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 R1/4 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)~rho3/2T. 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⊙, 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 219deg and 316deg, 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 90deg sector centered at
l = 270deg. 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 = 270o and l = 0o, 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)⊙ =0.65 and M[V] = 4.84; the values (
{V-R)⊙ =0.37 and (V-I)⊙ =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
Dn-sigma and fundamental plane relations. We find that
about 12% of the galaxies are well represented by a pure r1/4
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 logDn, 0.064 dex for
logre, 0.086 mag arcsec-2 for
e>, and 0.09 for mRC,
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⊙ 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 ≈10-3 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-Msolar 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-Msolar Population I star with a
1.25-Msolar companion, and with period Pi= 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 MH ~ 2.3 x 10-6 Msun.
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-Msolar 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-Msolar 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 0.406Msolar. 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/Msolar<~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 Msolar 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 Msolar object that finally becomes a
helium white dwarf is modeled from Roche lobe detachment down to very
low luminosities (log L/Lsolar=-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
Msolar 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 0.161Msolar 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
0.41Msolar, 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/M≮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 M⊙ at
intervals of 0.05 M⊙ 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 M⊙ 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 M⊙ 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/L⊙) = -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/L⊙) = -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 Msun.
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 (≡ 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 Vsys~=-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 MHI~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 <= -25o
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 <= -25o. 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 Egamma >= 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 Te ~ 14 000 K and
Ne ~ 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 Te ~ 6,500 K and Ne ~ 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 JHKs 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 EB-V = 0.07 +/- 0.02
mag by means of the BVIC 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-MV = 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⊙. The IMF slopes for the most massive bins
yielded values of x ≈ 1.3 for NGC 2580 and x ≈ 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 EB-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 EB-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)_CHalpha
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
MV ~ +4.5, revealing that stars with MV < -2
are evolving off the main sequence; stars with -2 < MV
< +2 are located on the main sequence and stars with MV
> +2 are placed above it. According to our analysis, the cluster
distance is d = 2750 +/- 250 pc (V0-MV = 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 Msun 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
Halpha data, we detected nineteen stars with signs of
Halpha 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 < MV < 1.5 and from 3 to 80 {cal
Msun} 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 (Snu ∠nualpha) 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⊙ = 5.1 × 10-5 M⊙
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-47deg 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 Msun),
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-Msolar
neutron star and a normal, solar composition star of 2 Msolar
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 Msolar 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-1≲Gdot/G≲0,
whereas, for Gdot>0, the allowed values are
0≲Gdot/G≲4.0×10-11 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 */Msolar <=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 0.525Msolar ,
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^-6≮M_He/ M_*≮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
Msolar 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,Ms0) 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 MB=-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 (Lbulge/Ldisk) 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 Msun. 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, lg, bg, are
found to be: lg=0.°004+/-0.°039
bg=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 OmegaNep with k=4,5,... or
combined mean motion resonances with Uranus and Neptune of the form k
nN + j nU + 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_⊕ 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^Msun_, 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 2°x 2° 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 2°x 2° 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 Msolar yr-1
and M(WC5-7)=(4+/-2)×10-5 Msolar
yr-1], while a lower value was obtained for WC8-9 stars
[M(WC8-9)=(2+/-1)×10-5 Msolar
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 +24or 3866 and BD +25or 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
+24or 3866 (O8.5II(f)), BD +24or 3881 (O6.5III(f))
and BD +24or 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 +24or 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 +25or 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
Msun. The stellar winds of BD +24or 3866 and BD
+25or 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
Msun, respectively. The present observational data do not
allow us to identify a definite interstellar HI feature associated with
BD +24or 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 Msolar, 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 Msolar 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
Msolar, 180-500 cm-3 and ~90 Msolar 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 Msolar 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 Msolar appears to be related to the southern part
of the nebula, while 140+/-50 Msolar 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 Msolar, d=5 kpc) is associated
with the nebula, but the molecular material observed at 67 km
s-1 (~=70+/-25 Msolar, 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 (≡ST 2), WR 154 (≡HD 213049) and WR 155
(≡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⊙ (WR 126), 60
M⊙ (WR 155) and 85 M⊙ (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
(Snu~nualpha) 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
(Snu~nualpha) 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 Msolar and the rms electron
density at ~3 cm-3, assuming a homogeneous distribution. A
missing H I mass of 500 Msolar is obtained for the cavity and
an excess H I mass of 1500 Msolar 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 (Teff,log g, Mbol) 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 ≈ 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 ≈ 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-MV)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
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 MbJ
< -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
rp~ 1 h-1 Mpc for active galaxies and
rp~ 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 rp~ 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 bJ-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 bJ-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 ( ~ 8deg x 8deg),
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 Msolar. 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-Msolar 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 Msun 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: Ṗ=(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 13Msolar
(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 22-25Msolar we would derive for
the primary O3V a mass of `only' 52-60Msolar 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, Ap =
T⊥,p/T∥,p - 1 < 0 (T∥,
T⊥: 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 Ap, 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 (Dstmin < -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 Ks- 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 Ks- 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 OmegaCN 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 Msolar
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 (MV>~
1013.5 Msolar) 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(Lir)=10.7, lower than that
of interacting systems, log(Lir)=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 vLSR= +16.2
km s-1, has a linear size of about 7 pc, a mass of ~
104 M⊙ 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⊙ and the cloud volume density ~1200
cm-3. The analysis of the line ratios in this case revealed a
maximum of R2-1/1-0 = 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
(VLSR~-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 (VLSR~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 S1415 MHz=246 Jy and
S328 MHz=425 Jy, Sigma1
GHz~1.8×10-20 W m-2Hz-1
sr-1, and alpha=-0.35 (S~nualpha). 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_⊙, 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_⊙, 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, HV,
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 (Plambda_max ~ 5 EB-V) undergoing a
color excess of EB-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 Plambdamax=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 EB-V<0.45 for the first one and
EB-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
< MB <-18, with a peak at MB = - 22. The
magnitudes of the secondary components are in the range -22 <
MB < -16 with a maximum at MB = -19. Most pairs
have DeltaMB ~ 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 < Msecondary/Mprimary < 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 SN is 4.5+/-0.8, if a distance modulus
(V0-MV)=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
MWR/MOB.
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 (rp) 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 rp and DeltaV. We find that star formation in GPs is
significantly enhanced over that of isolated galaxies with similar
redshifts in the field for rp < 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 Ks. 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⊙ 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 SN=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 Msolar and then
falls off. The median mass is 0.30 Msolar. The current
population with masses greater than 0.4 Msolar 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 Msolar 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-Mv)=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 VOFblue= (-320 +/- 20)
kms-1 and VOFred= (+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
KS 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 Msolar. 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 MT= 1.5 ×
1010 Msolar 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 r1/4-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'' rmax~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.~80deg) is
practically perpendicular to the ouflow axis (at
P.A.~160deg). 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''
rmax~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 Teff=35,000 K, solar abundance, a range of
Te~6000-7000 K, and Ne~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
~Ldelta, 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~1013Msolar 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 MpcResorting Query Results for 2004A&A...419..965M
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 Tmin 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 Halpha_, 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
-4degdeg, |b|>20deg
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-dc relation for galaxy systems
at small dc. 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
Msolar ,
2×101314
Msolar, and
5×101314
Msolar, 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
Msolar 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 (Pg/Pe) vs. log Pe 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 Msolar
and ~16 Msolar and radii of ~10.1 Rsolar and ~8.4
Rsolar 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 13Msolar
(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 22-25Msolar we would derive for
the primary O3V a mass of `only' 52-60Msolar 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 34Msolar 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⊙, 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⊙ 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 Msolar 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
Pmax (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 Msolar, R1= 16.9
Rsolar for the O4f component and M2= 31.4
Msolar, R2= 13.8 Rsolar 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 Msolar, while its companion has
approximately 50 Msolar.
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 Rsun. The sizes and
masses are R1=11.53 +/- 0.5 Rsun,
M1=25.26 +/- 0.7 Msun, and R2=15.46 +/-
0.4 Rsun, M2=21.96 +/- 0.8 Msun 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 Msun, R1=14.9 +/- 0.4
Rsun, M2=18.4 +/- 0.7 {M}sun and
R_2=13.7 +/- 0.4 Rsun. 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+/-1.2Msolar,
R1=9.6+/-0.02Rsolar,
M2=27+/-1.2Msolar and
R2=8.0+/-0.05Rsolar. 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
Msun , R_1=15.54 +/- 0.4 Rsun , M_2=15.63 +/- 1.0
Msun and R_2=13.99 +/- 0.4 Rsun . 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 Msun to 0.5 Msun for the case of
helium core, from 0.45 Msun to 1.2 Msun for
carbon, oxygen and silicon cores, and from 0.45 Msun to 1.0
Msun 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
[MT_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-MV = 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-MT1 = 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-MV= 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-MV= 11.80 +/- 0.25 for logt= 9.15, and E(C-T1) =
0.23 +/- 0.07 and T1-MT1= 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 VIKC 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 ≃
Av ≃ 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 (Av
~ 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
AV~ 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, Mg=2.5
Msun and Mh=1.0 Msun, 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
Msolar. 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 Msolar. 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 Msolar, 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^Msun_ range. From the
event rate we have estimated a dark matter density
0.009<~rho_o_<~0.043hMsun_/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
keff 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 0.169Msolar 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
0.3Msolar can reach the turn-off in their colours and become
blue again within cooling times much less than 15Gyr and then remain
brighter than MV~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 0.169Msolar 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
0.3Msolar can reach the turn-off in their colours and become
blue again within cooling times much less than 15Gyr and then remain
brighter than MV~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 0h <= RA <= 24h 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)~Lalpha, 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 ≈
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 ≈ 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 Msolar. 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 Msun ) 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
2000Msun_ 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
50Msun_ 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 600Msun_.
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 Msolar 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
Msolar, 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 Msun 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: Ṗ=(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-Mv)=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
keff 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~1013Msolar 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 (Plambda_max
~ 5 EB-V) with a color excess of EB-V =0.51.
Meanwhile for Hogg 22, located behind NGC 6204, the mean polarization is
Plambda_max~ 2.15%, lower than the expected value for
the observed color excess of EB-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 -