distributed throughout the entire observed field. Based on the best fits of isochrones computed by the Geneva group for Z = 0.008 to the T₁ vs. C-T₁ colour-magnitude diagram, we derive a colour excess E(C-T₁) = 0.55 ± 0.10, equivalent to E(B-V) = 0.30 ± 0.05, a distance of (2.2 ± 0.5) kpc from the Sun and an age of 1.3 ^+0.1_-0.2 Gyr. The latter value is in good agreement with that derived from the independent metallicity deltaT₁ index defined in Geisler et al. (1997, AJ, 114, 1920). An independent metallicity estimation using the [M_{T_1}, (C-T₁)₀] plane with the standard giant branches of Geisler & Sarajedini (1999, AJ, 117, 308) yields [Fe/H] = -0.30 ± 0.25 dex, a value which lends support to the one obtained from the isochrone fit. Tombaugh 1 is then found to be a relatively metal-poor intermediate-age open cluster. ER - TY - Journal T1 - The relatively young, metal-poor and distant open cluster NGC 2324 A1 - Piatti, A. E. A1 - Clariá, J. J. A1 - Ahumada, A. V. JO - Astronomy and Astrophysics VL - 418 Y1 - 2004/5/1 SP - 979 EP - 988 KW - Galaxy: open clusters and associations: individual: NGC 2324/ Galaxy: general/ techniques: photometric UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...418..979P&db_key=AST&high=42a068d47501468 N2 - We have obtained CCD photometry in the Johnson V, Kron-Cousins I and CT₁ Washington systems for NGC 2324, a rich open cluster located ~35° from the Galactic anticentre direction. We measured V magnitudes and V-I colours for 2865 stars and T₁ magnitudes and C-T₁ colours for 1815 stars in an area of 13.6 arcmin × 13.6 arcmin. The comparison of the cluster colour-magnitude diagrams with isochrones of the Geneva group yield E(V-I) = 0.33 ± 0.07 and V-M_V = 13.70 ± 0.15 for log t = 8.65 (t = 440 Myr) and Z = 0.008 ([Fe/H] = -0.40), and E(C-T₁) = 0.40 ± 0.10 and T₁-M_T1 = 13.65 ± 0.15 for the same age and metallicity level. The resulting E(V-I) reddening value implies E(B-V) = 0.25 ± 0.05 and a distance from the Sun of (3.8 ± 0.5) kpc. Star counts carried out within and outside the cluster region allowed us to estimate the cluster angular radius as 5.3 arcmin ± 0.3 arcmin (5.9 pc). When using the E(B-V) reddening value here derived and the original Washington photometric data of \citet{gcm91} for the stars confirmed as red cluster giants from Coravel radial velocities, we found [Fe/H] = -0.31 ± 0.04, which is in good agreement with the best fits of isochrones. Therefore, NGC 2324 is found to be a relatively young, metal-poor and distant open cluster located beyond the Perseus spiral arm. A comparison of NGC 2324 with 10 well-known open clusters of nearly the same age shows that the cluster metal abundance and its position in the Galaxy are consistent with the existence of a radial abundance gradient of -0.07 dex kpc^-1 in the Galactic disc. ER - TY - Journal T1 - The old open cluster Trumpler 5: a reddened, metal-poor anticentre cluster A1 - Piatti, Andrés E. A1 - Clariá, Juan J. A1 - Ahumada, Andrea V. JO - Monthly Notices of the Royal Astronomical Society VL - 349 Y1 - 2004/4/1 SP - 641 EP - 648 KW - techniques: photometric/ open clusters and associations: general/ open clusters and associations: individual: Trumpler 5 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.349..641P&db_key=AST&high=42a068d47501468 N2 - CCD observations in the Johnson V, Kron-Cousins I and the Washington system C and T₁ passbands have been used to generate colour-magnitude diagrams (CMDs) reaching down to V~ 21.0 mag and T₁~ 19.0 for Trumpler 5, an old open cluster located towards the Galactic anticentre. Our data analysis confirms the existence of non-uniform extinction over the face of the cluster, the mean E(V-I) and E(C-T₁) values being 0.80 +/- 0.05 and 1.17 +/- 0.15, respectively. Through comparison of the cluster CMDs with theoretical isochrones of the Geneva group, Washington Standard Giant Branches and measures of deltaV and deltaT₁ indices, we derive the following values for the cluster apparent distance modulus, age, and metallicity: V-M_V= 13.80 +/- 0.30 (corresponding to a distance from the Sun of 2.4 +/- 0.5 kpc and 0.04 kpc above the Galactic plane), t= 5.0 +/- 0.5 Gyr and [Fe/H]=-0.30 +/- 0.15. We estimate the cluster angular radius to be about 7.7 arcmin (=5.4 pc) from star counts carried out within and outside the cluster field. ER - TY - Journal T1 - Intermediate-age Galactic open clusters: fundamental parameters of NGC 2627 A1 - Piatti, Andrés E. A1 - Clariá, Juan J. A1 - Ahumada, Andrea V. JO - Monthly Notices of the Royal Astronomical Society VL - 346 Y1 - 2003/12/1 SP - 390 EP - 402 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.346..390P&db_key=AST&high=42a068d47501468 N2 - Charge-coupled device (CCD) photometry in the Johnson V, Kron-Cousins I and Washington CMT₁ systems is presented in the field of the poorly known open cluster NGC 2627. Four independent Washington abundance indices yield a mean cluster metallicity of [Fe/H]=-0.12 +/- 0.08, which is compatible with the existence of a radial gradient in the Galactic disc. The resultant colour-magnitude diagrams indicate that the cluster is an intermediate-age object of 1.4 Gyr. Based on the best fits of the Geneva group's isochrones to the (V, V-I) and (T₁, C-T₁) diagrams, we estimate E(V-I) = 0.25 +/- 0.05 and V-M_V= 11.80 +/- 0.25 for logt= 9.15, and E(C-T₁) = 0.23 +/- 0.07 and T₁-M_T₁= 11.85 +/- 0.25 for logt= 9.10, respectively, assuming solar metal content. The derived reddening value E(C-T₁) implies E(B-V) = 0.12 +/- 0.07 and a distance from the Sun of 2.0 +/- 0.4 kpc. Using the WEBDA data base and the available literature, we re-examined the overall properties of all the open clusters with ages between 0.6 and 2.5 Gyr. We identified peaks of cluster formation at 0.7-0.8, 1.0-1.1, 1.6-1.7 and 2.0-2.1 Gyr, separated by relative quiescent epochs of ~0.2-0.3 Gyr. We also estimated a radial abundance gradient of -0.08 +/- 0.02, which is consistent with the most recent determinations for the Galactic disc, but no clear evidence for a gradient perpendicular to the Galactic plane is found. ER - TY - Journal T1 - Fundamental parameters of the LMC clusters NGC 1836, NGC 1860, NGC 1865, SL 444, LW 224 and SL 548 A1 - Piatti, Andrés E. A1 - Bica, Eduardo A1 - Geisler, Doug A1 - Clariá, Juan J. JO - Monthly Notices of the Royal Astronomical Society VL - 344 Y1 - 2003/9/1 SP - 965 EP - 977 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.344..965P&db_key=AST&high=42a068d47501468 N2 - Complementing our recent Washington photometric studies on intermediate age and young Large Magellanic Cloud (LMC) clusters, we now turn our attention to six previously unstudied star clusters in the transition range 200-700 Myr. We study NGC 1836, 1860 and 1865, which are projected on the LMC bar; SL 444, also located in the central disc but outside the bar; and LW 224 and SL 548, both located in the outer disc. We derive ages and metallicities from extracted T₁ versus C-T₁ colour-magnitude diagrams (CMDs), using theoretical isochrones recently computed for the Washington photometric system. For the metallicity determinations, these CMDs are particularly sensitive. We also estimate ages and metallicities of the surrounding fields of NGC 1860 and 1865 by employing the deltaT₁ index defined in Geisler et al. (1997, AJ, 114, 1920) and theoretical isochrones. By adding the present cluster sample to those of our previous studies, we now gather 37 LMC clusters with homogeneous parameter determinations, which are employed to probe the chemical enrichment of the LMC and its spatial distribution. On average, inner disc clusters turned out to be not only younger than the outer ones, but also more metal-rich; some have solar metal content. Furthermore, inner clusters located to the west of the LMC centre are younger and more metal-rich than their eastern counterparts. We propose that a bursting formation mechanism, with an important formation event centred at ~2.0 Gyr, provides a better description of the cluster age-metallicity relation than a closed-box chemical evolution model. In the outer disc, the field star formation seems to have lasted until 2 Gyr ago while it continued in the inner disc for almost 1 Gyr longer. ER - TY - Journal T1 - Young star clusters immersed in intermediate-age fields in the Large Magellanic Cloud bar A1 - Piatti, Andrés E. A1 - Geisler, Doug A1 - Bica, Eduardo A1 - Clariá, Juan J. JO - Monthly Notices of the Royal Astronomical Society VL - 343 Y1 - 2003/8/1 SP - 851 EP - 862 KW - techniques: photometric/ galaxies: individual: Large Magellanic Cloud/ Magellanic Clouds/ galaxies: star clusters UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.343..851P&db_key=AST&high=42a068d47501468 N2 - We present Washington System photometry for 11 star clusters immersed in the north-west part of the Large Magellanic Cloud (LMC) bar, centred on the intermediate-age clusters NGC 1865 and SL 244. The fields are heavily populated by the intermediate-age component of the LMC bar. We succeeded in disentangling cluster colour-magnitude diagrams from those of the fields and in deriving reddening and ages for five clusters - SL 218, BRHT4b, and NGC 1839, 1838 and 1863 - with the aid of recent Washington System theoretical isochrones. The resulting cluster ages range between 50 and 125 Myr. Despite their proximity, NGC 1836 and BRHT4b have very different ages. Thus the possibility of these two objects being a binary cluster is very unlikely, although a capture cannot be ruled out a priori. Our results suggest that for each intermediate-age cluster remaining in the LMC bar region, a number of robust young blue star clusters occurs in the same region. ER - TY - Journal T1 - The relatively young and metal-poor Galactic open cluster NGC 2194 A1 - Piatti, Andrés E. A1 - Clariá, Juan J. A1 - Ahumada, Andrea V. JO - Monthly Notices of the Royal Astronomical Society VL - 340 Y1 - 2003/4/1 SP - 1249 EP - 1260 KW - techniques: photometric/ open clusters and associations: general/ open clusters and associations: individual: NGC 2194 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.340.1249P&db_key=AST&high=42a068d47501468 N2 - We present CCD VI_KC photometry down to V~ 21 mag in the field of the rich open cluster NGC 2194, which is projected towards the Galactic anticentre direction. We measured V magnitudes and V-I colours for a total of 2515 stars in a field of 13.6 × 13.6 arcmin². These data are supplemented with CCD photometry in the C, M and T₁ filters of the Washington system and photoelectric CMT₁T₂ photometry of 20 red giant candidates. Based on the best fits of isochrones computed by the Geneva and Padova groups to the (V, V-I) colour-magnitude diagram, we derive a colour excess E(V-I) = 0.75, a cluster distance of 3.2 kpc and an age of 400 Myr. Five independent Washington abundance indices yield a mean cluster metallicity of [Fe/H]=-0.27 +/- 0.06, which is compatible with the existence of both a radial and Z gradient in the Galactic disc. NGC 2194 is a relatively young open cluster, whose deficiency in metal content can be accounted for by the fact that it was born not only far from the Galactic centre in the outer disc, but also at a relatively high Z value. ER - TY - Journal T1 - Integrated spectral evolution of Galactic open clusters A1 - Piatti, Andrés E. A1 - Bica, Eduardo A1 - Clariá, Juan J. A1 - Santos, João F. C. A1 - Ahumada, Andrea V. JO - Monthly Notices of the Royal Astronomical Society VL - 335 Y1 - 2002/9/1 SP - 233 EP - 240 KW - techniques: spectroscopic/ open cluster and associations: general/ galaxies: individual: Milky Way/ galaxies: star clusters UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.335..233P&db_key=AST&high=42a068d47501468 N2 - We present a library of 47 open-cluster integrated spectra, mostly obtained at CASLEO (San Juan, Argentina) in the range 3600 < lambda < 7400 Å, which are made available at CDS. The data are combined with previous spectra to obtain 10 high signal-to-noise ratio basic templates in the young and intermediate-age domains, which are also provided in the library. These Galactic disc templates represent the increased time resolution spectral evolution of a stellar population unit around the Solar metallicity level. The improved signal-to-noise ratio of the present templates with respect to previous template lists, together with their increased time resolution, allowed us to improve the fundamental parameters of some open clusters. The present spectral library will be useful for several astrophysical applications, particularly for population syntheses of star-forming giant galaxies. ER - TY - Journal T1 - Two highly reddened young open clusters located beyond the Sagittarius arm A1 - Piatti, A. E. A1 - Clariá, J. J. JO - Astronomy and Astrophysics VL - 388 Y1 - 2002/6/1 SP - 179 EP - 188 KW - open clusters and associations: individual: Pismis 23/ BH 222/ open clusters and associations: general/ techniques: photometric UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...388..179P&db_key=AST&high=42a068d47501468 N2 - We present the results of CCD BVI Johnson-Cousins photometry down to V ~ 19 mag in the regions of the unstudied stellar groups Pismis 23 and BH 222, both projected close to the direction towards the Galactic centre. We measured V magnitude and B-V and V-I colours for a total of 928 stars in fields of about 4arcmin x4arcmin . Pismis 23 is conclusively a physical system, since a clear main sequence and other meaningful features can be seen in the colour-magnitude diagrams. The reality of this cluster is also supported by star counts carried out within and outside the cluster field. For Pismis 23 we derive colour excesses E(B-V) = 2.0 +/- 0.1 and E(V-I) = 2.6 +/- 0.1, a distance from the Sun of 2.6 +/- 0.6 kpc (Z = -19 pc) and an age of 300 +/- 100 Myr (assuming solar metal content). BH 222 appears to be a young open cluster formed by a vertical main sequence and by a conspicuous group of luminous, typically red supergiant stars. We derived for this cluster a colour excess of E(V-I) = 2.4 +/- 0.2, a distance from the Sun of 6.0 +/- 2.7 kpc (Z = -46 pc) and an age of 60 +/- 30 Myr. The resulting reddening and distance estimates place these two young objects among the most reddened and distant open clusters known in the direction towards the Galactic centre. They are located beyond the Sagittarius arm, close to the direction where this arm probably bifurcates into two arms. Based on observations made at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile. Tables \ref{t2} and 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/179 ER - TY - Journal T1 - A revision of the fundamental parameters of the open cluster Hogg 15 and the projected star WR 47 A1 - Piatti, A. E. A1 - Bica, E. A1 - Santos, J. F. C., Jr. A1 - Clariá, J. J. JO - Astronomy and Astrophysics VL - 387 Y1 - 2002/5/1 SP - 108 EP - 116 KW - techniques: photometric/ techniques: spectroscopic/ galaxy: open clusters and associations: general/ galaxy: open clusters and associations: individual: Hogg 15/ stars: individual: WR UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...387..108P&db_key=AST&high=42a068d47501468 N2 - We revise the fundamental parameters of the faint open cluster Hogg 15, for which two recent colour-magnitude diagram (CMD) studies have obtained significantly different ages. In the present study, we combine a series of methods trying to constrain age, together with other fundamental parameters. We employ spatial extractions to construct the CMDs, and the cluster integrated spectrum to compare it with those of templates of known age. We derive fundamental parameters, in particular, distance, of the closely projected Wolf-Rayet star HDE 311884 (WR 47) - often proposed to be physically related to Hogg 15. Based on the WR 47 spectrum and available photometry, we conclude that the short distance implied by the Hipparcos parallax (216 pc) is affected by binary motion. From the WR 47 spectrum we estimate a reddening E(B-V) and a distance of 1.10 +/- 0.05 and 5.2 +/- 0.9 kpc, respectively. For Hogg 15 we derive an age of 20 +/- 10 Myr, a reddening of 1.10 +/- 0.05, and a distance of 3.1 +/- 0.5 kpc. We conclude that Hogg 15 is not related to WR 47 from the point of view of origin, since the cluster and the star do not belong to the same formation event. ER - TY - Journal T1 - Constraining the LMC cluster age gap: Washington photometry of NGC 2155 and SL 896 (LW 480) A1 - Piatti, Andrés E. A1 - Sarajedini, Ata A1 - Geisler, Doug A1 - Bica, Eduardo A1 - Clariá, Juan J. JO - Monthly Notices of the Royal Astronomical Society VL - 329 Y1 - 2002/1/1 SP - 556 EP - 566 KW - TECHNIQUES: PHOTOMETRIC/ GALAXIES: INDIVIDUAL: LMC/ MAGELLANIC CLOUDS/ GALAXIES: STAR CLUSTERS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.329..556P&db_key=AST&high=42a068d47501468 N2 - We carried out Washington system photometry of the intermediate-age Large Magellanic Cloud (LMC) star clusters NGC2155 and SL896 (LW480). We derive ages and metallicities from the T₁ versus C-T₁ colour-magnitude diagrams (CMDs). For the first time an age has been obtained for SL896, 2.3+/-0.5Gyr. For NGC2155 we derive 3.6+/-0.7Gyr. The two clusters basically define the lower age limit of the LMC age gap. In particular, NGC2155 is confirmed as the oldest intermediate-age LMC cluster so far studied. The derived metallicities are [Fe/H]=-0.9+/-0.2 and -0.6+/-0.2 for NGC2155 and SL896, respectively. We also studied the CMDs of the surrounding fields, which have a dominant turn-off comparable to that of the clusters themselves, and similar metallicity, showing that one is dealing with an intermediate-age disc where clusters and field stars have the same origin. We inserted the present clusters in the LMC and Small Magellanic Cloud (SMC) age-metallicity relations, using a set of homogeneous determinations with the same method as in our previous studies, now totalling 15 LMC clusters and four SMC clusters, together with some additional values from the literature. The LMC and SMC age-metallicity relations appear to be remarkably complementary, since the SMC was actively star-forming during the LMC quiescent age gap epoch. ER - TY - Journal T1 - On the nature of five open cluster candidates projected close to the Galactic centre A1 - Piatti, A. E. A1 - Clariá, J. J. JO - Astronomy and Astrophysics VL - 379 Y1 - 2001/11/1 SP - 453 EP - 460 KW - OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: RUPRECHT 103/ 124/ 129/ 146/ AND 166/ OPEN CLUSTERS AND ASSOCIATIONS : GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...379..453P&db_key=AST&high=42a068d47501468 N2 - We present CCD BVI observations obtained for 1759 stars in 4arcmin x4arcmin regions around the unstudied southern stellar aggregates Ruprecht 103, 124, 129, 146 and 166, which are described as open clusters in several catalogues. Our analysis shows that none of these stellar groups are genuine open clusters since no clear main sequences or other meaningful features can be seen in their colour-magnitude diagrams. Star counts carried out within and outside the cluster candidate fields not only support these results but also show that the studied objects do not appear to be candidate late stages of star cluster dynamical evolution. Based on observations made at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile. Tables 2 to 6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/453 ER - TY - Journal T1 - Ages and metallicities of five intermediate-age star clusters projected towards the Small Magellanic Cloud A1 - Piatti, Andrés E. A1 - Santos, João F. C. A1 - Clariá, Juan J. A1 - Bica, Eduardo A1 - Sarajedini, Ata A1 - Geisler, Doug JO - Monthly Notices of the Royal Astronomical Society VL - 325 Y1 - 2001/8/1 SP - 792 EP - 802 KW - TECHNIQUES: PHOTOMETRIC/ MAGELLANIC CLOUDS/ GALAXIES: STAR CLUSTERS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.325..792P&db_key=AST&high=42a068d47501468 N2 - Colour-magnitude diagrams are presented for the first time for L32, L38, K28 (L43), K44 (L68) and L116, which are clusters projected on to the outer parts of the Small Magellanic Cloud (SMC). The photometry was carried out in the Washington system C and T₁ filters, allowing the determination of ages by means of the magnitude difference between the red giant clump and the main-sequence turn-off, and metallicities from the red giant branch locus. The clusters have ages in the range 2-6Gyr, and metallicities in the range -1.65<[Fe/H]<-1.10, increasing the sample of intermediate-age clusters in the SMC. L116, the outermost cluster projected on to the SMC, is a foreground cluster, and somewhat closer to us than the Large Magellanic Cloud. Our results, combined with those for other clusters in the literature, show epochs of sudden chemical enrichment in the age-metallicity plane, which favour a bursting star formation history as opposed to a continuous one for the SMC. ER - TY - Journal T1 - On the stellar content of the open clusters Melotte 105, Hogg 15, Pismis 21 and Ruprecht 140 A1 - Piatti, A. E. A1 - Clariá, J. J. JO - Astronomy and Astrophysics VL - 370 Y1 - 2001/5/1 SP - 931 EP - 938 KW - OPEN CLUSTERS: INDIVIDUAL: MELOTTE 105/ HOGG 15/ PISMIS 21/ RUPRECHT 140/ OPEN CLUSTERS: GENERAL/ TECHNIQUES: PHOTOMETRIC UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...370..931P&db_key=AST&high=42a068d47501468 N2 - CCD observations in the B, V and I passbands have been used to generate colour-magnitude diagrams reaching down to V ~ 19 mag for two slightly characterized (Melotte 105 and Hogg 15) and two almost unstudied (Pismis 21 and Ruprecht 140) open clusters. The sample consists of about 1300 stars observed in fields of about 4arcmin x4arcmin . Our analysis shows that neither Pismis 21 nor Ruprecht 140 are genuine open clusters since no clear main sequences or other meaningful features can be seen in their colour-magnitude diagrams. Melotte 105 and Hogg 15 are open clusters affected by E(B-V) = 0.42 +/- 0.03 and 0.95 +/- 0.05, respectively. Their distances to the Sun have been estimated as 2.2 +/- 0.3 and 2.6 +/- 0.08 kpc, respectively, while the corresponding ages estimated from empirical isochrones fitted to the Main Sequence cluster members are ~ 350 Myr and 300 Myr, respectively. The present data are not consistent with the membership of the WN6 star HDE 311884 to Hogg 15. Tables 2 to 5 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.793.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/370/931 ER - TY - Journal T1 - BVI photometry and integrated spectroscopy of the very young open clusters Ruprecht 119, NGC 6318 and BH 245 A1 - Piatti, A. E. A1 - Bica, E. A1 - Clariá, J. J. JO - Astronomy and Astrophysics VL - 362 Y1 - 2000/10/1 SP - 959 EP - 967 KW - TECHNIQUES: PHOTOMETRIC/ TECHNIQUES: SPECTROSCOPIC/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: BH 245/ NGC 6318/ RUPRECHT 119 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...362..959P&db_key=AST&high=42a068d47501468 N2 - We present CCD BVI observations obtained for stars in the fields of the unstudied or poorly studied open clusters Ruprecht 119, NGC 6318, and BH 245 projected close to the direction towards the Galactic centre. We measured V magnitude and B-V and V-I colours for about 600 stars reaching down to V ~ 19 mag. From the analysis of the colour magnitude diagrams, we confirmed the physical reality of the clusters and derived their reddening, distance and age for the first time. In addition, we obtained flux-calibrated integrated spectra in the range 3500-9200 Å for the cluster sample. Using the equivalent widths of the Balmer lines and comparing the cluster spectra with template spectra we derive both foreground reddening and age. The photometric and spectroscopic results reveal that the three studied objects are very young open clusters with ages ranging between 10 and 15 Myr, which have already undergone the HII region evolutionary phase and are dominated by the upper MS stars. The clusters, located between 1.1 kpc and 3.3 kpc from the Sun, are affected by different amounts of interstellar visual absorption (2.4 <= A_v <= 7.0). In particular, BH 245 turned out to be a highly reddened open cluster located at a distance of scarcely 1.1 kpc. Based on observations made at the University of Toronto (David Dunlap Observatory) 24inch telescope, Las Campanas, Chile, and at the Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnics de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan, Argentina. ER - TY - Journal T1 - Photometric and integrated spectral study of the young open clusters Pismis 22, NGC 6178, NGC 6216 and Ruprecht 130 A1 - Piatti, A. E. A1 - Clariá, J. J. A1 - Bica, E. JO - Astronomy and Astrophysics VL - 360 Y1 - 2000/8/1 SP - 529 EP - 538 KW - GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 6178/ NGC 6216/ PISMIS 22/ RUPRECHT 130 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...360..529P&db_key=AST&high=42a068d47501468 N2 - We present CCD observations in the B, V , and I passbands obtained for stars in the fields of the open clusters Pismis 22, NGC 6178, NGC 6216, and Ruprecht 130, projected not far from the Galactic centre (|l| < 30Ì‚, |b| < 2Ì‚). The sample consists of about 790 stars reaching down to V ~ 18-19 mag. From the analysis of the colour magnitude diagrams, we confirmed the physical reality of the clusters and derived their reddening, distance and age. In addition, we obtained flux-calibrated integrated spectra in the range 3500-9200 Å for the cluster sample. The equivalent widths of the Balmer lines provided us with age estimates, while the comparison with template spectra allowed us to derive both foreground reddening and age. The photometric and spectroscopic results reveal that the four studied objects are young open clusters with ages ranging between 35 and 50 Myr. The clusters, located between 1.0 kpc and 4.3 kpc from the Sun, are affected by different amounts of interstellar visual absorption (0.6 ≃ A_v ≃ 6.0). Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la Repúbica Argentina and the National Universities of La Plata, Córdoba, and San Juan, Argentina, and at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile. Tables 3-6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - A New Giant Branch Clump Structure in the Large Magellanic Cloud A1 - Piatti, Andrés E. A1 - Geisler, Doug A1 - Bica, Eduardo A1 - Clariá, Juan J. A1 - Santos, João F. C., Jr. A1 - Sarajedini, Ata A1 - Dottori, Horacio JO - Astronomical Journal VL - 118 Y1 - 1999/12/1 SP - 2865 EP - 2874 KW - GALAXIES: INDIVIDUAL (LARGE MAGELLANIC CLOUD/ SMALL MAGELLANIC CLOUD)/ GALAXIES: PHOTOMETRY/ GALAXIES: STELLAR CONTENT UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....118.2865P&db_key=AST&high=42a068d47501468 N2 - We present Washington C and T₁ CCD photometry of 21 fields located in the northern part of the Large Magellanic Cloud (LMC), and spread over a region of more than 2.5 deg² approximately 6 deg from the bar. The surveyed areas were chosen on the basis of their proximity to SL 388 and SL 509, whose fields showed the presence of a secondary giant clump, observationally detected by Bica et al. We also observed NGC 2209, located ~14 deg away from SL 509. From the collected data, we found that most of the observed field CMDs do not show a separate secondary clump, but rather reveal a continuous vertical structure (VS), which is clearly seen for the first time. The VS also appears in the field of NGC 2209. Its position and size are nearly the same throughout the surveyed regions: it lies below the red giant clump (RGC) and extends from the bottom of the RGC to ~0.45 mag fainter, spanning the bluest color range of the RGC. In two fields in addition to the NGC 2209 field the RGC is slightly tilted, following approximately the reddening vector, while the VS maintains its verticality. We found that the number of stars in the VS box defined by Delta(C-T₁)=1.45-1.55 mag and DeltaT₁=18.75-19.15 mag has a strong spatial variation, reaching the highest VS star density just northeast of SL 509. Moreover, the more numerous the VS stars in a field, the larger the number of LMC giants in the same zone. We also found that, in addition to SL 509, two relatively massive star clusters, SL 515 and NGC 2209, separated by more than 10 deg from each other, develop giant clumps with a considerable number of VS stars. This result demonstrates that VS stars belong to the LMC and are most likely the result of some kind of evolutionary process in the LMC, particularly in those LMC regions with a noticeable large giant population. Our results are successfully predicted by the models of Girardi in the sense that a large proportion of 1-2 Gyr old stars mixed with older stars and with metallicities higher than [Fe/H]~=-0.7 should result in a fainter and bluer secondary clump near the mass at which degenerate core He burning takes place. However, our results apparently suggest that in order to trigger the formation of VS stars, there should be other conditions in addition to the appropriate age, metallicity, and the necessary red giant star density. Indeed, stars satisfying the requisites mentioned above are commonly found throughout the LMC, but the VS phenomenon is only clearly seen in some isolated regions. Finally, the fact that clump stars have an intrinsic luminosity dispersion further constrains the use of the clump magnitude as a reliable distance indicator. ER - TY - Journal T1 - Fundamental parameters of the moderately young open clusters NGC 5999, NGC 6031, Ruprecht 115 and Ruprecht 120 A1 - Piatti, Andres E. A1 - Claria, Juan J. A1 - Bica, Eduardo JO - Monthly Notices of the Royal Astronomical Society VL - 303 Y1 - 1999/2/1 SP - 65 EP - 76 KW - METHODS: OBSERVATIONAL/ OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 5999/ OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 6031/ OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: RUPRECHT 115/ OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: RUPRECHT 120 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.303...65P&db_key=AST&high=42a068d47501468 N2 - We present CCD BVI Johnson-Cousins photometry for the southern open clusters NGC 5999, NGC 6031, Ruprecht 115 and Ruprecht 120. The sample consists of about 1160 stars reaching down to V ~ 19 mag. From the analysis of the colour-magnitude diagrams, we confirm the reality of the clusters and derive their fundamental parameters (reddening, distance and age). We also present integrated spectra for NGC 6031, Ruprecht 115 and Ruprecht 120, covering a range from 3500 to 9200 A. From the equivalent widths of Balmer and infrared Ca ii triplet lines, as well as from a comparison of the obtained spectra with those of template clusters, we derive reddening, age and metallicity. The photometric and spectroscopic results allow us to conclude that the four clusters are moderately young (age &sim 100-500 Myr) and are located approximately towards the Galactic Centre at ~ 2.3 kpc from the Sun. NGC 6031 and Ruprecht 120 have nearly solar metal content, while Ruprecht 115 appears to be slightly metal-rich. ER - TY - Journal T1 - A Photometric and Spectroscopic Study of the Southern Open Clusters PISMIS 18, PISMIS 19, NGC 6005, and NGC 6253 A1 - Piatti, Andrés E. A1 - Clariá, Juan J. A1 - Bica, Eduardo A1 - Geisler, Doug A1 - Minniti, Dante JO - Astronomical Journal VL - 116 Y1 - 1998/8/1 SP - 801 EP - 812 KW - GALAXIES: STAR CLUSTERS/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NAME: PISMIS 18/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NAME: PISMIS 19/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC NUMBER: NGC 6005/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC NUMBER: NGC 6253 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116..801P&db_key=AST&high=42a068d47501468 N2 - CCD observations in the B, V, and I passbands have been used to generate color-magnitude diagrams (CMDs) for the southern open cluster candidates Pismis 18, Pismis 19, and NGC 6005, as well as for the old open cluster NGC 6253. The sample consists of about 1550 stars reaching down to V ~ 19 mag. From analysis of the CMDs, the physical reality of the three cluster candidates is confirmed and their reddening, distance, and age are derived, as well as those of NGC 6253. In addition, integrated spectra for Pismis 18, Pismis 19, and NGC 6253 covering a range from 3500 to 9200 Å were obtained. The reddening, age, and metallicity of these three clusters were derived from Balmer and Ca ii triplet equivalent widths by comparing the observed spectra with those of template clusters. The photometric and spectroscopic results allow us to conclude that Pismis 18, Pismis 19, and NGC 6005 are intermediate-age (t ~ 1 Gyr), genuine open clusters, while NGC 6253 has an age t ~ 5 Gyr. All these clusters are located approximately toward the Galactic center, between 1.5 and 2.7 kpc from the Sun. Their metallicities range over values that are typical of moderately metal-poor to moderately metal-rich open clusters. ER - TY - Journal T1 - Composite M V versus (V-I) 0 Diagram for Template Open Clusters A1 - Piatti, Andres E. A1 - Claria, Juan J. A1 - Bica, Eduardo JO - Astrophysical Journal Supplement Series VL - 116 Y1 - 1998/6/1 SP - 263 KW - STARS: HERTZSPRUNG-RUSSELL DIAGRAM/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL/ STARS: EVOLUTION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJS..116..263P&db_key=AST&high=42a068d47501468 N2 - New CCD VI photometric data for 10 template open clusters with accurately determined fundamental parameters are presented. From the observed V versus V - I diagrams of the clusters, fiducial sequences have been defined and transformed into the Mv versus (V - I)0 diagram by averaging sequences of template open clusters with similar ages. The resulting composite Mv versus (V - I)0 diagram presents a homogeneous set of empirical isochrones in the age range between 5 Myr and 4 Gyr. These empirical isochrones show an overall very good agreement with those computed from stellar evolutionary models. Theoretical isochrones with moderate overshooting fit the observed main sequences better than the canonical ones for clusters older than 600 Myr. The present set of empirical isochrones will be useful for the study of faint reddened open clusters ER - TY - Journal T1 - Fundamental parameters of the highly reddened young open clusters Westerlund 1 and 2 A1 - Piatti, A. E. A1 - Bica, E. A1 - Claria, J. J. JO - Astronomy and Astrophysics Supplement Series VL - 127 Y1 - 1998/2/1 SP - 423 EP - 432 KW - OPEN CLUSTERS: INDIVIDUAL: WESTERLUND1/ WESTERLUND2/ OPEN CLUSTERS: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..127..423P&db_key=AST&high=42a068d47501468 N2 - We study the compact open clusters Westerlund1 (BH197) and Westerlund2. We present CCD integrated spectroscopy for both clusters, and CCD imaging in the V and I bands for the former one. So far, Westerlund1 is possibly the most reddened open cluster studied in detail (A_v ~ 13.0). It has an age of 8 +/- 3 Myr and a distance from the Sun of d_sun ~ 1.0 +/- 0.4 kpc. For Westerlund2 we derive a visual absorption A_V~ 5.0 mag, an age of 2-3 Myr, and d_sun=5.7+/- 0.3 kpc. From luminosity and structural arguments we conclude that Westerlund1, although young and compact, it is a massive cluster, in contrast to Westerlund2. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina and the Universities of La Plata, Cordoba and San Juan, Argentina, and at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile. The photometric observations are available at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - Chemical Evolution of the Galactic Disk: Evidence for a Gradient Perpendicular to the Galactic Plane A1 - Piatti, Andres E. A1 - Claria, Juan J. A1 - Abadi, Mario G. JO - Astronomical Journal VL - 110 Y1 - 1995/12/1 SP - 2813 KW - GALAXY: EVOLUTION/ GALAXY: ABUNDANCES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995AJ....110.2813P&db_key=AST&high=42a068d47501468 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2813P&db_key=AST ER - TY - Journal T1 - Elemental abundance analyses with the EBASIM spectrograph of the 2.1-m CASLEO Observatory Telescope. I. The late B and early A stars vec xi Octantis, alpha Sextantis, and 68 Tauri A1 - Pintado, O. I. A1 - Adelman, S. J. JO - Astronomy and Astrophysics VL - 406 Y1 - 2003/8/1 SP - 987 EP - 994 KW - stars: abundances/ stars: individual: xi Oct/ stars: individual: alpha Sex/ stars: individual: 68 Tau/ stars: chemically peculiar UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...406..987P&db_key=AST&high=42a068d47504654 N2 - We used data from the EBASIM spectrograph of the 2.1-m CASLEO telescope to study three rather sharp-lined late B to early A stars xi Oct (B6 IV), alpha Sex (B9.5 III), and 68 Tau (A2 IV). These measurements are compared with those from the Anglo-Austrialian Telescope for the first star and to those from the coudé spectrograph of the 1.22-m telescope of the Dominion Astrophysical Observatory (DAO) for the other two stars. The equivalent width scales of the EBASIM and the DAO data are similar. Thus for the latter two stars the DAO data is also used in the analyses. Both xi Oct and alpha Sex generally have abundances close to those of the Sun in the range of values found for other normal stars with similar effective temperatures. The abundance pattern for 68 Tau is that of a metallic-lined star as is well known. Tables 5 to 7 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/406/987 ER - TY - Journal T1 - Elemental abundance analyses with Complejo Astronomico EL Leoncito REOSC echelle spectrograms. III. HR 4487, 14 Hydrae, and 3 Centauri A A1 - Pintado, O. I. A1 - Adelman, S. J. A1 - Gulliver, A. F. JO - Astronomy and Astrophysics Supplement Series VL - 129 Y1 - 1998/5/1 SP - 563 EP - 567 KW - STARS: ABUNDANCES/ STARS: CHEMICALLY PECULIAR/ STARS: INDIVIDUAL: HR 4487/ 14 HYA/ 3 CEN A UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26AS..129..563P&db_key=AST&high=42a068d47504654 N2 - Using CASLEO echelle spectrograms, elemental abundances are derived for the sharp-lined non-magnetic CP stars HR 4487, 14 Hya, and 3 Cen A. The first two stars are members of the Mercury-Manganese subgroup and have abundances which are similar to other such peculiar stars. The third is a hotter related star. The detection of Mn II lines in its spectrum adds to this relationship. Table 3 is avaible electronically vit the CDS via anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html. ER - TY - Journal T1 - Elemental abundance analyses with Complejo Astronomico. EL Leoncito REOSC echelle spectrograms. I. kappa Cancri, HR 7245, and xi Octantis A1 - Pintado, O. I. A1 - Adelman, S. J. JO - Astronomy and Astrophysics Supplement Series VL - 118 Y1 - 1996/8/1 SP - 283 EP - 291 KW - STARS: ABUNDANCES/ STARS: CHEMICALLY PECULIAR/ STARS: {KAPPA} CNC/ HR 7245/ {XI} OCT UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26AS..118..283P&db_key=AST&high=42a068d47504654 N2 - Elemental abundances are derived for three sharp-lined stars kappa Cnc, HR 7245, and xi Oct using REOSC echelle spectrograms obtained at CASLEO. Comparisons are made with published equivalent widths. The derived abundances for kappa Cnc and xi Oct are slightly larger than those obtained with other high dispersion spectrographs. HR 7245 exhibits a pattern of abundance anomalies similar to other Mercury-Manganese stars. The spectra of the two HgMn stars in the lambdalambda4640-5100 region exhibit an interesting and useful variety of lines which can be used to supplement analyses of the photographic region. ER - TY - Journal T1 - Application of Nonextensive Concepts that Include Fisher's Estimation Theory A1 - Plastino, A. A1 - Plastino, A. R. JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 287 EP - 298 KW - Fisher information/ non-extensivity/ Friedmann--Robertson--Walker cosmologies UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..287P&db_key=AST&high=42a068d47506158 N2 - We review some cosmological applications of nonextensivity in connection with Fisher's information measure in a nonextensive environment. ER - TY - Journal T1 - Foundations of Nonextensive Statistical Mechanics and Its Cosmological Applications A1 - Plastino, A. R. A1 - Plastino, A. R. A1 - Plastino, A. A1 - Miller, H. G. A1 - Uys, H. JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 275 EP - 286 KW - nonextensive statistical mechanics/ quantum distributions/ cosmology UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..275P&db_key=AST&high=42a068d47506158 N2 - The q-generalized quantum distributions, arising within the context of q-nonextensive thermostatistics, have recently found interesting applications to cosmology. These applications rest upon an approximated form of the q-distributions whose properties are not yet completely known. In order to shed some new light on this subject we consider here a maximum entropy principle leading to the q-generalized Fermi Dirac distribution. This variational principle is formulated entirely in terms of the mean occupation numbers. It constitutes a natural generalization to the nonextensive regime of the well-known prescription leading, in the standard q= 1 case, to the usual distribution for fermions. We analyze some important properties of this variational approach. In particular, we discuss 1) the invariance of the associated solutions under uniform shifts of the energy spectrum; 2) the role played by different kinds of constraints (i.e. linear or q-generalized constraints); and 3) the probabilistic interpretation of the variational procedure. The possibility of extending the present approach to bosons is also considered. ER - TY - Journal T1 - Tsallis Theory, the Maximum Entropy Principle, and Evolution Equations A1 - Plastino, A. R. JO - LNP Vol. 560: Nonextensive Statistical Mechanics and Its Application VL - 560 Y1 - 2001/1/1 SP - 157 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001LNP...560..157P&db_key=AST&high=42a068d47506158 N2 - Introduction Jaynes Maximum Entropy Principle General Thermostatistical Formalisms Time Dependent MaxEnt Time-Dependent Tsallis MaxEnt Solutions of the Nonlinear Fokker-Planck - Equation Tsallis Nonextensive Thermostatistics and the Vlasov-Poisson Equations Conclusions ER - TY - Journal T1 - Robe's Restricted Three-body Problem Revisited A1 - Plastino, A. R. A1 - Plastino, A. JO - Celestial Mechanics and Dynamical Astronomy VL - 61 Y1 - 1995/2/1 SP - 195 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995CeMDA..61..195P&db_key=AST&high=42a068d47506158 N2 - Not Available ER - TY - Journal T1 - Robe's Restricted Three-body Problem Revisited A1 - Plastino, A. R. A1 - Plastino, A. JO - Celestial Mechanics and Dynamical Astronomy VL - 61 Y1 - 1995/1/1 SP - 197 EP - 206 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995CeMDA..61..197P&db_key=AST&high=42a068d47506158 N2 - Not Available ER - TY - Journal T1 - The Gould Belt System and the Local Interstellar Medium A1 - Poppel, W. JO - Fundamentals of Cosmic Physics VL - 18 Y1 - 1997/1/1 SP - 1 EP - 271 KW - GOULD BELT/ LOCAL INTERSTELLAR MEDIUM/ SOLAR NEIGHBORHOOD/ SUPERSHELLS/ INTERSTELLAR PHASES/ DISK-HALO INTERACTIONS/ GOULD BELT/ LOCAL INTERSTELLAR MEDIUM/ SOLAR NEIGHBORHOOD/ SUPERSHELLS/ INTERSTELLAR PHASES/ DISK-HALO INTERACTIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997FCPh...18....1P&db_key=AST&high=42a068d47507234 N2 - The Gould belt (GB) system includes a flat local group of young stars and an associated interstellar (IS) superstructure of atomic and molecular gas. The distribution of the stars is tilted at about 18 deg to the galactic plane. The bulk of the gas is concentrated at |b| ~30 deg, with fainter extensions toward higher |b|. The total mass of the gas is near to 2 x 106 M? . Current evidences suggest that the stars and most of the gas are in expansion. The size of the GB system is of several hundred pc in the galactic plane. It could be considerably larger in the z-direction. On the other hand, a study of the global characteristics of all the IS medium in the solar neighborhood on a scale of several hundred pc makes apparent a very complex picture. Different phases are observed: cold and warm neutral media; warm and hot ionized media. Their spatial distributions and filling factors are not well known in detail. At low |b| there are large nearby molecular cloud complexes, while smaller fainter molecular clouds are found also at high |b|. HI-cloud complexes of high and intermediate velocities appear to be involved as well. Very striking distribution asymmetries between both galactic hemispheres are apparent in some of the local gas components. Furthermore, it seems well established that the Sun is located in a region of both low IS volume and surface density (perpendicular to the galactic plane). The role of the local IS magnetic field is not clear. The singular characteristics of the local IS medium appear to be closely related to the GB system. Two scenarios have been suggested for understanding at least some of the main observational facts: one is based on the occurrence of an explosive event; the other one considers one or more collisions of high velocity clouds with the galactic disk. The first scenario tries to explain the observed expansion and asymmetries but considers a previously existing tilted gas layer. The second scenario is able to explain the existence of large gaseous layers tilted to the galactic plane, but so far does not deal with all the observed characteristics of the local IS medium. Thus, even a combined scenario is conceivable, where a former collision of a large high velocity cloud complex with the disk produces the adequate conditions for the ulterior occurrence of an explosive event at large scale. ER - TY - Journal T1 - The spectroscopic orbits and the geometrical configuration of the symbiotic binary AR Pavonis A1 - Quiroga, C. A1 - Mikolajewska, J. A1 - Brandi, E. A1 - Ferrer, O. A1 - García, L. JO - Astronomy and Astrophysics VL - 387 Y1 - 2002/5/1 SP - 139 EP - 150 KW - stars: binaries: eclipsing/ stars: binaries: symbiotic/ stars: fundamental parameters/ stars: individual: AR Pav UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...387..139Q&db_key=AST&high=42a068d47511143 N2 - We analyze optical and near infrared spectra of intermediate and high resolution of the eclipsing symbiotic system AR Pavonis. We have obtained the radial velocity curves for the red and the hot component from the M-giant absorption lines and from the wings of Halpha , Hbeta and He II lambda 4686 emission profiles, respectively. From the orbital elements we have derived the masses, M_g=2.5 M_sun and M_h=1.0 M_sun, for the red giant and the hot component, respectively. We also present and discuss radial velocity patterns in the blue cF absorption spectrum as well as various emission lines. In particular, we confirm that the blue absorption lines are associated with the hot component. The radial velocity curve of the blue absorption system, however, does not track the hot companion's orbital motion in a straightforward way, and its departures from an expected circular orbit are particularly strong when the hot component is active. We suggest that the cF-type absorption system is formed in material streaming from the giant presumably in a region where the stream encounters an accretion disk or an extended envelope around the hot component. The broad emission wings originate from the inner accretion disk or the envelope around the hot star. We also suggest that the central absorption in H profiles is formed in a neutral portion of the cool giant's wind which is strongly concentrated towards the orbital plane. The nebula in AR Pav seems to be bounded by significant amount of neutral material in the orbital plane. The forbidden emission lines are probably formed in low density ionized regions extended in polar directions and/or the wind-wind interaction zone. Based on observations taken at Complejo Astronómico El Leoncito (CASLEO), operated under an agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, the Secretaría de Ciencia y Tecnología de la Nación and the National Universities of La Plata, Córdoba and San Juan. ER - TY - Journal T1 - Influence of the Neutron Star 1E 161348-5055 in RCW 103 on the Surrounding Medium A1 - Reynoso, E. M. A1 - Green, A. J. A1 - Johnston, S. A1 - Goss, W. M. A1 - Dubner, G. M. A1 - Giacani, E. B. JO - Publications of the Astronomical Society of Australia VL - 21 Y1 - 2004/1/1 SP - 82 EP - 88 KW - stars: neutron/ supernova remnants/ ISM: individual: RCW 103/ X-rays: individual: 1E 161348-5055/ spectral lines: neutral hydrogen. UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004PASA...21...82R&db_key=AST&high=42a068d47522324 N2 - We have carried out a study of the neutral hydrogen in the direction of the X-ray source 1E 161348-5055, a compact central object (CCO) located in the interior of the supernova remnant (SNR) RCW 103. The HI 21cm line observations were carried out using the Australia Telescope Compact Array, complemented with single dish data from the Parkes radio telescope to recover information at all spatial scales. We derive a distance to RCW 103 of 3.1kpc, in agreement with previous distance measurements. We have also detected a small hole in the HI emission which is positionally and kinematically coincident with the location of the CCO which confirms the association between the SNR and the CCO. This is the third case of a depression in HI emission seemingly associated with CCOs in SNRs. The characteristic parameters of the holes such as their size, eccentricity and evacuated mass are similar in all three cases. We estimate the absorbing HI column density towards 1E 161348-5055 to be ~6×10²¹cm^-2, a value compatible with a blackbody solution for the CCO X-ray emission. However, the implied temperature and luminosity are very high compared to most neutron stars. Moreover, the strong long-term variability in X-rays favours the hypothesis that 1E 161348-5055 is an accreting binary source rather than an isolated, cooling neutron star. An analysis of the continuum image obtained at 1.4GHz from these observations shows no trace of a pulsar wind nebula around 1E 161348-5055, in spite of it being a young object. ER - TY - Journal T1 - Observations of the neutral hydrogen surrounding the radio-quiet neutron star RX J0822-4300 in Puppis A A1 - Reynoso, E. M. A1 - Green, A. J. A1 - Johnston, S. A1 - Dubner, G. M. A1 - Giacani, E. B. A1 - Goss, W. M. JO - Monthly Notices of the Royal Astronomical Society VL - 345 Y1 - 2003/10/1 SP - 671 EP - 677 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.345..671R&db_key=AST&high=42a068d47522324 N2 - We have observed the HI distribution in an area 40 × 40 arcmin² around the neutron star candidate RX J0822-4300, which is located in the supernova remnant Puppis A. The observations of the lambda21-cm line were obtained with the Australia Telescope Compact Array and were combined with single-dish data from the Southern Galactic Plane Survey. The spatial resolution is 90 arcsec, and the velocity resolution is 1 km s^-1. A sensitivity of ~0.7 K was achieved. The results revealed a double-lobed feature of reduced emission at +16 km s^-1, centred on the central compact object (CCO), and aligned with an HI hole blueshifted by 13 km s^-1. The HI depressions have probably been created by the sweeping up of ~2 M_solar. The alignment between the lobes and the optical expansion centre of Puppis A suggests that the CCO could be ejecting two opposite jets. The velocity at which the two lobes are best defined has allowed us to confirm that the distance to Puppis A is 2.2 kpc, based on a systemic velocity of +16 km s^-1 . The hydrogen column density computed using this systemic velocity is consistent with estimates from models for X-ray spectra, thus reinforcing our conclusion that the kinematic distance is 2.2 kpc. ER - TY - Journal T1 - Very Large Array Observations of 6 Centimeter H₂CO in the Direction of Cassiopeia A A1 - Reynoso, E. M. A1 - Goss, W. M. JO - Astrophysical Journal VL - 575 Y1 - 2002/8/1 SP - 871 EP - 885 KW - ISM: Dust/ Extinction/ ISM: Clouds/ ISM: Individual: Name: Cassiopeia A/ ISM: Molecules/ ISM: Supernova Remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...575..871R&db_key=AST&high=42a068d47522324 N2 - H₂CO observations in the 1₁₀-1₁₁ transition (6 cm) obtained with the Very Large Array in the direction of the supernova remnant Cas A are presented. Absorption images are obtained with a resolution of 6" and a sensitivity of <~0.003. Molecular structures in the Perseus arm are observed between -34 and -49 km s^-1. The distribution of the molecular gas is significantly clumpy. Seventy-two clumps could be identified, with sizes of 0.17+/-0.05 pc, densities between 0.3 and 14×10⁴ cm^-3, and masses below 10 M_solar. In agreement with previous studies, most of the clumps, if not all, appear to be dispersing. The high H₂ column density to the west of Cas A accounts for the lack of optical emission in this region. Moreover, the optical extinction, estimated to be 8 mag toward the expansion center of Cas A, might explain why the supernova explosion was not observed in the 17th century. A major objective of the present survey is to search for signs of a possible interaction between Cas A and a western cloud. A striking correlation between the continuum emission and the H₂CO absorption distribution, and slight spectral broadenings toward the west, are the only evidence that may suggest that Cas A is interacting with an external cloud. However, the evidence is not enough to draw any definitive conclusion. ER - TY - Journal T1 - A Molecular Shell with Star Formation toward the Supernova Remnant G349.7+0.2 A1 - Reynoso, Estela M. A1 - Mangum, Jeffrey G. JO - Astronomical Journal VL - 121 Y1 - 2001/1/1 SP - 347 EP - 353 KW - ISM: Clouds- ISM: individual (G349.7+0.2)- ISM: Molecules- Stars: Formation- ISM: Supernova Remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121..347R&db_key=AST&high=42a068d47522324 N2 - A field of about 38'×38' around the supernova remnant (SNR) G349.7+0.2 has been surveyed in the CO J=1-0 transition with the 12 m telescope of the NRAO, using the on-the-fly technique. The resolution of the observations is 54^''. We have found that this remnant is interacting with a small CO cloud, which, in turn, is part of a much larger molecular complex, which we call the ``large CO shell.'' The large CO shell has a diameter of about 100 pc, an H₂ mass of 9.3×10⁵ M_solar, and a density of 35 cm^-3. We investigate the origin of this structure and suggest as a suitable hypothesis that an old supernova explosion occurred about 4×10⁶ yr ago. Analyzing the interaction between G349.7+0.2 and the large CO shell, it is possible to determine that the shock front currently driven into the molecular gas is a nondissociative shock (C-type), in agreement with the presence of OH 1720 MHz masers. The positional and kinematic coincidence of one of the CO clouds that constitute the large CO shell, an IRAS pointlike source, and an ultracompact H II region indicates the presence of a recently formed star. We suggest that the formation of this star was triggered during the expansion of the large CO shell and suggest the possibility that the same expansion also created the progenitor star of G349.7+0.2. The large CO shell would then be one of the few observational examples of supernova-induced star formation. ER - TY - Journal T1 - CO Observations toward Supernova Remnants with Associated OH 1720 MHZ Masers A1 - Reynoso, Estela M. A1 - Mangum, Jeffrey G. JO - Astrophysical Journal VL - 545 Y1 - 2000/12/1 SP - 874 EP - 884 KW - ISM: Clouds/ ISM: individual (G349.7+0.2/ CTB 37A)/ ISM: Individual: Alphanumeric: G16.7+0.1/ ISM: Molecules/ Masers/ ISM: Supernova Remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...545..874R&db_key=AST&high=42a068d47522324 N2 - The environs of three supernova remnants (SNRs) with associated OH 1720 MHz masers, G349.7+0.2, CTB 37A, and G16.7+0.1, have been surveyed in the CO J=1-0 transition with the 12 Meter Telescope of the NRAO, using the on-the-fly technique. These observations have revealed a number of molecular clouds interacting with the SNR shock fronts. Most of the OH 1720 MHz masers have been found to lie over CO concentrations, and the maser velocities are coincident with the CO peak velocities to an accuracy better than 2 km s^-1. The present data trace the interstellar medium (ISM) structures interacting with the SNRs; however, to probe the shocked molecular gas in which the OH 1720 MHz emission originates, higher excitation transitions and more complex species should be observed. In CTB 37A, where the shock velocity into the molecular cloud could be determined, it has been found to be of C-type, in agreement with theoretical predictions. Part of the rim of G16.7+0.1 appears to be flattened by a dense external cloud, yet the only associated OH 1720 MHz maser lies near the opposite region of the remnant. This behavior, also observed in IC 443 and 3C 391, seems to contradict the suggestion that OH 1720 MHz maser emission occurs mainly for transverse shocks. ER - TY - Journal T1 - A New Determination of the Distance to Kepler's Supernova Remnant A1 - Reynoso, E. M. A1 - Goss, W. M. JO - Astronomical Journal VL - 118 Y1 - 1999/8/1 SP - 926 EP - 929 KW - ISM: CLOUDS/ ISM: H I/ ISM: INDIVIDUAL (3C 358=KEPLER'S SUPERNOVA/ ISM: SUPERNOVA REMNANTS/ SUPERNOVAE: INDIVIDUAL (SN 1604) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....118..926R&db_key=AST&high=42a068d47522324 N2 - Using the Very Large Array, H I observations of Kepler's supernova remnant (SN 1604, 3C 358) have been carried out with an angular resolution of approximately 15" and a velocity resolution of 1.3 km s^-1. The distance to this historical supernova remnant (SNR diameter~3') has been controversial, with estimates ranging from a few kiloparsecs to 12 kpc. Based on a weak H I absorption feature at +21.3 km s^-1 seen in the new data, a lower limit of 4.8+/-1.4 kpc can be derived. No prominent interstellar H I features are detected near Kepler's SNR, indicating that the evolution of the remnant has been influenced by the circumstellar medium, while the interstellar medium seems to have had negligible effect on the expansion process. At a velocity of +21.3 km s^-1, emission from an H I cloud to the east of the SNR is detected, which may be physically associated with the remnant of SN 1604, based on morphological considerations. An upper limit of 6.4 kpc to the distance can be derived based on the lack of H I absorption at a velocity of +50 km s^-1, where extended H I emission is detected. ER - TY - Journal T1 - The Environs of Tycho's Supernova Remnant Explored through the H I 21 Centimeter Line A1 - Reynoso, E. M. A1 - Velázquez, P. F. A1 - Dubner, G. M. A1 - Goss, W. M. JO - Astronomical Journal VL - 117 Y1 - 1999/4/1 SP - 1827 EP - 1833 KW - ISM: CLOUDS/ ISM: H I/ ISM: INDIVIDUAL (3C 10=TYCHO'S SUPERNOVA)/ SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....117.1827R&db_key=AST&high=42a068d47522324 N2 - The detection of high-density H I that is very likely to be interacting with Tycho's supernova remnant (SNR) is reported. The interstellar medium around the remnant was surveyed using high-resolution (~13") VLA archive observations in the 21 cm line of neutral hydrogen. We have found cold, dense gas at kinematic velocities compatible with the SNR, in excellent agreement with the locations where, based on earlier proper-motion expansion studies of the synchrotron emission, the shock front is expanding more slowly than most of the SNR shell. The site of lowest expansion velocity along the whole shell is coincident with a small H I clump observed as an absorption feature at v=-51.5 km s^-1, with a density in the range 160-325 cm^-3. The clump seems to have been intercepted by the shock front in the recent past and has not yet undergone significant evaporation. Toward the western side of the SNR shell, which morphologically preserves spherical symmetry and expands at a higher rate, no H I features have been observed. We conclude that the presence of dense concentrations toward the east is currently slowing down the expansion of the shock front locally. These observations demonstrate that the properties of the local interstellar medium can affect the dynamical evolution of SNRs even at early stages. ER - TY - Journal T1 - A VLA Study of the Expansion of Tycho's Supernova Remnant A1 - Reynoso, E. M. A1 - Moffett, D. A. A1 - Goss, W. M. A1 - Dubner, G. M. A1 - Dickel, J. R. A1 - Reynolds, S. P. A1 - Giacani, E. B. JO - Astrophysical Journal VL - 491 Y1 - 1997/12/1 SP - 816 KW - ISM: INDIVIDUAL NAME: TYCHO'S SUPERNOVA/ ISM: INDIVIDUAL ALPHANUMERIC: 3C 10/ ISM: KINEMATICS AND DYNAMICS/ ISM: SUPERNOVA REMNANTS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...491..816R&db_key=AST&high=42a068d47522324 N2 - We have measured the expansion of Tycho's supernova remnant (SNR) over a 10 yr interval by comparing new VLA observations at 1375 MHz made in 1994 and 1995 with previous observations made in 1983 and 1984 using the same array configurations, bandwidths, calibrators, and integration times. To compute the expansion of the outer rim, we estimate the expansion rate for radial sectors of 4 deg. The overall mean expansion obtained is 3."05 but varies between 1" and 5" around the shell. The weighted average fractional expansion rate is 0.1126% yr-1, corresponding to a power-law index (expansion parameter) nu = d ln R/d ln t = 0.471, with an error of ~6%. We also compute the expansion of interior features, and find a comparable global expansion parameter. The value of nu obtained is in excess of the pure Sedov value of 0.4, indicating that Tycho's SNR is still in transition from an earlier phase to the Sedov adiabatic phase of evolution, and supporting expansion into a medium without a strong radial density gradient, as expected for a Type Ia supernova. In addition, the significant local variations that we observe suggest that a unique average expansion rate is an oversimplified description for Tycho. Both radio flux and polarization were found to remain almost constant during the intervening 10 years. ER - TY - Journal T1 - Cold neutral gas associated with the GUM nebula A1 - Reynoso, E. M. A1 - Dubner, G. M. JO - Astronomy and Astrophysics Supplement Series VL - 123 Y1 - 1997/5/1 SP - 31 EP - 41 KW - ISM: SUPERNOVA REMNANTS/ ISM: INDIVIDUAL OBJECTS: GUM NEBULA/ ISM: BUBBLES/ RADIO LINES: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26AS..123...31R&db_key=AST&high=42a068d47522324 N2 - Based on HI maps covering the 3600 square degrees area delimited by 230 deg <= l <= 290 deg, -30 deg <= b <= 30 deg, we investigated the neutral hydrogen distribution in the Gum nebula and its environments. The main result is the appearence of a huge disk of neutral gas at a kinematical distance compatible with that of the nebula, and whose angular dimensions coincide with the optical image of the Gum nebula. The disk, roughly centered at l ~= 262 deg, b~= -3 deg, is located at ~500 pc and has a radius of ~150 pc. We propose that this HI disk is the neutral gas component of the optical nebula, hence becoming the first time in which a structure with the dimensions of the optical nebula is detected in other wavelengths. We analyze the fitting of observations with different theoretical models and conclude that the most plausible interpretation is that the Gum nebula is a supershell produced by the action of repeated SN explosions, where the explosions may have originated in the aged association Vela OB2. In this context, the thick HI shell shown by \cite[Dubner \e \ (1992)]{ref14} near (266 deg, -2.5 deg) and the Vela SNR are the debris of two of the several outbursts which started in the region about 6 x 10^6 years ago. The southern boundary is distorted due to the presence of a ~28 deg radius shell, which appears to be an interstellar bubble driven by the stellar winds of the O--type star HD 49798. ER - TY - Journal T1 - Neutral hydrogen compact absorption features in Cassiopeia A. A1 - Reynoso, E. M. A1 - Goss, W. M. A1 - Dubner, G. M. A1 - Winkler, P. F. A1 - Schwarz, U. J. JO - Astronomy and Astrophysics VL - 317 Y1 - 1997/1/1 SP - 203 EP - 211 KW - ISM: SUPERNOVA REMNANTS/ ISM: INDIVIDUAL: CAS A/ STARS: MASS LOSS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...317..203R&db_key=AST&high=42a068d47522324 N2 - Very Large Array (VLA) observations of the lambda21 cm H I line towards Cassiopeia A (Cas A) have been performed. The velocity interval observed was from -38 to -362(LSR)km/s, with a resolution of 2.6km/s and a beam size of 14.2"x11.4". Opacity images show the presence of a number of small absorption H I features in the velocity interval -62 to -69km/s (LSR) which, on the basis of several arguments, are postulated to be physically associated with Cas A. These cold H I knots have sizes of <0.1pc and show spatial substructure. Their velocities lie well outside the range of the intervening H I in the Perseus spiral arm, i.e. 0 to -55km/s. We demonstrate that the H I knots cannot be described as shocked interstellar cloudlets engulfed by the blast wave of the supernova remnant (SNR). Instead, we propose that these low velocity H I features are recombined wind driven clumps moving ahead of the supernova (SN) shock front. This hypothesis is supported by the ages derived for the knots, varying from 8x10^3^ to 5x10^4^years, which implies that these features were originally accelerated during the Wolf-Rayet (WR) phase of the precursor star. ER - TY - Journal T1 - VLA Observations of Neutral Hydrogen in the Direction of Puppis A A1 - Reynoso, E. M. A1 - Dubner, G. M. A1 - Goss, W. M. A1 - Arnal, E. M. JO - Astronomical Journal VL - 110 Y1 - 1995/7/1 SP - 318 KW - SUPERNOVA REMNANTS/ ISM: ABUNDANCES/ ISM: KINEMATICS AND DYNAMICS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995AJ....110..318R&db_key=AST&high=42a068d47522324 N2 - Abstract image available at: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110..318R&db_key=AST ER - TY - Journal T1 - A kinetic model for rotating diluted gaseous envelopes in a central field A1 - Rohrmann, Rene D. JO - Monthly Notices of the Royal Astronomical Society VL - 285 Y1 - 1997/2/1 SP - 427 EP - 438 KW - CIRCUMSTELLAR MATTER/ STARS: EARLY-TYPE/ STARS: ROTATION. UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997MNRAS.285..427R&db_key=AST&high=42a068d47524900 N2 - A model based on the kinetic theory is proposed for tenuous gaseous envelopes subject to a central attraction field. Quasi- steady states are studied where the gaseous system shows differential rotation. The particle density, the gas mean velocity and the kinetic temperature are analytically determined. The model predicts two possible configurations of gas distribution: normal envelope and shell, which can be defined in terms of relevant physical parameters, such as the intensity of the field and the angular velocity of the inner region of the system. The kinematic behaviour of the gas is analysed in detail by studying the hydrodynamic limit of the rotationally forced ejection of matter and the condition of escape. The importance of thermal wind in the external region of the envelope is considered. ER - TY - Journal T1 - The Binary Black Hole Scenario for the BL Lacertae Object AO~0235+16 A1 - Romero, G. E. A1 - Fan, Jun-Hui A1 - Nuza, S. E. JO - Chinese Journal of Astronony and Astrophysics VL - 3 Y1 - 2003/12/1 SP - 513 EP - 525 KW - galaxies: active/ BL Lacertae objects: individual: AO 0235+16/ gamma rays: theory/ black hole physics UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ChJAA...3..513R&db_key=AST&high=42a068d47529508 N2 - Recent analysis of the long term radio light curve of the extremely variable BL Lacertae object AO 0235+16 by Raiteri et al. have revealed the presence of recurrent outbursts with a period of ~ 5.7± 0.5 yr. Periodicity analysis of the optical light curve also shows evidence for a shorter period. Here we discuss whether such a behavior can be explained by a binary black hole model where the accretion disk of one of the supermassive black holes is precessing due to the tidal effects of the companion. We estimate the mass of the accreting hole and analyze constraints on the secondary mass and the orbital parameters of the system. It is possible to provide a viable interpretation of the available multiwavelength data. ER - TY - Journal T1 - Hadronic gamma-ray emission from windy microquasars A1 - Romero, G. E. A1 - Torres, D. F. A1 - Kaufman Bernadó, M. M. A1 - Mirabel, I. F. JO - Astronomy and Astrophysics VL - 410 Y1 - 2003/10/1 SP - L1 EP - L4 KW - X-rays: binaries/ stars/ gamma-rays: observations/ gamma-rays: theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...410L...1R&db_key=AST&high=42a068d47529508 N2 - The jets of microquasars with high-mass stellar companions are exposed to the dense matter field of the stellar wind. We present estimates of the gamma-ray emission expected from the jet-wind hadronic interaction and we discuss the detectability of the phenomenon at high energies. The proposed mechanism could explain some of the unidentified gamma-ray sources detected by EGRET instrument on the galactic plane. ER - TY - Journal T1 - Signatures of Hadronic Cosmic Rays in Starbursts? High-Energy Photons and Neutrinos from NGC 253 A1 - Romero, Gustavo E. A1 - Torres, Diego F. JO - Astrophysical Journal VL - 586 Y1 - 2003/3/1 SP - L33 EP - L36 KW - Galaxies: Individual: NGC Number: NGC 253/ Galaxies: Starburst/ Gamma Rays: Observations/ Gamma Rays: Theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...586L..33R&db_key=AST&high=42a068d47529508 N2 - We show that it appears possible for starburst galaxies, like the nearby NGC 253, recently identified as a TeV source by the CANGAROO collaboration, to emit a significant amount of high-energy gamma-rays and neutrinos through hadronic processes in their cores. We suggest that proton illumination of the inner winds of massive stars can be a viable mechanism for producing TeV gamma-rays and neutrinos without a strong MeV-GeV counterpart. The rich stellar content of the starbursts, with millions of early-type stars concentrated in the central regions, where collective effects of the stellar winds and supernovae can produce a significant enhancement of the cosmic-ray density, provides an adequate scenario for TeV gamma-ray generation. Close starbursts are also found to be potential sources for kilometer-scale neutrino telescopes, like IceCube, within reasonable integration times. ER - TY - Journal T1 - Recurrent microblazar activity in Cygnus X-1? A1 - Romero, G. E. A1 - Kaufman Bernadó, M. M. A1 - Mirabel, I. F. JO - Astronomy and Astrophysics VL - 393 Y1 - 2002/10/1 SP - L61 EP - L64 KW - X-ray binaries/ stars: individual: Cyg X-1/ gamma-rays: observations/ gamma-rays: theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...393L..61R&db_key=AST&high=42a068d47529508 N2 - Recurrent flaring events at X- and soft gamma-ray energies have been recently reported for the galactic black hole candidate Cygnus X-1. The observed fluxes during these transient outbursts are far higher than what is observed in ``normal'' episodes. Here we suggest that the origin of this radiation is non-thermal and produced by inverse Compton interactions between relativistic electrons in the jet and external photon fields, with a dominant contribution from the companion star field. The recurrent and relatively rapid variability could be explained by the precession of the jet, which results in a variable Doppler amplification. ER - TY - Journal T1 - Optical microvariability of EGRET blazars A1 - Romero, G. E. A1 - Cellone, S. A. A1 - Combi, J. A. A1 - Andruchow, I. JO - Astronomy and Astrophysics VL - 390 Y1 - 2002/8/1 SP - 431 EP - 438 KW - galaxies: active/ galaxies: photometry/ BL Lacertae objects: general/ gamma-rays: observations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...390..431R&db_key=AST&high=42a068d47529508 N2 - We present results of a photometric CCD study of the incidence of microvariability in the optical emission of a sample of 20 blazars detected at gamma-ray energies by the EGRET instrument of the Compton Gamma-Ray Observatory. We have observed strong outbursts in some sources, but many others displayed no significant variability on timescales of hours. The typical minimum timescale is found to be of ~ several hours, not tens of minutes as claimed by some authors. The duty cycle for optical intranight microvariations of gamma-ray blazars, as estimated from our observations, seems to be ~ 50%, lower than what is usually assumed. For night-to-night variations, instead, the duty cycle approaches that observed in radio-selected BL Lacs and flat-spectrum radio quasars (i.e. ~ 70%). Based on observations made at the Complejo Astronómico El Leoncito, which is operated under agreement between CONICET and the National Universities of La Plata, Córdoba, and San Juan. Table \ref{t_stars} is only available in electronic form at http://www.edpsciences.org ER - TY - Journal T1 - Variable gamma-ray emission from the Be/X-ray transient A0535+26? A1 - Romero, G. E. A1 - Kaufman Bernadó, M. M. A1 - Combi, J. A. A1 - Torres, D. F. JO - Astronomy and Astrophysics VL - 376 Y1 - 2001/9/1 SP - 599 EP - 605 KW - X-RAYS: STARS/ GAMMA-RAYS: THEORY/ RADIO CONTINUUM: OBSERVATIONS/ STARS: INDIVIDUAL: A0535+26/ STARS: NEUTRON UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...376..599R&db_key=AST&high=42a068d47529508 N2 - We present a study of the unidentified gamma-ray source 3EG J0542+2610. This source is spatially superposed on the supernova remnant G180.0-1.7, but its time variability makes a physical link unlikely. We have searched in the EGRET location error box for compact radio sources that could be the low energy counterpart of the gamma-ray source. Although 29 point-like radio sources were detected and measured, none of them is strong enough to be considered the counterpart of a background gamma-ray emitting AGN. We suggest that the only object within the 95% error box capable of producing the required gamma-ray flux is the X-ray transient A0535+26. We show that this Be/accreting pulsar can produce variable hadronic gamma-ray emission through the mechanism originally proposed by Cheng & Ruderman (1989), where a proton beam accelerated in a magnetospheric electrostatic gap impacts the transient accretion disk. ER - TY - Journal T1 - Two-Color Photometry with High Temporal Resolution of the Extremely Variable Blazar PKS 0537-441 A1 - Romero, Gustavo E. A1 - Cellone, Sergio A. A1 - Combi, Jorge A. JO - Astronomical Journal VL - 120 Y1 - 2000/9/1 SP - 1192 EP - 1197 KW - BL Lacertae objects: individual (PKS 0537-441)/ Galaxies: Active/ Galaxies: Photometry UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....120.1192R&db_key=AST&high=42a068d47529508 N2 - We report the results of a microvariability monitoring campaign on the southern blazar PKS 0537-441. The source was observed in the V and R optical bands throughout six consecutive nights. Strong variations at both bands, with amplitudes of ~0.3 mag, were observed on timescales of about 2 days. Smaller fluctuations of ~0.05 mag on a scale of a couple of hours are superposed on the larger outburst. The spectral index was also variable during the observing period, with an average value of alpha=-1.6 and changes up to ~27.5%. The spectrum varies in the sense that it becomes harder when the source is brighter, in accordance with predictions of shock-in-jet models. We discuss our results and the possible origin of the variability in this blazar in light of recent higher frequency observations. ER - TY - Journal T1 - Extreme intranight variability in the BL Lacertae object AO 0235+164 A1 - Romero, G. E. A1 - Cellone, S. A. A1 - Combi, J. A. JO - Astronomy and Astrophysics VL - 360 Y1 - 2000/8/1 SP - L47 EP - L50 KW - GALAXIES: BL LACERTAE OBJECTS: INDIVIDUAL: AO 0235+164/ GALAXIES: PHOTOMETRY/ RADIATION MECHANISMS: NON-THERMAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...360L..47R&db_key=AST&high=42a068d47529508 N2 - We present results of two-colour photometry with high time resolution of the violently variable BL Lac object AO 0235+164. We have found extreme intranight variability with amplitudes of ~ 100% over time scales of 24 hours. Changes of 0.5 magnitudes in both R and V bands were measured within a single night, and variations up to 1.2 magnitudes occurred from night to night. A complete outburst with an amplitude ~ 30% was observed during one of the nights, while the spectrum remained unchanged. This seems to support an origin based on a thin relativistic shock propagating in such a way that it changes the viewing angle, as recently suggested by Kraus et al. (1999) and Qian et al. (2000). ER - TY - Journal T1 - Beaming and precession in the inner jet of 3C 273 --- II. The central engine A1 - Romero, G. E. A1 - Chajet, L. A1 - Abraham, Z. A1 - Fan, J. H. JO - Astronomy and Astrophysics VL - 360 Y1 - 2000/8/1 SP - 57 EP - 64 KW - GALAXIES: QUASARS: INDIVIDUAL: 3C 273/ GAMMA RAYS: THEORY/ BLACK HOLE PHYSICS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...360...57R&db_key=AST&high=42a068d47529508 N2 - The quasar 3C 273 is a well-known superluminal source. More than 10 radio components have been detected moving away from the nucleus with different superluminal speeds and position angles. The pattern of ejection suggests the existence of a precessing inner jet, whose kinematics has been discussed by Abraham & Romero (1999). We now present a binary black hole model for the central engine of 3C 273 where the rapid precession is tidally induced in the primary accretion disk inner region by a secondary black hole in a non-coplanar orbit. Using gamma- and X-ray data we estimate upper limits for the mass of the primary, and then we compute the relevant parameters of the system for a variety of disk models. We also discuss some of the implications of the model for the electromagnetic and gravitational radiation from 3C 273. ER - TY - Journal T1 - Gamma-ray bursts with peculiar temporal asymmetry A1 - Romero, Gustavo E. A1 - Torres, Diego F. A1 - Andruchow, I. A1 - Anchordoqui, Luis A. A1 - Link, Bennett JO - Monthly Notices of the Royal Astronomical Society VL - 308 Y1 - 1999/9/1 SP - 799 EP - 806 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999MNRAS.308..799R&db_key=AST&high=42a068d47529508 N2 - Based on Link & Epstein's study of temporal asymmetry of 631 gamma-ray bursts from the BATSE 3B catalogue, we identify the population of bursts with rising times that are longer than their decays, thus showing atypical profiles. We analyse their sky distribution, morphology, time-space clustering and other average properties and compare them with those associated with the bulk of the bursts. We show how most of the peculiar bursts analysed are consistent with recent fireball models, but a fraction of bursts (~4per cent of the total sample) appear to be inconsistent. ER - TY - Journal T1 - Unidentified 3EG gamma-ray sources at low galactic latitudes A1 - Romero, G. E. A1 - Benaglia, P. A1 - Torres, D. F. JO - Astronomy and Astrophysics VL - 348 Y1 - 1999/8/1 SP - 868 EP - 876 KW - GAMMA RAYS: OBSERVATIONS/ STARS: EARLY-TYPE/ ISM: SUPERNOVA REMNANTS/ STARS: PULSARS: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...348..868R&db_key=AST&high=42a068d47529508 N2 - We present a study on the possible association of unidentified gamma -ray sources in the Third EGRET (3EG) catalog with different types of galactic objects such as Wolf-Rayet and Of stars, supernova remnants (SNRs), and OB associations (considered as pulsar tracers). We have made use of numerical simulations of galactic populations of gamma -ray point sources in order to determine the statistical significance of the positional coincidences. New constraints on pure chance association are presented for SNRs and OB associations. There is overwhelming statistical support for the hypothesis that some SNRs are gamma -ray sources (we obtain probabilities of pure chance association <10(-5) ). OB star associations present higher, but still negligible probabilities (<10(-3) ). It is also shown that although massive stars present just marginally significant correlation with 3EG sources, there is a posteriori support for at least three candidates. ER - TY - Journal T1 - Optical microvariability of southern AGNs A1 - Romero, G. E. A1 - Cellone, S. A. A1 - Combi, J. A. JO - Astronomy and Astrophysics Supplement Series VL - 135 Y1 - 1999/3/1 SP - 477 EP - 486 KW - GALAXIES: ACTIVE/ BL LACERTAE OBJECTS: GENERAL/ QUASARS: GENERAL/ GALAXIES: PHOTOMETRY UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26AS..135..477R&db_key=AST&high=42a068d47529508 N2 - We present results of a search for optical microvariability in a selected sample of 23 southern AGNs, which includes both radio-quiet and radio-loud objects. Microvariations were clearly detected in 60% of the radio-loud sources, with amplitudes from 2.2% up to 8% within a single night. Night-to-night variability with amplitudes of ~ 20% was also observed in the BL Lac object 0537-441. On the contrary, no rapid variability was detected at all in 8 radio-quiet quasars. We have used microvariability data previously reported for northern objects along with our new results for southern AGNs in order to estimate duty cycles of each class of objects from the largest possible sample. Most of the microvariability in radio-loud objects could be originating in interactions between relativistic shocks and features in the inner jets, although contributions from superluminal microlensing and accretion disk instabilities can be present in some sources. It is possible that the latter phenomenon is responsible for the microvariability observed in northern radio-quiet quasars. We suggest that the difference in the microvariability behaviour of radio and X-ray selected BL Lacs could be due to the effect of stronger magnetic fields in the latter group of objects, fields that can prevent the formation of features like density inhomogeneities and bends in the base of the jets by Kelvin-Helmholtz macroscopic instabilities. Figures 1.2 to 1.23 are only available in the electronic version at http://www.edpsciences.com ER - TY - Journal T1 - Search for intraday radio variability in EGRET blazars. A1 - Romero, G. E. A1 - Combi, J. A. A1 - Benaglia, P. A1 - Azcarate, I. N. A1 - Cersosimo, J. C. A1 - Wilkes, L. M. JO - Astronomy and Astrophysics VL - 326 Y1 - 1997/10/1 SP - 77 EP - 86 KW - RADIO CONTINUUM: GALAXIES/ GALAXIES: ACTIVE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...326...77R&db_key=AST&high=42a068d47529508 N2 - We present results of intraday variability observations at 5 GHz of the EGRET blazars 0202+14, 0235+16, 2230+11, and 2251+15. The BL-Lac object 0235+16 presented flux density variations of ~7% over timescales of ~1.3days. The source 0202+14 was also variable, although with smaller amplitudes. The behaviour of 0235+16 at short timescales is almost identical to that presented in previous intraday observations carried out in 1990, when the flux density of the source was 4 times higher. We discuss the possible origin of the ultra rapid radio variability in these sources within different possible scenarios. ER - TY - Journal T1 - Variability observations of selected southern extragalactic radio sources A1 - Romero, G. E. A1 - Benaglia, P. A1 - Combi, J. A. JO - Astronomy and Astrophysics Supplement Series VL - 124 Y1 - 1997/8/1 SP - 307 EP - 313 KW - GALAXIES: ACTIVE/ RADIO CONTINUUM: GALAXIES/ GALAXIES: NGC 5128/ QUASARS: PKS 1610-771; PKS 1830-211 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26AS..124..307R&db_key=AST&high=42a068d47529508 N2 - Results of variability observations of the southern extragalactic radio sources PKS 1610-771, PKS 1830-211 and the inner region of Centaurus A (Cen A) at 1.42 GHz are presented. Different light curves with temporal resolutions of ~30 minutes, 1 day and 1 month were obtained for each source. Significant variability was detected in PKS 1610-771 and Cen A. The implications of these results are discussed. ER - TY - Journal T1 - Rapid variability of southern extragalactic radio sources A1 - Romero, G. E. A1 - Benaglia, P. A1 - Combi, J. A. JO - Journal of Astronomical Data VL - 3 Y1 - 1997/1/1 SP - 2 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997JAD.....3....2R&db_key=AST&high=42a068d47529508 N2 - Results of short-term variability observations at 1.4 GHz of southern active galactic nuclei are presented. The data were obtained in three different campaigns with a 30 m single dish telescope located in Argentina. The data set corresponding to the first campaign includes polarization information. Residual values are also given for all observations. ER - TY - Journal T1 - Centaurus A as a source of extragalactic cosmic rays with arrival energies well beyond the GZK cutoff A1 - Romero, Gustavo E. A1 - Combi, Jorge A. A1 - Perez Bergliaffa, Santiago E. A1 - Anchordoqui, Luis A. JO - Astroparticle Physics VL - 5 Y1 - 1996/10/1 SP - 279 EP - 283 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996APh.....5..279R&db_key=AST&high=42a068d47529508 N2 - The ultra-high energy cosmic rays recently detected by several air shower experiments could have an extragalactic origin. In this case, the nearest active galaxy Centaurus A might be the source of the most energetic particles ever detected on Earth. We have used recent radio observations in order to estimate the arrival energy of the protons accelerated by strong shock fronts in the outer parts of this southern radio source. We expect detections corresponding to particles with energies up to ~2.2 x10^21 eV and an arrival direction of (l ~310^o, b ~20^o) in galactic coordinates. The future Southern Hemisphere Pierre Auger Observatory might provide a decisive test for extragalactic models of the origin of the ultra-high energy cosmic rays. ER - TY - Journal T1 - A model for the soft gamma-ray variability in MeV blazars. A1 - Romero, G. E. JO - Astronomy and Astrophysics VL - 313 Y1 - 1996/9/1 SP - 759 EP - 767 KW - QUASARS: GENERAL/ QUASARS: INDIVIDUAL: 3C 273/ SHOCK WAVES/ GAMMA RAYS: THEORY UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...313..759R&db_key=AST&high=42a068d47529508 N2 - Recent observations with the COMPTEL instrument on the Compton Gamma Ray Observatory (CGRO) have revealed that several blazar-type sources present a strong peak in the 0.75-8.0 MeV range of their emission. Moreover, at least four of these objects have displayed variability in the soft gamma-ray flux over timescales of months. In this paper I present a model for such variability based on the interaction of a strong relativistic shock with density inhomogeneities in the inner pair beam of these sources. The shock increases the soft gamma-emission by compression of the particle density and the consequent enhancement of the blue-shifted annihilation radiation. The shocked particles also emit synchrotron radiation producing simultaneous or quasi-simultaneous outbursts at lower frequencies. This model is applied to the well-studied quasar 3C 273, a source for which multifrequency temporal observations are available. ER - TY - Journal T1 - Fine-Scale Structure in Relativistic Jets and Rapid Variability in Blazars A1 - Romero, G. E. JO - Astrophysics and Space Science VL - 234 Y1 - 1995/12/1 SP - 49 EP - 55 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Ap%26SS.234...49R&db_key=AST&high=42a068d47529508 N2 - Not Available ER - TY - Journal T1 - Rapid radio variability in PKS 0537-441: superluminal microlensing caused by small masses in a foreground galaxy? A1 - Romero, G. E. A1 - Surpi, G. A1 - Vucetich, H. JO - Astronomy and Astrophysics VL - 301 Y1 - 1995/9/1 SP - 641 KW - GRAVITATIONAL LENSING/ DARK MATTER/ BL LACERTAE OBJECTS: INDIVIDUAL: PKS 0537-441/ RADIO CONTINUUM: GALAXIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...301..641R&db_key=AST&high=42a068d47529508 N2 - The southern blazar PKS 0537-441 has recently displayed very strong intraday variability at 1.42GHz. Flux density variations with amplitudes of ~45% on time scales as short as 10^4^s were registered, implicating brightness temperatures higher than 10^21^K in a straightforward intrinsic interpretation. We suggest and discuss the possibility that this variability have an extrinsic origin based on gravitational microlensing by small compact objects (namely brown dwarfs) in a foreground galaxy. In the proposed model the variability arises when a superluminal emission knot in the jet of the blazar is lensed by objects of the dark halo of the intervening galaxy. For an emission region with a superluminal velocity beta_app_~10 in the lens plane, the masses of the lenses are in the 10^-4^-10^-3^M_sun_ range. From the event rate we have estimated a dark matter density 0.009<~rho_o_<~0.043hM_sun_/pc^3^ in the center of the foreground galaxy. ER - TY - Journal T1 - Flicker of southern extragalactic radio sources at 1.42 GHz. A1 - Romero, G. E. A1 - Benaglia, P. A1 - Combi, J. A. JO - Astronomy and Astrophysics VL - 301 Y1 - 1995/9/1 SP - 33 KW - BL LACERTAE OBJECTS/ QUASARS/ GALAXIES: ACTIVE/ RADIO CONTINUUM: GALAXIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...301...33R&db_key=AST&high=42a068d47529508 N2 - Variability of southern extragalactic radio sources on time scales of 1-10 days has been studied at 1.42GHz using a 30-m telescope with a declination range from -9deg to -90deg. Measurements of 18 sources were made in 11 successive nights in each of two observing sessions. Most of the flat-spectrum sources vary a few percent on time scales mainly in the range 2-4 days, a behaviour that could be originated, or at least strongly influenced, by refractive processes in the interstellar medium. A few sources displayed a higher level of activity with rms fluctuations of ~6%. This latter variability could be partially intrinsic to the sources. ER - TY - Journal T1 - Variability in the Southern blazars PKS 1921-293 and PKS 2155-152 A1 - Romero, G. E. A1 - Combi, J. A. JO - Astrophysics and Space Science VL - 229 Y1 - 1995/7/1 SP - 23 EP - 32 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Ap%26SS.229...23R&db_key=AST&high=42a068d47529508 N2 - Not Available ER - TY - Journal T1 - Rapid Variability in the Southern Blazar PKS 0521-365 A1 - Romero, G. E. A1 - Combi, J. A. A1 - Vucetich, H. JO - Astrophysics and Space Science VL - 225 Y1 - 1995/3/1 SP - 183 EP - 204 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995Ap%26SS.225..183R&db_key=AST&high=42a068d47529508 N2 - Not Available ER - TY - Journal T1 - Calibration of the Whipple atmospheric Caronerenkov telescope A1 - Rovero, A. C. A1 - Buckley, J. H. A1 - Fleury, P. A1 - Jiang, Y. A1 - Pare, E. A1 - Sarazin, X. A1 - Urban, M. A1 - Weekes, T. C. JO - Astroparticle Physics VL - 5 Y1 - 1996/6/1 SP - 27 EP - 34 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996APh.....5...27R&db_key=AST&high=42a068d47501528 N2 - Caronerenkov ring images from single muons have been used to calibrate the Whipple Observatory 10 m imaging telescope. This approach tests the total throughput of the telescope and uses a known atmospheric Caronerenkov light signal that closely matches the spectrum of the atmospheric Caronerenkov signal from an air-shower. The absolute calibration is derived by matching the observed ring images with those predicted by a simple geometrical and physical model; a value of 1.25+/-0.13 photoelectrons equivalent to 1 digital count was found. Using this value simulations indicate that the telescope had an energy threshold of 300 GeV when this calibration was made. ER - TY - Journal T1 - Current Perspectives of Astronomy in Argentina A1 - Rovira, M. G. JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 247 EP - 257 KW - astronomy/ Argentinean observatories/ Argentinean institutes UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..247R&db_key=AST&high=42a068d47502141 N2 - Not Available ER - TY - Journal T1 - Bright Points and Subflares in Ultraviolet Lines and X-Rays A1 - Rovira, M. A1 - Schmieder, B. A1 - Démoulin, P. A1 - Simnett, G. M. A1 - Hagyard, M. J. A1 - Reichmann, E. A1 - Tandberg-Hanssen, E. JO - Astrophysical Journal VL - 510 Y1 - 1999/1/1 SP - 474 EP - 484 KW - SUN: FLARES/ SUN: UV RADIATION/ SUN: X-RAYS/ GAMMA RAYS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...510..474R&db_key=AST&high=42a068d47502141 N2 - We have analyzed an active region which was observed in Halpha (Multichannel Subtractive Double Pass Spectrograph), in UV lines (SMM/UVSP), and in X-rays (SMM/HXIS). In this active region there were only a few subflares and many small bright points visible in UV and in X-rays. Using an extrapolation based on the Fourier transform, we have computed magnetic field lines connecting different photospheric magnetic polarities from ground-based magnetograms. Along the magnetic inversion lines we find two different zones: (1) a high-shear region (>70 deg) where subflares occur, and (2) a low-shear region along the magnetic inversion line where UV bright points are observed. In these latter regions the magnetic topology is complex with a mixture of polarities. According to the velocity field observed in the Si IV lambda1402 line and the extrapolation of the magnetic field, we notice that each UV bright point is consistent with emission from low-rising loops with downflows at both ends. We notice some hard X-ray emissions above the bright-point regions with temperatures up to 8 x 10^6 K, which suggests some induced reconnection due to continuous emergence of new flux. This reconnection is also enhanced by neighboring subflares. ER - TY - Journal T1 - A Spectrographic Study of the Interacting Eclipsing Binary RY Scuti: An Episode in the Rapid Mass Loss Stage or a Protoplanetary Nebula? A1 - Sahade, J. A1 - West, R. M. A1 - Skul'Sky, M. Yu. JO - Revista Mexicana de Astronomia y Astrofisica VL - 38 Y1 - 2002/10/1 SP - 259 EP - 274 KW - Binaries: Eclipsing/ Binaries/ individual: RY Scuti/ Protoplanetary Nebula UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002RMxAA..38..259S&db_key=AST&high=42a068d47503996 N2 - RY Scuti, the 11-day [Fe III] eclipsing binary, has been reinvestigated on the basis of spectrographic material obtained in Chile at the European Southern Observatory, La Silla, and at the Cerro Tololo Interamerican Observatory, covering the spectral regions 3400-5150 Å and 5700-6700 Å . Ultraviolet IUE observations were also analyzed. The spectrum of RY Sct is very complex and peculiar, being characterized by several sets of emission as well as absorption features. Among the emission features, there is a set of lines that are characteristic of planetary nebulae. The system is found to be formed by a B0V component and a companion that appears to be surrounded by an opaque envelope that emits in He II lambda 4686. In the circumbinary envelope we can distinguish: (a) a region of diluted radiation that suggests a velocity of ~ - 178 km s-1; (b) regions of formation of the resonance lines of Si IV and C IV in the IUE UV, characterized by velocities of -1200 and -600 km s-1; (c) regions that give rise to the ``nebular spectrum" and suggest that there is a triple nebulosity surrounding the system with N[e] probably larger than 10⁴ cm-3, T[e] ~ 15-20,000 K and velocities of -18, +9 and +48 km s-1, respectively. ER - TY - Journal T1 - The Interacting Eclipsing Binary AU Monocerotis Revisited A1 - Sahade, J. A1 - Ferrer, O. A1 - Garcia, L. G. A1 - Brandi, E. A1 - Barba, R. JO - Publications of the Astronomical Society of the Pacific VL - 109 Y1 - 1997/11/1 SP - 1237 EP - 1240 KW - BINARIES: ECLIPSING UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997PASP..109.1237S&db_key=AST&high=42a068d47503996 N2 - New spectrographic observations of the Algol binary AU Monocerotis have permitted the determination of the orbital elements of the two components of the system. They have further suggested that the image tube spectrograph that was attached to the CTIO 1m-reflecting telescope in 1978 and 1979 was not quite suitable for radial velocity work. (SECTION: Stars) ER - TY - Journal T1 - About the So-called Serpentid Stars A1 - Sahade, Jorge JO - Comments on Astrophysics VL - 18 Y1 - 1995/1/1 SP - 347 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ComAp..18..347S&db_key=AST&high=42a068d47503996 N2 - Not Available ER - TY - Journal T1 - On X-ray interacting binaries with no compact components. A1 - Sahade, J. JO - Comments on Astrophysics VL - 18 Y1 - 1995/1/1 SP - 161 EP - 166 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ComAp..18..161S&db_key=AST&high=42a068d47503996 N2 - Not Available ER - TY - Journal T1 - Anisotropy in the distribution of satellites around primary galaxies in the 2dF Galaxy Redshift Survey: the Holmberg effect A1 - Sales, Laura A1 - Lambas, Diego G. JO - Monthly Notices of the Royal Astronomical Society VL - 348 Y1 - 2004/3/1 SP - 1236 EP - 1240 KW - galaxies: evolution/ galaxies: formation/ cosmology: theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.348.1236S&db_key=AST&high=42a068d47504952 N2 - We have analysed a sample of satellite and primary galaxies in the 2dF Galaxy Redshift Survey. In our study we find strong statistical evidence of the Holmberg effect (that is, a tendency for satellites to avoid regions along the line defined by the primary plane) within 500 kpc of the projected distance to the primary. This effect is present only when we restrict our analysis to objects with radial velocity relative to the primary |Deltav| < 160 km s^-1, which corresponds approximately to the mean of the distribution. We explore the dependence of this anisotropy on spectral type (eta), colours and luminosities of both primaries and satellites, finding that objects with a low present-day star formation rate present the most significant effect. ER - TY - Journal T1 - Determination of the linear mass power spectrum from the mass function of galaxy clusters A1 - Sánchez, Ariel G. A1 - Padilla, Nelson D. A1 - Lambas, Diego G. JO - Monthly Notices of the Royal Astronomical Society VL - 337 Y1 - 2002/11/1 SP - 161 EP - 171 KW - cosmology: theory/ large-scale structure of Universe UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.337..161S&db_key=AST&high=42a068d47513999 N2 - We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation sigma(M) using the expression for the mass function in the Press & Schechter, Sheth, Mo & Tormen and Jenkins et al. formalisms. We apply different techniques to recover the adimensional power spectrum Delta²(k) from sigma(M) namely the k_eff approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the tauCDM and LambdaCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (FKP) method. We find that the mass function based method presented here can provide a very accurate estimate of the linear power spectrum, particularly for low values of k. This estimate is comparable to, or even better behaved than, the FKP solution. The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution. ER - TY - Journal T1 - Contraction of Radiating Shell in Classical and Post-Newtonian Approximation A1 - Santoro, Fernando A1 - Aquilano, Roberto A1 - Ibaceta, David JO - Astrophysics and Space Science VL - 268 Y1 - 1999/1/1 SP - 469 EP - 474 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999Ap%26SS.268..469S&db_key=AST&high=42a068d47515420 N2 - A semi-numeric method was used to study the evolution of a general-relativistic radiating shell in its Post-Newtonian and Newtonian approximations. The solutions, where the main parameters are given reasonable values, show that a relativistic effect can be found in X-ray-burster-like objects. ER - TY - Journal T1 - The effects of mergers on the formation of disc-bulge systems in hierarchical clustering scenarios A1 - Scannapieco, C. A1 - Tissera, P. B. JO - Monthly Notices of the Royal Astronomical Society VL - 338 Y1 - 2003/2/1 SP - 880 EP - 890 KW - methods: numerical/ galaxies: evolution/ galaxies: fundamental parameters/ galaxies: interactions UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.338..880S&db_key=AST&high=42a068d47517350 N2 - We study the effects of mergers on the structural properties of disc-like systems by using smooth particle hydrodynamical (SPH) numerical simulations in hierarchical clustering scenarios. In order to assess the effects of mergers on the mass distributions we performed a bulge-disc decomposition of the projected surface density of the systems at different stages of the merger process. We assumed an exponential law for the disc component and the Sérsic law for the bulges. We found that simulated objects at z= 0 have bulge profiles with shape parameters n~ 1, consistent with observational results of spiral galaxies. The complete sample of simulated objects at z= 0 and z > 0 shows that n takes values in the range n~ 0.4-4. We found that secular evolution tends to produce exponential bulge profiles, while the fusion of baryonic cores tends to increase the n value and helps to generate the correlation between B/D and n. We found no dependence on the relative mass of the colliding objects. Our results suggest that mergers, through secular evolution and fusions, could produce the transformation of galactic objects along the Hubble sequence by driving a morphological loop that might also depend on the properties of the central galactic potential wells, which are also affected by mergers. ER - TY - Journal T1 - The ages and colours of cool helium-core white dwarf stars A1 - Serenelli, A. M. A1 - Althaus, L. G. A1 - Rohrmann, R. D. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 325 Y1 - 2001/8/1 SP - 607 EP - 616 KW - STARS: ATMOSPHERES/ STARS: EVOLUTION/ STARS: FUNDAMENTAL PARAMETERS/ STARS: INTERIORS/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.325..607S&db_key=AST&high=42a068d47519556 N2 - The purpose of this work is to explore the evolution of helium-core white dwarf stars in a self-consistent way with the predictions of detailed non-grey model atmospheres and element diffusion. To this end, we consider helium-core white dwarf models with stellar masses of 0.406, 0.360, 0.327, 0.292, 0.242, 0.196 and 0.169M_solar and follow their evolution from the end of mass-loss episodes, during their pre-white dwarf evolution, down to very low surface luminosities. We find that when the effective temperature decreases below 4000K, the emergent spectrum of these stars becomes bluer within time-scales of astrophysical interest. In particular, we analyse the evolution of our models in the colour-colour and in the colour-magnitude diagrams and find that helium-core white dwarfs with masses ranging from ~0.18 to 0.3M_solar can reach the turn-off in their colours and become blue again within cooling times much less than 15Gyr and then remain brighter than M_V~16.5. In view of these results, many low-mass helium white dwarfs could have had enough time to evolve to the domain of collision-induced absorption from molecular hydrogen, showing blue colours. ER - TY - Journal T1 - The ages and colours of cool helium-core white dwarf stars A1 - Serenelli, A. M. A1 - Althaus, L. G. A1 - Rohrmann, R. D. A1 - Benvenuto, O. G. JO - Monthly Notices of the Royal Astronomical Society VL - 325 Y1 - 2001/8/1 SP - 607 EP - 616 KW - STARS: ATMOSPHERES/ STARS: EVOLUTION/ STARS: FUNDAMENTAL PARAMETERS/ STARS: INTERIORS/ WHITE DWARFS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.325..607S&db_key=AST&high=42a068d47524094 N2 - The purpose of this work is to explore the evolution of helium-core white dwarf stars in a self-consistent way with the predictions of detailed non-grey model atmospheres and element diffusion. To this end, we consider helium-core white dwarf models with stellar masses of 0.406, 0.360, 0.327, 0.292, 0.242, 0.196 and 0.169M_solar and follow their evolution from the end of mass-loss episodes, during their pre-white dwarf evolution, down to very low surface luminosities. We find that when the effective temperature decreases below 4000K, the emergent spectrum of these stars becomes bluer within time-scales of astrophysical interest. In particular, we analyse the evolution of our models in the colour-colour and in the colour-magnitude diagrams and find that helium-core white dwarfs with masses ranging from ~0.18 to 0.3M_solar can reach the turn-off in their colours and become blue again within cooling times much less than 15Gyr and then remain brighter than M_V~16.5. In view of these results, many low-mass helium white dwarfs could have had enough time to evolve to the domain of collision-induced absorption from molecular hydrogen, showing blue colours. ER - TY - Journal T1 - A wavelet packets equalization technique to reveal the multiple spatial-scale nature of coronal structures A1 - Stenborg, G. A1 - Cobelli, P. J. JO - Astronomy and Astrophysics VL - 398 Y1 - 2003/2/1 SP - 1185 EP - 1193 KW - methods: data analysis/ methods: numerical/ techniques: image processing/ Sun: corona/ Sun: coronal mass ejections (CMEs) UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...398.1185S&db_key=AST&high=42a068d47525640 N2 - Precise determination of onset times of dynamical events as observed by coronagraphs requires a high-degree-of-accuracy tracking of the structures involved. In particular, early steps in the evolution turn to be of utmost importance. However, corresponding features often lack the sharpness needed to obtain unambiguous results. To overcome this constraint, we developed a multiresolution image processing technique applicable to any coronagraph data set to enhance both boundaries and internal details of originally faint and diffuse structures. The method implemented employs a multi-level decomposition scheme (splitting algorithm of a wavelet packet on non-orthogonal wavelets) via the àtrous wavelet transform, local noise reduction and interactive weighted recomposition. This approach represents a major advance towards unambiguous image interpretation and provides a means for the quantification of stationary and dynamic coronal structures required for conducting morphological studies. A range of example applications based on LASCO-C1, -C2, and -C3 data sets are shown. Different reconstruction strategies are discussed. ER - TY - Journal T1 - MICA: The Mirror Coronagraph for Argentina A1 - Stenborg, G. A1 - Schwenn, R. A1 - Srivastava, N. A1 - Inhester, B. A1 - Podlipnik, B. A1 - Rovira, M. A1 - Francile, C. JO - Space Science Reviews VL - 87 Y1 - 1999/1/1 SP - 307 EP - 310 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999SSRv...87..307S&db_key=AST&high=42a068d47525640 N2 - As part of the new German-Argentinian Solar Observatory in El Leoncito, San Juan, Argentina, a new ground-based solar telescope (MICA) began to operate in August 1997. MICA is an advanced mirror coronagraph, its design being an almost exact copy of the LASCO-C1 instrument. Since its installation, it has been imaging the inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges corresponding to the emission lines of the Fe XIV and Fe X ions. The instrument can image the corona as fast as every minute. Thus, it is ideally suited to study fast processes in the inner corona. In this way, it is a good complement for the LASCO-C1 instrument. After a brief review of the instrument, we present some recent observations showing the capabilities of the instrument. ER - TY - Journal T1 - A radio continuum survey of the southern sky at 1420 MHz. Observations and data reduction A1 - Testori, J. C. A1 - Reich, P. A1 - Bava, J. A. A1 - Colomb, F. R. A1 - Hurrel, E. E. A1 - Larrarte, J. J. A1 - Reich, W. A1 - Sanz, A. J. JO - Astronomy and Astrophysics VL - 368 Y1 - 2001/3/1 SP - 1123 EP - 1132 KW - METHODS: OBSERVATIONAL/ SURVEYS/ GALAXY: GENERAL/ RADIO CONTINUUM: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...368.1123T&db_key=AST&high=42a068d47527413 N2 - We describe the equipment, observational method and reduction procedure of an absolutely calibrated radio continuum survey of the South Celestial Hemisphere at a frequency of 1420 MHz. These observations cover the area 0^h <= RA <= 24^h for declinations less than -10degr . The sensitivity is about 50 mK T_B (full beam brightness) and the angular resolution (HPBW) is 35farcm4 , which matches the existing northern sky survey at the same frequency. ER - TY - Journal T1 - Studying Galactic Chemical Properties by using Cosmological Numerical Simulations A1 - Tissera, Patricia B. A1 - Scannapieco, Cecilia JO - Publications of the Astronomical Society of Australia VL - 21 Y1 - 2004/1/1 SP - 192 EP - 196 KW - Galaxy: dynamical and chemical evolution/ methods: N-body simulations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004PASA...21..192T&db_key=AST&high=42a068d47527679 N2 - We developed a chemical code within GADGET2 which allows the description of the enrichment of the Universe as a function of redshift, taking into account detailed metal production by supernovae Ia and II, and metal-dependent cooling. This is the first numerical code that includes both chemical production and metal-dependent cooling in a cosmological context. By analysing the cosmic star formation rate, we found that the effects of considering a metal-dependent cooling are important, principally, for z <~ 3. In simulations where primordial cooling functions are used, the comoving star formation rate could be up to 20% lower than those obtained in runs with metal-dependent cooling functions. Within galaxy-like objects, the presence of chemical elements changes the star-formation rates and, consequently, the chemical production and patterns of stars. However, owing to non-linear evolution of the structure, the effects depend on the evolutionary history path of each galaxy-like object. ER - TY - Journal T1 - Nitrogen abundances in damped Lyman alpha systems: the combined effects of SNII and SNIa in a hierarchical clustering scenario A1 - Tissera, Patricia B. A1 - Lambas, Diego G. A1 - Cora, Sofia A. A1 - Mosconi, Mirta B. JO - Monthly Notices of the Royal Astronomical Society VL - 337 Y1 - 2002/12/1 SP - L27 EP - L30 KW - galaxies: abundances/ galaxies: evolution/ galaxies: formation/ cosmology: theory UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.337L..27T&db_key=AST&high=42a068d47527679 N2 - The combined enrichment of supernovae (SN) types II and I in a hierarchical clustering scenario could produce regions with low N content with respect to alpha elements, consistent with observed values measured in damped Lyman alpha systems (DLAs). We have studied the formation of DLAs in a hierarchical clustering scenario under the hypothesis that the building blocks of current field galaxies could be part of the structures mapped by DLAs. In our models the effects of the non-linear evolution of the structure (which produces bursty star formation histories, gas infall, etc.) and the contributions of SNIa and SNII are found to be responsible of producing these N regions with respect to the alpha elements. Although SNIa are not main production sites for Si or O, because of the particular timing between SNIa and SNII, their contributions can help to produce clouds with such abundances. Consistently, we found the simulated low nitrogen DLAs to have subsolar [Fe/H]. We show that low nitrogen DLAs have experienced important star formation activity in the past with higher efficiency than normal DLAs. Our chemical model suggests that SNIa play a relevant role in the determination of the abundance pattern of DLA and, that the observed low nitrogen DLA frequency could be explained taking into account the time-delay of ~0.5 Gyr introduced by these supernova to release metals. ER - TY - Journal T1 - Double starbursts triggered by mergers in hierarchical clustering scenarios A1 - Tissera, P. B. A1 - Domínguez-Tenreiro, R. A1 - Scannapieco, C. A1 - Sáiz, A. JO - Monthly Notices of the Royal Astronomical Society VL - 333 Y1 - 2002/6/1 SP - 327 EP - 338 KW - galaxies: evolution/ galaxies: formation/ galaxies: interactions/ cosmology: theory/ dark matter UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.333..327T&db_key=AST&high=42a068d47527679 N2 - We use cosmological smooth particle hydrodynamical (SPH) simulations to study the effects of mergers in the star formation history of galactic objects in hierarchical clustering scenarios. We find that during some merger events, gaseous discs can experience two starbursts: the first one during the orbital decay phase, owing to gas inflows driven as the satellite approaches, and the second one when the two baryonic clumps collide. A trend for these first induced starbursts to be more efficient at transforming the gas into stars is also found. We detect that systems that do not experience early gas inflows have well-formed stellar bulges and more concentrated potential wells, which seem to be responsible for preventing further gas inward transport triggered by tidal forces. The potential wells concentrate owing to the accumulation of baryons in the central regions and of dark matter as the result of the pulling in by baryons. The coupled evolution of the dark matter and baryons would lead to an evolutionary sequence during which systems with shallower total potential wells suffer early gas inflows during the orbital decay phase that help to feed their central mass concentration, pulling in dark matter and contributing to build up more stable systems. Within this scenario, starbursts triggered by early gas inflows are more likely to occur at early stages of evolution of the systems and to be an important contributor to the formation of stellar bulges. Our results constitute the first proof that bulges can form as the product of collapse, collisions and secular evolution in a cosmological framework, and they are consistent with a rejuvenation of the stellar population in bulges at intermediate z with, at least, 50 per cent of the stars (in SCDM) being formed at high z. ER - TY - Journal T1 - Chemical Enrichment at High Redshifts: Understanding the Nature of Damped Lyalpha Systems in Hierarchical Models A1 - Tissera, Patricia B. A1 - Lambas, Diego G. A1 - Mosconi, Mirta B. A1 - Cora, Sofia JO - Astrophysical Journal VL - 557 Y1 - 2001/8/1 SP - 527 EP - 532 KW - Cosmology: Theory/ Cosmology: Dark Matter/ Galaxies: Abundances/ Galaxies: Evolution/ Galaxies: Formation/ Methods: Numerical UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...557..527T&db_key=AST&high=42a068d47527679 N2 - We use cosmological hydrodynamical simulations including star formation and metal enrichment to study the evolution of the chemical properties of galaxy-like objects at high redshift in the range 0.25solar yr^-1) and a series of starbursts. We find that even the accretion of a small satellite can be correlated with a stellar burst. Massive mergers are found to be more efficient at transforming gas into stars ER - TY - Journal T1 - Dark matter halo structure in CDM hydrodynamical simulations A1 - Tissera, P. B. A1 - Dominguez-Tenreiro, R. JO - Monthly Notices of the Royal Astronomical Society VL - 297 Y1 - 1998/6/1 SP - 177 EP - 194 KW - HYDRODYNAMICS/ METHODS: NUMERICAL/ GALAXIES: EVOLUTION/ GALAXIES: FORMATION/ DARK MATTER UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998MNRAS.297..177T&db_key=AST&high=42a068d47527679 N2 - We have carried out a comparative analysis of the properties of dark matter haloes in N-body and hydrodynamical simulations. We analyse their density profiles, shapes and kinematical properties with the aim of assessing the effects that hydrodynamical processes might produce on the evolution of the dark matter component. The simulations performed allow us to reproduce dark matter haloes with high resolution, although the range of circular velocities is limited. We find that for haloes with circular velocities of [150-200] km s^-1 at the virial radius, the presence of baryons affects the evolution of the dark matter component in the central region, modifying the density profiles, shapes and velocity dispersions. We also analyse the rotation velocity curves of disc-like structures and compare them with observational results. ER - TY - Journal T1 - Analysis of galaxy formation with hydrodynamics A1 - Tissera, Patricia B. A1 - Lambas, Diego G. A1 - Abadi, Mario G. JO - Monthly Notices of the Royal Astronomical Society VL - 286 Y1 - 1997/4/1 SP - 384 EP - 392 KW - HYDRODYNAMICS/ SHOCK WAVES/ METHODS: NUMERICAL/ STARS: FORMATION/ GALAXIES: FORMATION/ DARK MATTER UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997MNRAS.286..384T&db_key=AST&high=42a068d47527679 N2 - We present a hydrodynamical code based on the smoothed particle hydrodynamics (SPH) technique implemented in an AP_3M code that is aimed at solving the hydrodynamical and gravitational equations in a cosmological frame. We analyse the ability of the code to reproduce standard tests and perform numerical simulations to study the formation of galaxies in a typical region of a cold dark matter (CDM) model. These numerical simulations include gas and dark matter particles and take into account physical processes such as shock waves, radiative cooling and a simplified model of star formation. We analyse the astrophysical properties of the galactic objects in different models. ER - TY - Journal T1 - Extinction Effects in Spiral Galaxy Rotation Curves A1 - Valotto, Carlos A1 - Giovanelli, Riccardo JO - Astronomical Journal VL - 128 Y1 - 2004/7/1 SP - 115 EP - 120 KW - ISM: Dust/ Extinction/ Galaxies: Fundamental Parameters/ Galaxies: Halos/ Galaxies: Spiral UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....128..115V&db_key=AST&high=42a068d47531540 N2 - Observations show that the slope of the inner part of the Halpha/[N II] rotation curve of disk galaxies is depressed by extinction: at fixed luminosity, the observed slope is in fact seen to depend on the disk inclination to the line of sight. Using a simple extinction model, we are able to reproduce well the observed trends. The model assumes an exponential distribution, both in the radial and z directions, identical for star-forming regions and dust. Fits to the data are optimized by varying the scale height and scale length of absorbers, as well as the disk's central optical depth tau₀, as seen face-on. The observations indicate that disk central opacity increases with total luminosity. Model fits for the most luminous galaxies (brighter than M-5logh=-21.4 in the I band) yield tau₀~=3.5^+4.0_-2.0, near lambda=0.66 mum. The large uncertainty on the inferred value of tau₀ is due to the poorly known characteristics of the distribution of absorbers in the disk, as well as to the likelihood of strong departures from an exponential radial distribution near the galaxy centers. ER - TY - Journal T1 - Faint Galaxy Population in Clusters: X-Ray Emission, cD Halos, and Projection Effects A1 - Valotto, Carlos A. A1 - Muriel, Hernán A1 - Moore, Ben A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 603 Y1 - 2004/3/1 SP - 67 EP - 73 KW - Galaxies: Clusters: General/ Galaxies: Elliptical and Lenticular/ cD/ Galaxies: Luminosity Function/ Mass Function/ X-Rays: Galaxies: Clusters UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...603...67V&db_key=AST&high=42a068d47531540 N2 - We analyze samples of nearby clusters taken from the Abell catalog and the X-Ray Sample of Bright Clusters of De Grandi and coworkers, including a wide range of X-ray luminosities. Using the usually-adopted background subtraction procedures, we find that galaxies in clusters selected by means of their X-ray emission show a flat luminosity function (faint-end slope alpha~=-1.1) consistent with that derived for galaxies in the field and groups. By contrast, the sample of Abell clusters that do not have an X-ray counterpart shows a galaxy luminosity function with a steep faint end (alpha~=-1.6). We investigate the possibility that cD halos could be formed by the disruption of galaxies in rich relaxed clusters that show an apparently flat faint-end galaxy luminosity function. We find that clusters dominated by a central cD galaxy (Bautz-Morgan classes I and II) show the same systematic trend: X-ray-selected clusters have flatter faint-end slopes than those clusters with no detected X-ray emission. Thus, it is likely the X-ray selection and not the cluster domination by central galaxies is what correlates with background decontamination estimates of the galaxy luminosity function. Moreover, no significant correlation between X-ray luminosity and the galaxy luminosity function faint-end slope is found. These results do not support a scenario in which flat faint-end slopes are a consequence of cD formation via the disruption of faint galaxies. We argue that the clusters without X-ray emission are strongly affected by projection effects which give rise to spurious faint-end slopes estimated using background subtraction procedures. ER - TY - Journal T1 - Do Clusters Contain a Large Population of Dwarf Galaxies? A1 - Valotto, Carlos A. A1 - Moore, Ben A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 546 Y1 - 2001/1/1 SP - 157 EP - 164 KW - Galaxies: Clusters: General/ Galaxies: Luminosity Function/ Mass Function/ Methods: Statistical UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...546..157V&db_key=AST&high=42a068d47531540 N2 - We analyze systematic effects in the determination of the galaxy luminosity function in clusters using a deep mock catalog constructed from a numerical simulation of a hierarchical universe. The results indicate a strong tendency to derive a rising faint end (alpha<~-1.5) in clusters selected in two dimensions, using a galaxy catalog constructed with a universal flat luminosity function with alpha~=-1.0. This is a result of the projection effects inherent in catalogs of clusters constructed using two-dimensional data. Many of the clusters found in two dimensions have no significant three-dimensional counterparts, and most suffer from massive background contamination that cannot be corrected for by subtracting random offset fields. The luminosity function of high surface brightness galaxies in the field and within small groups follows a Schechter function with a fairly flat faint-end slope, n(L)~L^alpha, with alpha=-0.9 to -1.2. On the contrary, observational studies of clusters constructed using Abell, EDCC, and APM catalogs are systematically found to have steeper luminosity functions with alpha=-1.4 to -2.0. This may be attributed to projection effects rather than a dominant population of high surface brightness dwarf galaxies (M>~M^*+2) in clusters. It should be straightforward to confirm our results by measuring redshifts of these faint cluster galaxies. ER - TY - Journal T1 - The Dependence of Galaxy Clustering on Luminosity A1 - Valotto, Carlos A. A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 481 Y1 - 1997/5/1 SP - 594 KW - GALAXIES: CLUSTERS: GENERAL/ GALAXIES: STATISTICS/ COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...481..594V&db_key=AST&high=42a068d47531540 N2 - We present statistical results of a two-point galaxy-galaxy cross-correlation function analysis. These studies use appropriate cuts in redshift and limiting apparent magnitude in the two catalogs explored and provide useful information about the dependence of galaxy luminosity on local density. We estimate projected two-point cross-correlation functions w(rp) for samples of center galaxies taken from the Las Campanas Redshift Survey with different mean luminosities against Edinburgh/Durham Southern Catalogue L >~ L* galaxies. Power-law best fits for w(rp) with center galaxies L > L* and L < L* give spatial cross-correlation functions with parameters r0 ~= 5.5 +/- 0.2 h-1 Mpc, gamma ~= 1.8 +/- 0.2 and r0 ~= 3.5 +/- 0.6 h-1 Mpc, gamma ~= 2.2 +/- 0.2, respectively. Possible differences among results of studies of clustering dependence on luminosity reported in previous works might be dominated by systematics because of sample selection effects. Our analyses indicate that the statistical properties of the large-scale distribution of galaxies depend on intrinsic luminosity, arguing against a universal value of the correlation length. Our results suggest a continuous clustering dependence on absolute magnitude, giving support to previous indications that a smaller biasing factor corresponds to low-luminosity galaxies. ER - TY - Journal T1 - The Luminosity Function of Galaxies in Clusters A1 - Valotto, Carlos A. A1 - Nicotra, Mariano A. A1 - Muriel, Hernan A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 479 Y1 - 1997/4/1 SP - 90 KW - GALAXIES: CLUSTERS: GENERAL/ GALAXIES: LUMINOSITY FUNCTION/ MASS FUNCTION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...479...90V&db_key=AST&high=42a068d47531540 N2 - By means of statistical analyses, we compute the luminosity function of galaxies in clusters and explore its dependence on cluster global properties. The data consist of two different samples of southern clusters with published redshifts, taken from the Abell cluster catalog and the APM cluster catalog. Galaxy assignment to the clusters and their corresponding apparent magnitudes were derived from the Edinburgh-Durham Southern Galaxy Catalogue. We have considered two limiting absolute magnitudes, M < -16 and M < -17, comprising 16 and 55 clusters, respectively. The galaxy luminosity function in clusters derived in this work shows a large excess of faint galaxies compared with previous field determinations. In spite of their different identification procedures, we obtain similar galaxy luminosity functions in Abell and APM clusters. A Schechter function with parameters M* ~= -20.0 +/- 0.1 and alpha ~= -1.4 +/- 0.1 provides a satisfactory fit to the galaxy luminosity function of the sample of 55 clusters. We also find a flatter galaxy luminosity function in poor clusters ( alpha ~= -1.2). We have computed errors through a Monte Carlo procedure that considers different possible background corrections and errors in the photometry. Besides providing reliable values of the uncertainties in the luminosity function fitting parameters, this method poses confident limits on the effects of possible systematics. Our results strongly argue against a universal galaxy luminosity function. The high relative frequency of faint galaxies in rich clusters reported in this work may provide constraints on models for the origin and evolution of galaxies. ER - TY - Journal T1 - Distribution of galaxies around clusters: temperature and velocity dispersion dependence A1 - Valotto, Carlos A. A1 - Lambas, Diego G. JO - Monthly Notices of the Royal Astronomical Society VL - 277 Y1 - 1995/12/1 SP - 896 EP - 900 KW - GALAXIES: CLUSTERS: GENERAL/ GALAXIES: FUNDAMENTAL PARAMETERS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995MNRAS.277..896V&db_key=AST&high=42a068d47531540 N2 - We perform a cross-correlation analysis of galaxy counts on Lick maps and rich clusters of galaxies with measured temperatures T and velocity dispersions sigma. We find that galaxy density excesses up to ~20 Mpc from cluster centres are increasing linear functions on sigma and T with a statistically significant detection (<~99.99 per cent confidence determined by the method of resampling). Adopting a power-law model for the cluster-galaxy cross-correlation function we find that the cross-correlation length r_0 obeys the simple relations: r_0=8.8 (sigma/970)^1/2.2 Mpc and r_0=8.8 (T/4.8)^1/2.2 Mpc, where sigma is in km s^-1 and T in keV. ER - TY - Journal T1 - Lyngå 1, A Small Open Cluster Containing a Red-Supergiant Member A1 - Vázquez, R. A. A1 - Giorgi, E. E. A1 - Brusasco, M. A. A1 - Baume, G. A1 - Solivella, G. R. JO - Revista Mexicana de Astronomia y Astrofisica VL - 39 Y1 - 2003/4/1 SP - 89 EP - 105 KW - open clusters and associations: individual (Lyngå 1)/ stars: mass function/ spectral classification/ stars: polarization UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003RMxAA..39...89V&db_key=AST&high=42a068d47502302 N2 - We present CCD {UBV}RI} (Cousins system) photometric observations complemented with spectroscopic and polarimetric observations that were carried out in the open cluster Lyngå 1. Our data indicate that the cluster reddening is E(B-V)= 0.45+/-0.03, the ratio A[V]/E(B-V)= R suggests that the extinction law may be slightly anomalous ( R â‰ˆ 3.5) and that the cluster distance modulus is V₀ - M[V] = 11.40+/-0.2. The age of Lyngå 1 is between 100 and 125 Myr according to a fitting of theoretical isochrones, and the slope of its mass spectrum is x â‰ˆ 1.7. The brightest red star in the field is a cluster member of spectral type K2 II-Ib. ER - TY - Journal T1 - Multiwavelength Observations of the Peculiar Planetary Nebula IC 2149 A1 - Vázquez, R. A1 - Miranda, L. F. A1 - Torrelles, J. M. A1 - Olguín, L. A1 - Benítez, G. A1 - Rodríguez, L. F. A1 - López, J. A. JO - Astrophysical Journal VL - 576 Y1 - 2002/9/1 SP - 860 EP - 869 KW - ISM: Kinematics and Dynamics/ ISM: Planetary Nebulae: Individual: Alphanumeric: IC 2149/ Stars: AGB and Post-AGB UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...576..860V&db_key=AST&high=42a068d47502302 N2 - We report high- and low-dispersion spectroscopy, optical imaging, and high-resolution Very Large Array-A lambda3.6 cm continuum observations of the peculiar planetary nebula IC 2149. These observations show that ``bipolar'' is a suitable morphological classification for IC 2149. Most nebular material is concentrated in a knotty, bright ring seen edge-on, embedded in an apparently oblate ellipsoidal shell from which remnant or incipient bipolar lobes emerge. We confirm the previously reported depletion in heavy elements and deduce a very low ejected nebular mass <~0.03 M_solar. All this information indicates that the formation of IC 2149 is the result of the evolution of a low-mass central star. ER - TY - Journal T1 - The open cluster Havlen-Moffat No. 1 revisited A1 - Vázquez, R. A. A1 - Baume, G. JO - Astronomy and Astrophysics VL - 371 Y1 - 2001/6/1 SP - 908 EP - 920 KW - CLUSTER: OPEN/ INDIVIDUAL: HAVLEN-MOFFAT NO. 1/ STARS: IMAGING/ STARS: LUMINOSITY FUNCTION/ MASS FUNCTION/ ISM: DUST/ EXTINCTION UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...371..908V&db_key=AST&high=42a068d47502302 N2 - A deep CCD UBVRI photometric survey combined with UBVRI polarimetric observations of 21 bright stars was carried out in the region of the open cluster Havlen-Moffat No. 1. Our data reveal that the extinction law in this cluster is variable and that six cluster stars show very high polarisation values (>4%), probably because of the presence of a nearby small dust cloud. The cluster is at a distance of d = 3300 pc, it is 2-4 Myr old and the initial mass function of its most massive stars (M > 3 M_sun) has a flat slope of x~ 0.7. As an additional result, it was possible to reconcile the absolute magnitudes of the two WN7-type members using the R-values valid in the regions where they are located. Based on observations collected at the University of Toronto Southern Observatory, Las Campanas, Chile, and the Complejo Astronómico El Leoncito, (CASLEO), Argentina, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan. Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/371/908. ER - TY - Journal T1 - UBVRI imaging photometry of the open cluster CR 272 A1 - Vazquez, R. A. A1 - Baume, G. A1 - Feinstein, A. A1 - Prado, P. JO - Astronomy and Astrophysics Supplement Series VL - 124 Y1 - 1997/7/1 SP - 13 EP - 21 KW - CLUSTER: OPEN: INDIVIDUAL: CR 272/ STARS: LUMINOSITY FUNCTION/ MASS FUNCTION/ HR DIAGRAM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26AS..124...13V&db_key=AST&high=42a068d47502302 N2 - We present an extensive CCD UBVRI (Cousins system) photometric survey in the region of the open cluster Collinder 272. Our data analysis confirms that the cluster is situated in the outer border of Becker's inner arm -II, at a distance d=2300 pc and probably related to the neighbor cluster Hogg 16. There is no highly evolved stars in the cluster upper sequence and our age estimate based upon isochrones from models computed with mass loss and overshooting, and other methods, indicates a mean age of 13 Myr. A statistical method based on the removal of field stars was used to determine the luminosity function and the initial mass function of the cluster. The cluster initial mass function is characterized by a slope x=1.8. Based on observations collected at the University of Toronto Southern Observatory, Las Campanas, Chile. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html ER - TY - Journal T1 - An analytical approach to fluctuations in showers A1 - Vázquez, R. A. JO - Astroparticle Physics VL - 6 Y1 - 1997/3/1 SP - 411 EP - 422 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997APh.....6..411V&db_key=AST&high=42a068d47502302 N2 - We review the problem of fluctuations in particle shower theory. By using a generalization of Furry equation, we find relations between the n-particle correlation function and the number of particles average or 1-particle correlation function. Such relations show that the average is the only independent dynamical variable. We also develop a numerical code to solve the equation for the correlation functions and compare the results with those from a Monte Carlo simulation which show a perfect agreement between both methods. ER - TY - Journal T1 - Investigation on the region of the open cluster TR 14. A1 - Vazquez, R. A. A1 - Baume, G. A1 - Feinstein, A. A1 - Prado, P. JO - Astronomy and Astrophysics Supplement Series VL - 116 Y1 - 1996/3/1 SP - 75 EP - 94 KW - OPEN CLUSTER: TR 14/ STARS: HD 93129AB/ HD 93161EW/ STARS: MASS FUNCTION/ STARS: PRE-MAIN SEQUENCE/ HR DIAGRAM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26AS..116...75V&db_key=AST&high=42a068d47502302 N2 - We present UBVRI CCD imaging photometry down to approximately V=19mag in the area of the very young open cluster Tr 14. Our results confirm the existence of an anomalous extinction law in the area if it is interpreted in terms of the UBVRI photometry. According to our analysis the cluster distance is d=3100 (V_0_-M_V_=12.50mag) and its age is 1.5+/-.5x10^6^y. We want to draw the attention on stars which, from the observed magnitude-spread at constant color, could be stars in an early stage of evolution. In that case, the observed spread leads to assume that the process of star formation in Tr 14 is continuous whereas, from pre-main sequence evolutionary tracks, a duration of about 5x10^6^y is deduced for it. The computation of the cluster initial mass function reveals a flat slope even though it still compares to a Salpeter law. At the same time, we found a spatial variation of the cluster IMF, which could be explained by mass segregation in the star formation process. The cluster youth and its compact appearance seem to confirm that it is far from virial equilibrium. The observed total cluster mass is around 2000M_sun_ and its core contains about 40% of the total. ER - TY - Journal T1 - A detailed study of the open cluster PISMIS 20. A1 - Vazquez, R. A. A1 - Will, J.-M. A1 - Prado, P. A1 - Feinstein, A. JO - Astronomy and Astrophysics Supplement Series VL - 111 Y1 - 1995/5/1 SP - 85 KW - OPEN CLUSTER: PIS 20/ STARS: MASS FUNCTION/ STARS: WR/ INDIVIDUAL: WR 67/ WOLF-RAYET UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26AS..111...85V&db_key=AST&high=42a068d47502302 N2 - The very young open cluster Pis 20 has been investigated using CCD UBVR photometry. New blue faint members were found down to V=19mag. With them we obtain a better definition of the lower cluster main sequence. Using the fitting method, we derive a cluster distance of d=3600pc (V_0_-M_V_=12.80). The mean color excess is =1.24mag. From the observed characteristics and spatial location of the bluest cluster stars we conclude that the star WR 67 has a good chance to be a cluster member. In that case, the mass of its progenitor should be greater than 50M_sun_ according to evolutionary models. We obtain for Pis 20 an age of 5(+/-1)x10^6^yr from isochrone fitting. We discuss the cluster's mass spectrum whose slope, within the observational uncertainties, appears to be similar to the one in Salpeter's law. We notice that high WR/OB and WC/WN number ratios are present not only within the cluster itself but also in the association where Pis 20 is situated. Although the cluster distance derived here places Pis 20 nearer than the supernova remnant MSH 15-52, we cannot/rule out the possibility that they are spatially related. The presently observed cluster mass is around 600M_sun_. ER - TY - Journal T1 - Time-dependent ejection velocity model for the outflow of Hen 3-1475 A1 - Velázquez, P. F. A1 - Riera, A. A1 - Raga, A. C. JO - Astronomy and Astrophysics VL - 419 Y1 - 2004/6/1 SP - 991 EP - 998 KW - ISM: jets and outflows/ planetary nebulae: individual: Hen 3-1475/ methods: numerical/ hydrodynamics UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...419..991V&db_key=AST&high=42a068d47507965 N2 - We present 2D axisymmetric and 3D numerical simulations of the proto-planetary nebula Hen 3-1475, which is characterized by a remarkably highly collimated optical jet, formed by a string of shock-excited knots along the axis of the nebula. It has recently been suggested that the kinematical and morphological properties of the Hen 3-1475 jet could be the result of an ejection variability of the central source (Riera et al. \cite{Riera03}). The observations suggest a periodic variability of the ejection velocity superimposed on a smoothly increasing ejection velocity ramp. From our numerical simulations, we have obtained intensity maps (for different optical emission lines) and position-velocity diagrams, in order to make a direct comparison with the HST observations of this object. Our numerical study allows us to conclude that a model of a precessing jet with a time-dependent ejection velocity, which is propagating into an ISM previously perturbed by an AGB wind, can succesfully explain both the morphological and the kinematical characteristics of this proto-planetary nebula. Based on observations made with the Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. ER - TY - Journal T1 - Effects of Thermal Conduction on the X-Ray and Synchrotron Emission from Supernova Remnants A1 - Velázquez, Pablo F. A1 - Martinell, Julio J. A1 - Raga, Alejandro C. A1 - Giacani, Elsa B. JO - Astrophysical Journal VL - 601 Y1 - 2004/2/1 SP - 885 EP - 895 KW - Conduction/ ISM: Magnetic Fields/ Methods: Numerical/ ISM: Supernova Remnants/ X-Rays: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...601..885V&db_key=AST&high=42a068d47507965 N2 - Several physical mechanisms have been studied in order to explain why composite supernova remnants (SNRs) have shell-like morphologies in the radio continuum while their X-ray emission is centrally peaked. One of the proposed mechanisms has been the presence of thermal conduction, which can raise the density at the center of SNRs, increasing the X-ray emission from these regions. In this work, we have carried out axisymmetric numerical simulations with the adaptive grid Yguazú-a code, which includes advection of the magnetic field and thermal conduction. We have considered cases with anisotropic and isotropic thermal conduction, as well as with no conduction. We have simulated X-ray (as well as radio synchrotron) emission maps from our numerical simulations, which can be directly compared with observations. ER - TY - Journal T1 - A Supernova Remnant Collision with a Stellar Wind A1 - Velázquez, Pablo F. A1 - Koenigsberger, Gloria A1 - Raga, Alejandro C. JO - Astrophysical Journal VL - 584 Y1 - 2003/2/1 SP - 284 EP - 292 KW - Galaxies: Magellanic Clouds/ Stars: Individual: Henry Draper Number: HD 5980/ Stars: Winds/ Outflows/ ISM: Supernova Remnants/ X-Rays: ISM UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...584..284V&db_key=AST&high=42a068d47507965 N2 - Numerical simulations of the interaction between supernova ejecta and a stellar wind are presented. We follow the temporal evolution of the shock fronts that are formed through such an interaction and determine the velocities, temperatures, and densities. We model the X-ray emission from the supernova remnant-stellar wind collision region, and we compare it with recent results from X-ray observations carried out with the Chandra satellite of the SMC supernova remnant SNR 0057-7226, which could be interacting with the wind of the Wolf-Rayet system HD 5980. The simulations predict the presence of shell-like regions of enhanced X-ray emission that are consistent with the presence of X-ray-emitting arcs in the Chandra image. Also, the observed X-ray luminosity is comparable to the X-ray luminosities we obtain from the simulations for a supernova with an initial energy in the (1-5)×10⁵⁰ ergs range. ER - TY - Journal T1 - Investigation of the Large-scale Neutral Hydrogen near the Supernova Remnant W28 A1 - Velázquez, P. F. A1 - Dubner, G. M. A1 - Goss, W. M. A1 - Green, A. J. JO - Astronomical Journal VL - 124 Y1 - 2002/10/1 SP - 2145 EP - 2151 KW - ISM: H I/ ISM: Individual: Alphanumeric: W28/ ISM: Structure/ ISM: Supernova Remnants UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....124.2145V&db_key=AST&high=42a068d47507965 N2 - The distribution and kinematics of neutral hydrogen have been studied in a wide area around the supernova remnant (SNR) W28. A 2.5d×2.5d field centered at l=6.5d, b=0° was surveyed using the Parkes 64 m radio telescope (half-power beamwidth of 14.7' at lambda21 cm). Even though W28 is located in a complex zone of the Galactic plane, we have found different H I features, which are evidence of the interaction between W28 and its surrounding gas. An extended cold cloud with about 70 M_solar of neutral hydrogen was detected at the location of W28 as a self-absorption feature, near the local standard of rest velocity of +7 km s^-1. This H I feature is the atomic counterpart of the molecular cloud shown by previous studies to be associated with W28. From this detection, we can independently confirm a kinematical distance of about 1.9 kpc for W28. In addition, the neutral hydrogen observed in emission around the SNR displays a ringlike morphology in several channel maps over the velocity interval [-25.0, +38.0] km s^-1. We propose that these features are part of an interstellar H I shell that has been swept up by the supernova shock front. Emission from this shell is confused with unrelated gas. Hence, we derive an upper limit for the shell mass of 1200-1600 M_solar, a maximum radius of the order of 20 pc, an expansion velocity of ~30 km s^-1, an initial energy of about 1.4-1.8×10⁵⁰ ergs, and an age of ~3.3×10⁴ yr. The preexisting ambient medium has a volume density on the order of 1.5-2 cm^-3. W28 is probably in the radiative evolutionary phase, although it is not possible to identify the recombined thin neutral shell expected to form behind the shock front with the angular resolution of the present survey. ER - TY - Journal T1 - A single explosion model for the supernova remnant 3C 400.2 A1 - Velázquez, P. F. A1 - de la Fuente, E. A1 - Rosado, M. A1 - Raga, A. C. JO - Astronomy and Astrophysics VL - 377 Y1 - 2001/10/1 SP - 1136 EP - 1144 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...377.1136V&db_key=AST&high=42a068d47507965 N2 - We present a numerical simulation carried out in order to explain the complex morphology of the supernova remnant (SNR) 3C 400.2. Numerical simulations were done employing the new yguazú-a code (Raga et al. 2000). In the radio continuum, this remnant seems to be formed by two shells, which are partially overlapping (\cite{dubner94}). Taking into account observational evide nce such as a previous HI study (\cite{giacani98}), we find that an adequate model for describing the morphology of the SNR 3C 400.2 is obtained by assuming that a single supernova (SN) explosion took place in a dense medium and close to an interface separating this medium from a lower density region. Besides, we also present a new deeper CCD Halpha image mosaic of the north-west region of this SNR, which is composed of three single images. From the numerical results, we generated Halpha emission maps, obtaining a good agreement with the observations. ER - TY - Journal T1 - Laboratory Experiments and Numerical Models of Interacting Explosions A1 - Velázquez, P. F. A1 - Sobral, H. A1 - Raga, A. C. A1 - Villagrán-Muniz, M. A1 - Navarro-González, R. JO - Revista Mexicana de Astronomia y Astrofisica VL - 37 Y1 - 2001/4/1 SP - 87 EP - 94 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001RMxAA..37...87V&db_key=AST&high=42a068d47507965 N2 - We present laboratory experiments and numerical simulations of the interaction between two explosions. In the laboratory, two expanding shock waves were produced using two Nd: YAG lasers, and the numerical simulations were carried out with the yguazú-a code (Raga et al. 2000). We show that the numerical simulations and laboratory experiments agree in a satisfactory way, and we discuss the general properties of the resulting flows. Finally, we discuss the similarities and differences between the laboratory experiments and some astrophysical objects. ER - TY - Journal T1 - A numerical simulation of the W 50-SS 433 system A1 - Velázquez, P. F. A1 - Raga, A. C. JO - Astronomy and Astrophysics VL - 362 Y1 - 2000/10/1 SP - 780 EP - 785 KW - ISM: SUPERNOVA REMNANTS/ STARS: SUPERNOVAE: INDIVIDUAL: W 50/ ISM: JETS AND OUTFLOWS/ HYDRODYNAMICS/ METHODS: NUMERICAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...362..780V&db_key=AST&high=42a068d47507965 N2 - We present results of numerical simulations performed to study the evolution and interaction of jets propagating inside of Supernova Remnants (SNRs). There are new observations which show this kind of jet/SNR interaction (\cite{dubner98}, \cite{gaensler98}). From our numerical simulations, we compute synchrotron emission maps, in order to directly compare the numerical results with the radio maps. Our aim is to explain the strange morphologies some SNRs exhibit in the radio-continuum, such as the case of SNR W 50 in which a shell is interacting with the jets from the SS 433 source. In recent radio images (at 328 and 1465 MHz, \cite{dubner98}), the SNR W 50 shows a helical structure in its Eastern lobe. Our numerical results are consistent with the radio-continuum observations, and reveal that a probable origin for the helical structure in the Eastern lobe of W 50, is the generation of incident and reflected secondary shock waves in the jet beam. Furthermore the simulations show that the cocoon gas is pushing out the SNR shell, filling up its interior, and increasing the expansion velocity of the shell. ER - TY - Journal T1 - Study of the Rayleigh-Taylor instability in Tycho's supernova remnant A1 - Velazquez, P. F. A1 - Gomez, D. O. A1 - Dubner, G. M. A1 - de Castro, G. Gimenez A1 - Costa, A. JO - Astronomy and Astrophysics VL - 334 Y1 - 1998/6/1 SP - 1060 EP - 1067 KW - ISM: SUPERNOVA REMNANTS/ SHOCK WAVES/ ISM: INDIVIDUAL: TYCHO SNR/ HYDRODYNAMICS/ INSTABILITIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26A...334.1060V&db_key=AST&high=42a068d47507965 N2 - In the present paper we investigate the linear stage of instabilities which might take place at the shock front of young supernova remnants (hereafter SNR), deriving expressions for the characteristic wavelength and typical growth time scales. These theoretical predictions are compared with very high resolution observations of Tycho's SNR obtained with the Very Large Array at 1.4 GHz. The images obtained with an angular resolution of the order of 1 arcsec and with very good sensitivity, clearly reveal the presence of corrugated (wavelike) structures with remarkable spatial regularity, visible mainly along the northeastern part of the SNR shell. We argue that the Rayleigh-Taylor instability (hereafter R-T ) is responsible for the observed structures. Using physical parameters of Tycho's remnant and its environment derived from different X-ray observational studies, we computed the expected wavelength and growth rate for the most unstable R-T mode including viscosity and magnetic effects. The wavelength we derive is fully compatible with the one measured directly on the image (lambda_ {obs} ~ 0.9 \ pc). The growth rate derived for this mode indicates that the R-T instability is still undergoing its linear stage. ER - TY - Journal T1 - Constraints on the Wind Structure of OB Stars from Theoretical He II Lines A1 - Venero, Roberto O. J. A1 - Cidale, Lydia S. A1 - Ringuelet, Adela E. JO - Astrophysical Journal VL - 578 Y1 - 2002/10/1 SP - 450 EP - 463 KW - Line: Formation/ Radiative Transfer/ Stars: Atmospheres/ Stars: Early-Type UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...578..450V&db_key=AST&high=42a068d47509065 N2 - Theoretical profiles of He II lines in OB stars with an expanding, spherically symmetric atmosphere are computed. The extended atmospheric model is formed by a classical photosphere, characterized by the effective temperature and the surface gravity, and superimposed layers that have different velocity and temperature structure. We solve rigorously the radiative transfer equation, simultaneously with the statistical equilibrium equations for multilevel atoms, by making use of Feautrier's method in the comoving frame. We discuss the influence on the He II lines of the hydrodynamic and thermodynamic structure of the atmosphere, paying special attention to those configurations that give rise to emission lines. The main conclusions of our work can be summarized as follows:1. The shape of the profiles is determined by the velocity gradient at the base of the wind whenever a positive temperature gradient occurs.2. In O-type stars, the emission-line intensity depends quite sensitively on logg, in agreement with the Walborn luminosity criterion.3. In addition, we are able to produce emission and absorption profiles that are in qualitative agreement with those observed in O and B stars.4. We also confirm the previous Cidale & Ringuelet and Venero, Cidale, & Ringuelet results that showed that a warm, extended, and rapidly expanding atmosphere is sufficient to give rise to emission components in the line profiles. ER - TY - Journal T1 - Collisions of non-rotating spherical galaxies A1 - Vergne, M. Marcela A1 - Muzzio, Juan C. JO - Monthly Notices of the Royal Astronomical Society VL - 276 Y1 - 1995/9/1 SP - 439 EP - 452 KW - METHODS: NUMERICAL/ GALAXIES: EVOLUTION/ GALAXIES: INTERACTIONS/ GALAXIES: STRUCTURE UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995MNRAS.276..439V&db_key=AST&high=42a068d47509678 N2 - We have used self-consistent numerical simulations of N-body systems to investigate encounters between spherical non-rotating galaxies. In our simulations, the galaxies were represented by Plummer spheres (rho~r^-5) with isotropic velocity distribution, and we considered collisions along hyperbolic, as well as a few parabolic, orbits. Pairs of galaxies with several different mass ratios (1:1, 1:2, 1:4 and 1:8) were included. We analysed the effects on the internal structure of the galaxies caused by collisions that did not result in mergers after one Hubble time, quantitatively estimating the changes in linear size, mass and energy, and discussing their possible correlations with the orbital parameters. Besides this, we used the results of collisions that ended up in mergers to investigate the structure of the remnants (with respect to binding energy, mass loss, linear size and flattening). We also obtained the density profiles of the remnants, which are well described by an r^-gamma law profile with 3solar white dwarf model in a self-consistent way with the evolution of chemical abundance distribution as given by time-dependent diffusion processes. Results are compared with the standard treatment of diffusive equilibrium in the trace element approximation. Appreciable differences are found between the two employed treatments. We conclude that time-dependent element diffusion plays an important role in determining the whole oscillation pattern and the temporal derivative of the periods in DAV white dwarfs. In addition, we discuss the plausibility of the standard description employed in accounting for diffusion in most white dwarf asteroseismological studies. ER - TY - Journal T1 - The mode trapping properties of full DA white dwarf evolutionary models A1 - Córsico, A. H. A1 - Althaus, L. G. A1 - Benvenuto, O. G. A1 - Serenelli, A. M. JO - Astronomy and Astrophysics VL - 387 Y1 - 2002/5/1 SP - 531 EP - 549 KW - stars: evolution/ stars: interiors/ stars: white dwarfs/ stars: oscillations UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...387..531C&db_key=AST&high=42a068d47504913 N2 - An adiabatic, non-radial pulsation study of a 0.563 M_sun DA white dwarf model is presented on the basis of new evolutionary calculations performed in a self-consistent way with the predictions of time dependent element diffusion, nuclear burning and the history of the white dwarf progenitor. Emphasis is placed on the role played by the internal chemical stratification of these new models in the behaviour of the eigenmodes, and the expectations for the full g-spectrum of periods. The implications for the mode trapping properties are discussed at length. In this regard, we find that, for high periods, the viability of mode trapping as a mode selection mechanism is markedly weaker for our models, as compared with the situation in which the hydrogen-helium transition region is treated assuming equilibrium diffusion in the trace element approximation. ER - TY - Journal T1 - A New Code for Nonradial Stellar Pulsations and its Application to Low-Mass, Helium White Dwarfs A1 - Córsico, A. H. A1 - Benvenuto, O. G. JO - Astrophysics and Space Science VL - 279 Y1 - 2002/1/1 SP - 281 EP - 300 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Ap%26SS.279..281C&db_key=AST&high=42a068d47504913 N2 - We present a finite difference code intended for computing linear, adiabatic, nonradial pulsations of spherical stars. This code is based on a slight modification of the general Newton-Raphson technique in order to handle the relaxation of the eigenvalue (square of the eigenfrequency) of the modes and their corresponding eigenfunctions. This code has been tested computing the pulsation spectra of polytropic spheres finding a good agreement with previous work. Then, we have coupled this code to our evolutionary code and applied it to the computation of the pulsation spectrum of a low mass, pure-helium white dwarf of 0.3 M_solar for a wide range of effective temperatures. In making this calculation we have taken an evolutionary time step short enough such that eigenmodes corresponding to a given model are used as initial approximation to those of the next one. Specifically, we have computed periods, period spacing, eigenfunctions, weight functions, kinetic energies and variational periods for a wide range of modes. To our notice this is the first effort in studying the pulsation properties of helium white dwarfs. The solution we have found working with these realistic white dwarf models are in good accord with the predictions of the asymptotic theory of Tassoul (1980) for high order modes. This indicates that the code presented here is able to work adequately also with realistic stellar models. ER - TY - Journal T1 - New DA white dwarf evolutionary models and their pulsational properties A1 - Córsico, A. H. A1 - Althaus, L. G. A1 - Benvenuto, O. G. A1 - Serenelli, A. M. JO - Astronomy and Astrophysics VL - 380 Y1 - 2001/12/1 SP - L17 EP - L20 KW - STARS: EVOLUTION/ STARS: INTERIORS/ STARS: WHITE DWARFS/ STARS: OSCILLATIONS UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...380L..17C&db_key=AST&high=42a068d47504913 N2 - In this letter we investigate the pulsational properties of ZZ Ceti stars on the basis of new white dwarf evolutionary models calculated in a self-consistent way with the predictions of time dependent element diffusion and nuclear burning. In addition, full account is taken of the evolutionary stages prior to the white dwarf formation. Emphasis is placed on the trapping properties of such models. By means of adiabatic, non-radial pulsation calculations, we find, as a result of time dependent diffusion, a much weaker mode trapping effect, particularly for the high-period regime of the pulsation g-spectrum. This result is valid at least for models with massive hydrogen-rich envelopes. Thus, mode trapping would not be an effective mechanism to explain the fact that all the high periods expected from standard models of stratified white dwarfs are not observed in the ZZ Ceti stars. ER - TY - Journal T1 - The potential of the variable DA white dwarf G117-B15A as a tool for fundamental physics A1 - Córsico, A. H. A1 - Benvenuto, O. G. A1 - Althaus, L. G. A1 - Isern, J. A1 - García-Berro, E. JO - New Astronomy VL - 6 Y1 - 2001/6/1 SP - 197 EP - 213 UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001NewA....6..197C&db_key=AST&high=42a068d47504913 N2 - White dwarfs are well studied objects. The relative simplicity of their physics allows one to obtain very detailed models which can be ultimately compared with their observed properties. Among white dwarfs there are specific classes of stars, known as ZZ-Ceti objects, which have a hydrogen-rich envelope and show periodic variations in their light curves. G117-B15A belongs to this particular set of stars. The luminosity variations have been successfully explained as due to /g-mode pulsations. G117-B15A has recently claimed to be the most stable optical clock ever found, being the rate of change of its 215.2 s period very small: PÌ‡=(2.3+/-1.4)×10^-15 ss^-1, with a stability comparable to that of the most stable millisecond pulsars. The rate of change of the period is closely related to its cooling timescale, which can be accurately computed. In this paper we study the pulsational properties of G117-B15A and we use the observed rate of change of the period to impose constraints on the axion emissivity and thus, to obtain a preliminary upper bound to the mass of the axion. This upper bound turns out to be 4 cos²betameV at the 95% confidence level. Although there are still several observational and theoretical uncertainties, we conclude that G117-B15A is a very promising stellar object to set up constraints on particle physics. ER - TY - Journal T1 - Crustal thinning in the Southwestern Iberia Margin A1 - González, A. A1 - Torné, M. A1 - Córdoba, D. A1 - Vidal, N. A1 - Matias, L. M. A1 - Díaz, J. JO - Geophysical Research Letters VL - 23 Y1 - 1996/1/1 SP - 2477 EP - 2480 KW - Marine Geology and Geophysics: Marine seismics/ Exploration Geophysics: Seismic methods/ Marine Geology and Geophysics: Gravity/ Exploration Geophysics: Data processing UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996GeoRL..23.2477G&db_key=AST&high=42a068d47524183 N2 - The mode of crustal thinning in the southwestern margin of the Iberian Peninsula is investigated along a transect that extends from onshore Iberia to the eastern end of the Horseshoe Abyssal Plain. On onshore areas, the crustal structure has been deduced using wide-angle seismic reflection data, whereas offshore we have used coincident steep and wide-angle reflection data along a NE-SW oriented seismic profile that extends from Cape San Vicente to the Horseshoe Abyssal Plain. In addition, 2D gravity modelling has been performed to validate the crustal structure deduced from seismic data. Our model results reveal that the crust undergoes a strong but continuous thinning from 31 km onshore Iberia to less than 15 km in the Horseshoe Abyssal Plain and that thinning occurs over horizontal distances of about 120 km. ER - TY - Journal T1 - Spectroscopic Binaries and Kinematic Membership in the Open Cluster NGC 3532 A1 - González, Jorge Federico A1 - Lapasset, Emilio JO - Astronomical Journal VL - 123 Y1 - 2002/6/1 SP - 3318 EP - 3324 KW - Stars: Binaries: Spectroscopic/ Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 3532/ Techniques: Radial Velocities UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123.3318G&db_key=AST&high=42a068d47527134 N2 - We report spectroscopic observations for bright stars in the open cluster NGC 3532 up to 1 mag below the turnoff point. We compute radial velocities by cross-correlations and determine spectral types and rotational velocities. Using 21 stars identified as certain members, we derive a mean cluster velocity of +3.4+/-0.3 km s^-1. From radial velocities and angular distances to the cluster center, we compute membership probabilities for all but two stars that are radial velocity variables. Only one out of 34 program stars is a clear kinematic nonmember. Three spectroscopic binaries and three additional possible radial velocity variables are detected among the 23 stars measured more than once. We report the star HD 96609 as a double-lined spectroscopic binary. Using the two-dimensional cross-correlation technique TODCOR developed by Zucker & Mazeh, we derive the radial velocity curves for both components and obtain the orbital parameters with errors of 0.3% and 0.7% for the projected orbital semiaxis and masses, respectively. This system is composed of two main-sequence stars in a circular orbit, with a period of 8.19 days. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the National Universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - Radial Velocities and Kinematic Membership in the Open Cluster NGC 3114 A1 - González, Jorge Federico A1 - Lapasset, Emilio JO - Astronomical Journal VL - 121 Y1 - 2001/5/1 SP - 2657 EP - 2663 KW - Stars: Blue Stragglers/ Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 3114/ Techniques: Radial Velocities UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121.2657G&db_key=AST&high=42a068d47527134 N2 - Echelle spectroscopic observations for 30 bright stars in the field of the sparse open cluster NGC 3114 are presented. The sample includes main-sequence stars, yellow and red giants, and blue straggler candidates. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. The cluster mean velocity is well defined from eight giants and several main-sequence stars whose average is =-3.52+/-0.25 km s^-1. The membership probabilities of the observed stars are computed on the basis of the velocity distributions of the cluster and field stars, and the expected percentage of contamination at each position. We classified 19 cluster members and 10 nonmembers; the remaining star is a known spectroscopic binary for which no membership probability was assigned. Among the members, there is a bright yellow giant, seven red giants, and four blue straggler candidates, although they should be considered as turn-off stars. The location of two of them in the color-magnitude diagram (slightly blueward of the turn-off) can be explained by their low rotational velocities. No velocity variations were detected in the 16 stars measured more than once, which indicates that NGC 3114 possess an abnormally low binary frequency. From spectral types of cluster members, a distance modulus (V-M_v)=9.8+/-0.2 mag and a reddening E(B-V)=0.07+/-0.01 mag are derived. The cluster age is estimated to be 1.6×10⁸ yr. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the National Universities of La Plata, Córdoba and San Juan. ER - TY - Journal T1 - Radial Velocities, Binarity, and Kinematic Membership in the Open Cluster NGC 2516 A1 - González, Jorge Federico A1 - Lapasset, Emilio JO - Astronomical Journal VL - 119 Y1 - 2000/5/1 SP - 2296 EP - 2302 KW - STARS: BINARIES: SPECTROSCOPIC/ STARS: BLUE STRAGGLERS/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC NUMBER: NGC 2516/ TECHNIQUES: RADIAL VELOCITIES UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....119.2296G&db_key=AST&high=42a068d47527134 N2 - We present echelle spectroscopic observations for 36 bright (V<9.6) stars in the open cluster NGC 2516, including several blue straggler candidates and four red giants. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. From 22 cluster members a mean cluster velocity of +22.0+/-0.2 km s^-1 was derived. Membership probabilities of the observed stars are computed on the basis of their distance to the cluster center and kinematic criteria. We report the discovery of three double-lined spectroscopic binaries and several probable binaries among main-sequence stars. A binary frequency of more than 26% is found among the high-mass main-sequence stars. The blue straggler HD 66341 is a slowly rotating cluster member with constant velocity, while HD 66194 is a fast-rotating Be star with probable variations in radial velocity. Other blue straggler candidates, such as HD 65663, 65950, 66066, and 65987, must be considered turnoff stars. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the national universities of La Plata, Córdoba, and San Juan. ER - TY - Journal T1 - Magnetic twist and writhe of active regions. On the origin of deformed flux tubes A1 - López Fuentes, M. C. A1 - Démoulin, P. A1 - Mandrini, C. H. A1 - Pevtsov, A. A. A1 - van Driel-Gesztelyi, L. JO - Astronomy and Astrophysics VL - 397 Y1 - 2003/1/1 SP - 305 EP - 318 KW - magnetic fields/ methods: data analysis/ Sun: interior/ Sun: magnetic fields/ Sun: photosphere UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...397..305L&db_key=AST&high=42a068d47519327 N2 - We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows. ER - TY - Journal T1 - The Counterkink Rotation of a Non-Hale Active Region A1 - López Fuentes, M. C. A1 - Demoulin, P. A1 - Mandrini, C. H. A1 - van Driel-Gesztelyi, L. JO - Astrophysical Journal VL - 544 Y1 - 2000/11/1 SP - 540 EP - 549 KW - Sun: Activity/ Sun: Corona/ Sun: Interior/ Sun: Magnetic Fields UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...544..540L&db_key=AST&high=42a068d47519327 N2 - We describe the long-term evolution of a bipolar non-Hale active region that was observed from 1995 October to 1996 January. During these four solar rotations the sunspots and subsequent flux concentrations, during the decay phase of the region, were observed to move in such a way that by December their orientation conformed to the Hale-Nicholson polarity law. The sigmoidal shape of the observed soft X-ray coronal loops allows us to determine the sense of the twist in the magnetic configuration. This sense is confirmed by extrapolating the observed photospheric magnetic field, using a linear force-free approach, and comparing the shape of computed field lines with the observed coronal loops. This sense of twist agrees with that of the dominant helicity in the solar hemisphere where the region lies, as well as with the evolution observed in the longitudinal magnetogram during the first rotation. At first sight the relative motions of the spots may be misinterpreted as the rising of an Omega loop deformed by a kink instability, but we deduce from the sense of their relative displacements a handedness for the flux-tube axis (writhe) that is opposite to that of the twist in the coronal loops and, therefore, to what is expected for a kink-unstable flux tube. After excluding the kink instability, we interpret our observations in terms of a magnetic flux tube deformed by external motions while rising through the convective zone. We compare our results with those of other related studies, and we discuss, in particular, whether the kink instability is relevant to explain the peculiar evolution of some active regions. ER - TY - Journal T1 - Astrometry with Virtual Observatories A1 - López, Carlos E. JO - Astrophysics and Space Science VL - 290 Y1 - 2004/4/1 SP - 439 EP - 447 KW - astrometry/ databases/ new techniques UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..439L&db_key=AST&high=42a068d47521753 N2 - With the advent of virtual observatories, most astrometry-oriented projects being currently developed---and those to come in the near future---will be greatly enriched. Among these projects it is worth mentioning double stars and multiple systems, proper-motion detections, identification of lost high-proper-motion stars, a detailed census of open cluster members, and precovery of natural satellites, minor planets and comets. A brief discussion of some of these studies is presented. To accomplish the goals proposed by the virtual observatories concept, a massive amount of high-quality astrometric data is needed in advance. It is shown that today's astrometry is about to ready to face these new challenges. ER - TY - Journal T1 - Determination of the linear mass power spectrum from the mass function of galaxy clusters A1 - Sánchez, Ariel G. A1 - Padilla, Nelson D. A1 - Lambas, Diego G. JO - Monthly Notices of the Royal Astronomical Society VL - 337 Y1 - 2002/11/1 SP - 161 EP - 171 KW - cosmology: theory/ large-scale structure of Universe UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.337..161S&db_key=AST&high=42a068d47513999 N2 - We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation sigma(M) using the expression for the mass function in the Press & Schechter, Sheth, Mo & Tormen and Jenkins et al. formalisms. We apply different techniques to recover the adimensional power spectrum Delta²(k) from sigma(M) namely the k_eff approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the tauCDM and LambdaCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (FKP) method. We find that the mass function based method presented here can provide a very accurate estimate of the linear power spectrum, particularly for low values of k. This estimate is comparable to, or even better behaved than, the FKP solution. The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution. ER - TY - Journal T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: luminosity and mass statistics A1 - Martínez, H. J. A1 - Zandivarez, A. A1 - Merchán, M. E. A1 - Domínguez, M. J. L. JO - Monthly Notices of the Royal Astronomical Society VL - 337 Y1 - 2002/12/1 SP - 1441 EP - 1449 KW - galaxies: clusters: general/ galaxies: luminosity function/ mass function/ galaxies: statistics UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.337.1441M&db_key=AST&high=42a068d47529002 N2 - Several statistics are applied to groups and galaxies in groups in the 2° Field Galaxy Redshift Survey. First, we estimate the luminosity functions for different subsets of galaxies in groups. The results are well fitted by a Schechter function with parameters M*- 5 log (h) =-19.90 +/- 0.03 and alpha=-1.13 +/- 0.02 for all galaxies in groups, which is quite consistent with the results of Norberg et al. for field galaxies. When considering the four different spectral types defined by Madgwick et al. we find that the characteristic magnitude is typically brighter than in the field. We also observe a steeper value, alpha=-0.76 +/- 0.03, of the faint end slope for low star-forming galaxies when compared with the corresponding field value. This steepening is more conspicuous, alpha=-1.10 +/- 0.06, for those galaxies in more massive groups than that obtained in the lower-mass subset, . Secondly, we compute group total luminosities using the prescriptions of Moore, Frenk & White. We define a flux-limited group sample using a new statistical tool developed by Rauzy. The resulting group sample is used to determine the group luminosity function and we find a good agreement with previous determinations and semi-analytical models. Finally, the group mass function for the flux-limited sample is derived. An excellent agreement is obtained when comparing our determination with analytical predictions over two orders of magnitude in mass. ER - TY - Journal T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: effects of environment on star formation A1 - Martínez, H. J. A1 - Zandivarez, A. A1 - Domínguez, M. A1 - Merchán, M. E. A1 - Lambas, D. G. JO - Monthly Notices of the Royal Astronomical Society VL - 333 Y1 - 2002/6/1 SP - L31 EP - L34 KW - galaxies: clusters: general/ galaxies: fundamental parameters/ galaxies: general/ galaxies: statistics/ galaxies: stellar content UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.333L..31M&db_key=AST&high=42a068d47529002 N2 - We estimate the fraction of star-forming galaxies in a catalogue of groups, constructed from the 2dF Galaxy Redshift Survey by Merchán & Zandivarez. We use the eta spectral type parameter of galaxies and subdivide the sample of galaxies in groups into four types depending on the values of the eta parameter following Madgwick et al. We obtain a strong correlation between the relative fraction of galaxies with high star formation and the parent group virial mass. We find that even in the environment of groups with low virial mass M~10¹³M_solar the star formation of their member galaxies is significantly suppressed. The relation between the fraction of early-type galaxies and the group virial mass obeys a simple power law spanning over three orders of magnitude in virial mass. Our results show quantitatively the way that the presence of galaxies with high star formation rates is inhibited in massive galaxy systems. ER - TY - Journal T1 - Quasar-Galaxy and AGN-Galaxy Cross-Correlations A1 - Martínez, Héctor J. A1 - Merchán, Manuel E. A1 - Valotto, Carlos A. A1 - Lambas, Diego G. JO - Astrophysical Journal VL - 514 Y1 - 1999/4/1 SP - 558 EP - 562 KW - GALAXIES: ACTIVE/ GALAXIES: CLUSTERS: GENERAL/ COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE/ GALAXIES: QUASARS: GENERAL UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...514..558M&db_key=AST&high=42a068d47529002 N2 - We compute quasar-galaxy and AGN-galaxy cross-correlation functions for samples taken from the Véron-Cetty & Véron catalog of quasars and active galaxies, using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The sample of active galaxy targets shows positive correlation at projected separations r_p<6 h^-1 Mpc consistent with the usual power law. On the other hand, we do not find a statistically significant positive quasar-galaxy correlation signal except in the range 3 h^-1 Mpclambda_max~1.8%, close to the polarization value produced by the ISM with normal efficiency (P_{lambda_max} ~ 5 E_B-V) with a color excess of E_B-V =0.51. Meanwhile for Hogg 22, located behind NGC 6204, the mean polarization is P_{lambda_max}~ 2.15%, lower than the expected value for the observed color excess of E_B-V =0.68 (Forbes et al. 1996) and the average efficiency of polarization for the interstellar dust. The mean angle of the polarization vectors of Hogg 22 is theta=44.9 °, which agrees with the expected angle produce by dust particles aligned in the direction of the Galactic Plane (theta=48^°), while for NGC 6204 a lower value, theta=33.7 °, was found. Therefore, we believe that Hogg 22 is depolarized by the same dust that is polarizing NGC 6204, due to different orientations of the dust particles (and magnetic fields) that polarize the starlight. Based on observations obtanined at Complejo Astronómico El Leoncito (CASLEO), operated under agreement between the CONICET and the National Universities of La Plata, Córdoba, and San Juan, Argentina. ER -