TY - Journal
T1 - Mass-radius relations for massive white dwarf stars
A1 - Althaus, L. G.
A1 - García-Berro, E.
A1 - Isern, J.
A1 - Córsico, A. H.
JO - Astronomy and Astrophysics
VL - 441
Y1 - 2005/10/1
SP - 689
EP - 694
KW - stars: evolution/ stars: white dwarfs/ stars:/ fundamental parameters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...441..689A&db_key=AST&high=42a068d47501191
N2 - We present detailed theoretical mass-radius relations for massive white
dwarf stars with oxygen-neon cores. This work is motivated by recent
observational evidence about the existence of white dwarf stars with
very high surface gravities. Our results are based on evolutionary
calculations that take into account the chemical composition expected
from the evolutionary history of massive white dwarf progenitors. We
present theoretical mass-radius relations for stellar mass values
ranging from 1.06 to 1.30 M⊙ with a step of 0.02
M⊙ and effective temperatures from 150 000 K to ≈5000
K. A novel aspect predicted by our calculations is that the mass-radius
relation for the most massive white dwarfs exhibits a marked dependence
on the neutrino luminosity. Extensive tabulations for massive white
dwarfs, accessible from our web site, are presented as well.
ER -
TY - Journal
T1 - The formation of DA white dwarfs with thin hydrogen envelopes
A1 - Althaus, L. G.
A1 - Miller Bertolami, M. M.
A1 - Córsico, A. H.
A1 - García-Berro, E.
A1 - Gil-Pons, P.
JO - Astronomy and Astrophysics
VL - 440
Y1 - 2005/9/1
SP - L1
EP - L4
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=2005A%26A...440L...1A&db_key=AST&high=42a068d47501191
N2 - We study the formation and evolution of DA white dwarfs, the progenitors
of which have experienced a late thermal pulse (LTP) shortly after the
departure from the thermally pulsing AGB. To this end, we compute the
complete evolution of an initially 2.7~M⊙ star all the
way from the zero-age main sequence to the white dwarf stage. We find
that most of the original H-rich material of the post-AGB remnant is
burnt during the post-LTP evolution, with the result that, at entering
its white dwarf cooling track, the remaining H envelope becomes
10-6~M⊙ in agreement with asteroseismological
inferences for some ZZ Ceti stars.
ER -
TY - Journal
T1 - Can pulsating PG 1159 stars place constraints on the occurrence of core overshooting?
A1 - Córsico, A. H.
A1 - Althaus, L. G.
JO - Astronomy and Astrophysics
VL - 439
Y1 - 2005/9/1
SP - L31
EP - L34
KW - stars: evolution/ stars: interiors/ stars:/ white dwarfs/ stars: oscillations/ stars: convection
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...439L..31C&db_key=AST&high=42a068d47501191
N2 - The present letter is aimed at exploring the influence of overshooting
during the central helium burning in pre-white dwarf progenitors on the
pulsational properties of PG 1159 stars. To this end we follow the
complete evolution an intermediate-mass white dwarf progenitor from the
zero age main sequence through the thermally pulsing and born-again
phases to the domain of the PG 1159 stars. Our results suggest that the
presence of mode-trapping features in the period spacings of these hot
pulsating stars could result from structure in the carbon-oxygen core.
We find in particular that in order to get enough core structure
consistent with observational demands, the occurrence of overshoot
episodes during the central helium burning is needed. This conclusion is
valid for thick helium envelopes like those predicted by our detailed
evolutionary calculations. If the envelope thickness were substantially
smaller, then the occurrence of core overshooting would be more
difficult to disentangle from the effects related to the envelope
transition zones.
ER -
TY - Journal
T1 - On the excitation of PG 1159-type pulsations
A1 - Gautschy, A.
A1 - Althaus, L. G.
A1 - Saio, H.
JO - Astronomy and Astrophysics
VL - 438
Y1 - 2005/8/1
SP - 1013
EP - 1020
KW - stars: evolution/ stars: white dwarfs/ stars: oscillations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...438.1013G&db_key=AST&high=42a068d47501191
N2 - Stability properties are presented of dipole
and quadrupole nonradial oscillation modes of model stars
that experienced a late helium shell flash on their way to
the white-dwarf cooling domain. The computed instability
domains are compared with the observed hot variable central
stars of planetary nebulae and the GW Vir pulsators.
ER -
TY - Journal
T1 - The formation and evolution of hydrogen-deficient post-AGB white dwarfs: The emerging chemical profile and the expectations for the PG 1159-DB-DQ evolutionary connection
A1 - Althaus, L. G.
A1 - Serenelli, A. M.
A1 - Panei, J. A.
A1 - Córsico, A. H.
A1 - García-Berro, E.
A1 - Scóccola, C. G.
JO - Astronomy and Astrophysics
VL - 435
Y1 - 2005/5/1
SP - 631
EP - 648
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=2005A%26A...435..631A&db_key=AST&high=42a068d47501191
N2 - We explore the formation and evolution of hydrogen-deficient post-AGB
white dwarfs. To this end, we compute the complete evolution of an
initially 2.7 ~M⊙ star from the zero-age main sequence
through the thermally pulsing and mass-loss phases to the white dwarf
stage. Particular attention is given to the chemical abundance changes
during the whole evolution. A time-dependent scheme for the simultaneous
treatment of abundance changes caused by nuclear reactions, diffusive
overshooting, salt fingers and convection is considered. We employed the
double-diffusive mixing-length theory of convection for fluids with
composition gradients. The study can therefore be considered as a test
of its performance in low-mass stars. Also, time-dependent element
diffusion for multicomponent gases is taken into account during the
white dwarf evolution. The evolutionary stages corresponding to the last
helium thermal pulse on the early white-dwarf cooling branch and the
following born-again episode are carefully explored. Relevant aspects
for PG 1159 stars and DB white dwarf evolution are studied in the
framework of these new evolutionary models that take into account the
history of the white dwarf progenitor. The scope of the calculations is
extended to the domain of the helium-rich, carbon-contaminated DQ white
dwarfs with the aim of exploring the plausibility of the evolutionary
connection PG 1159-DB-DQ. In this regard, the implications for the
double-layered chemical structure in pulsating DB white dwarfs is
investigated. We examine the consequences of mass-loss episodes during
the PG 1159 stage for the chemical stratification of the outer layer of
DB and DQ white dwarfs.
ER -
TY - Journal
T1 - New evolutionary models for massive ZZ Ceti stars. II. The effects of crystallization on their pulsational properties
A1 - Córsico, A. H.
A1 - Althaus, L. G.
A1 - Montgomery, M. H.
A1 - García-Berro, E.
A1 - Isern, J.
JO - Astronomy and Astrophysics
VL - 429
Y1 - 2005/1/1
SP - 277
EP - 290
KW - dense matter/ stars: evolution/ stars: white dwarfs/ stars: oscillations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...429..277C&db_key=AST&high=42a068d47501191
N2 - In view of recent claims that asteroseismology could supply invaluable
insight into the crystallization process occurring in the interiors of
massive white dwarf stars, we present in this work new pulsational
calculations for improved carbon-oxygen DA white dwarf models suitable
for the study of massive ZZ Ceti stars. The background models employed
in this study, presented in detail in a recent paper by Althaus et al.
(\cite{Althaus2003}, A&A, 404, 593), are the result of the complete
evolution of massive white dwarf progenitors from the zero-age main
sequence through the Asymptotic Giant Branch (AGB) and mass loss phases
to the white dwarf regime. Abundance changes are accounted for by means
of a full coupling between nuclear evolution and time-dependent mixing
due to convection, salt fingers, and diffusive overshoot. In addition,
time-dependent element diffusion for multicomponent gases has been
considered during the white dwarf evolution. Crystallization and
chemical rehomogenization due to phase separation upon crystallization
in the core of our models have been fully considered. The effects of
crystallization on the period spectrum of these massive white dwarf
models are assessed by means of a detailed pulsational analysis of
linear, nonradial, adiabatic gravity modes. To properly account for the
effects of the presence of a solid phase in the models we impose special
conditions on the oscillation eigenfunctions at the solid-liquid
interface. We find that the theoretical pulsation spectrum is strongly
modified when crystallization is considered, in particular concerning
the mode trapping properties of the equilibrium models. We show that the
strong mode trapping seen in the models with overshooting can be
reproduced by means of a simple analytical model. We also discuss at
some length the implications of our study for BPM 37093, the most
massive ZZ Ceti star presently known. In particular, we attempt to place
constraints on the physical processes occurring prior to the formation
of this white dwarf. We find that if BPM 37093 has a stellar mass of
≈1.00 M⊙, its observed spectrum could bear the
signature of overshoot episodes during the helium core burning.
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=42a068d47501191
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=42a068d47501191
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 - Representation of the International Celestial Reference System (ICRS) by different sets of selected radio sources
A1 - Arias, E. F.
A1 - Bouquillon, S.
JO - Astronomy and Astrophysics
VL - 422
Y1 - 2004/8/1
SP - 1105
EP - 1108
KW - reference systems/ techniques: interferometric
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...422.1105A&db_key=AST&high=42a068d47501191
N2 - To contribute to the maintenance and extension of the ICRF, we have
studied representations of the ICRS by different sets of selected radio
sources. The axes of the ICRS are realized by the coordinates of 212
sources in the ICRF qualified as the ``defining'' objects of the frame.
They have been selected by the WGRF of the IAU by applying quality
criteria to VLBI observations from 1975-1995. A different selection of
sources has been proposed by Feissel-Vernier based on an analysis of
time series of radio source coordinates over the period 1989-2002. We
compare the quality of the realization of the ICRS by the two sets of
selected sources.
ER -
TY - Journal
T1 - Testing the internal physics of white dwarfs from their pulsational properties
A1 - Isern, J.
A1 - Garcia-Berro, E.
A1 - Corsico, A. H.
A1 - Benvenuto, O. G.
A1 - Althaus, L. G.
JO - Communications in Asteroseismology
VL - 145
Y1 - 2004/6/1
SP - 13
EP - 15
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004CoAst.145...13I&db_key=AST&high=42a068d47501191
N2 - White dwarfs are well studied objects. The relative simplicity of their
physics allows to obtain very detailed models which can be ultimately
compared with their observed properties. Among white dwarfs there is a
specific class of stars, known as ZZ-Ceti objects, which have a
hydrogen-rich envelope and show periodic variations in their light
curves. The rate of change of the period is closely related to the
star's 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. 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 - The Second Extension of the International Celestial Reference Frame: ICRF-EXT.1
A1 - Fey, A. L.
A1 - Ma, C.
A1 - Arias, E. F.
A1 - Charlot, P.
A1 - Feissel-Vernier, M.
A1 - Gontier, A.-M.
A1 - Jacobs, C. S.
A1 - Li, J.
A1 - MacMillan, D. S.
JO - Astronomical Journal
VL - 127
Y1 - 2004/6/1
SP - 3587
EP - 3608
KW - Astrometry/ Catalogs/ Galaxies: Quasars: General/ Radio Continuum: Galaxies/ Reference Systems/ Techniques: Interferometric
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127.3587F&db_key=AST&high=42a068d47501191
N2 - We use very long baseline interferometry data obtained between mid-1995
and the end of 2002 May together with older data to extend and revise
the International Celestial Reference Frame (ICRF). Revised positions of
ICRF candidate and ``other'' sources, based on inclusion of the
additional data, are presented. Positions, in the frame of the ICRF, for
an additional 109 new sources are also presented. All but four of the
new sources are located north of delta=-30°. Positions of the ICRF
defining sources remain unchanged. We present a summary of current
astrometric and geodetic observing programs and discuss the evolution
and future of the ICRF.
ER -
TY - Journal
T1 - Mass distribution of DA white dwarfs in the First Data Release of the Sloan Digital Sky Survey
A1 - Madej, J.
A1 - Nalezyty, M.
A1 - Althaus, L. G.
JO - Astronomy and Astrophysics
VL - 419
Y1 - 2004/5/1
SP - L5
EP - L8
KW - catalogs/ stars: fundamental parameters/ stars: white dwarfs
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...419L...5M&db_key=AST&high=42a068d47501191
N2 - We investigate the sample of 1175 new nonmagnetic DA white dwarfs with
the effective temperatures TMSUB>eff ≥12 000 K, which were
extracted from the Data Release 1 of the Sloan Digital Sky Survey. We
determined masses, radii, and bolometric luminosities of stars in the
sample. The above parameters were derived from the effective
temperatures Teff and surface gravities log g published in
the DR1, and the new theoretical M-R relations for carbon-core and
oxygen-core white dwarfs. Mass distribution of white dwarfs in this
sample exhibits the peak at M=0.562 M⊙ (carbon-core
stars), and the tail towards higher masses. Both the shape of the mass
distribution function and the empirical mass-radius relation are
practically identical for white dwarfs with either pure carbon or pure
oxygen cores.
ER -
TY - Journal
T1 - The Globular Cluster System of NGC 1399. III. VLT Spectroscopy and Database
A1 - Dirsch, B.
A1 - Richtler, T.
A1 - Geisler, D.
A1 - Gebhardt, K.
A1 - Hilker, M.
A1 - Alonso, M. V.
A1 - Forte, J. C.
A1 - Grebel, E. K.
A1 - Infante, L.
A1 - Larsen, S.
A1 - Minniti, D.
A1 - Rejkuba, M.
JO - Astronomical Journal
VL - 127
Y1 - 2004/4/1
SP - 2114
EP - 2132
KW - Cosmology: Dark Matter/ Galaxies: Elliptical and Lenticular/ cD/ Galaxies: Halos/ Galaxies: Individual: NGC Number: NGC 1399/ Galaxies: Kinematics and Dynamics/ Galaxies: Star Clusters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127.2114D&db_key=AST&high=42a068d47501191
N2 - Radial velocities of 468 globular clusters around NGC 1399, the central
galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask
Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest
sample of globular cluster velocities around any galaxy obtained so far.
The mean velocity uncertainty is 50 km s-1. This data sample
is accurate and large enough to be used in studies of the mass
distribution of NGC 1399 and the properties of its globular cluster
system. Here we describe the observations and the reduction procedure,
and we discuss the uncertainties of the resulting velocities. The
complete sample of cluster velocities that is used in a dynamical study
of NGC 1399 is tabulated. A subsample is compared with previously
published values.
Based on observations collected at the European Southern Observatory,
Cerro Paranal, Chile; ESO program 66.B-0393.
ER -
TY - Journal
T1 - The Globular Cluster System of NGC 1399. II. Kinematics of a Large Sample of Globular Clusters
A1 - Richtler, T.
A1 - Dirsch, B.
A1 - Gebhardt, K.
A1 - Geisler, D.
A1 - Hilker, M.
A1 - Alonso, M. V.
A1 - Forte, J. C.
A1 - Grebel, E. K.
A1 - Infante, L.
A1 - Larsen, S.
A1 - Minniti, D.
A1 - Rejkuba, M.
JO - Astronomical Journal
VL - 127
Y1 - 2004/4/1
SP - 2094
EP - 2113
KW - Cosmology: Dark Matter/ Galaxies: Elliptical and Lenticular/ cD/ Galaxies: Halos/ Galaxies: Individual: NGC Number: NGC 1399/ Galaxies: Kinematics and Dynamics/ Galaxies: Star Clusters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127.2094R&db_key=AST&high=42a068d47501191
N2 - We study the kinematics and dynamics of the globular cluster system of
NGC 1399, the brightest elliptical galaxy near the center of the Fornax
cluster of galaxies. The observational data consists of
medium-resolution spectra, obtained at the Very Large Telescope with
FORS2 and the Mask Exchange Unit (MXU). Our sample comprises 468 radial
velocities in the magnitude range 20R<23. This is the
largest sample of globular cluster velocities around any galaxy obtained
so far. Typical velocity uncertainties are 50 km s-1,
significantly improving on earlier samples. The radial range is
2'', corresponding to 11 kpc to 50 kpc
of galactocentric distance. The shape of the velocity distribution of
the sample is compatible with being a Gaussian distribution. However,
under moderate error selection, a slight asymmetry is visible between
high and low radial velocities. We find bright clusters with radial
velocities below 800 km s-1, while they are not found at the
corresponding high-velocity side above 2000 km s-1. There is
the possibility that unbound clusters and/or objects in the foreground
contaminate the NGC 1399 cluster sample. Under strong error selection,
practically no objects are found with velocities lower than 800 km
s-1 or higher than 2000 km s-1. Since the extreme
velocities influence the velocity dispersion considerably, uncertainty
regarding the exact value of the dispersion remains. With the above
velocity limits, we derive a projected velocity dispersion for the total
sample of 274+/-9 km s-1 which within the uncertainties
remains constant over the entire radial range. Without any velocity
restriction, it increases to 325 km s-1. Guided by the
bimodal color distribution of clusters, we distinguish between red
clusters (C-R>1.6) and blue clusters (C-R<1.6), and find velocity
dispersions for these groups of 255+/-13 and 291+/-14 km s-1,
respectively, again radially constant. Any possible rotation of either
of these cluster populations is below the detection limit, with the
exception of a weak signature of rotation for the blue clusters more
distant than 6'. Spherical models point to a circular velocity of
419+/-30 km s-1, assuming isotropy for the red clusters. This
value is constant out to 40 kpc. The inferred dark halo potential can be
well represented by a logarithmic potential. A halo of the NFW type also
provides a good fit to the observations. The orbital structure of the
clusters can only be weakly constrained. It is consistent with isotropy
for the red clusters and a slight tangential bias for the blue clusters.
Some mass profiles derived from X-ray analyses do not agree with a
constant circular velocity within our radial range, irrespective of its
exact value. Interpreting the extreme low radial velocities as space
velocities of bound clusters near their pericentric distances would
require an extension of the cluster system of at least 200 kpc.
Implications for formation scenarios of the cluster system are briefly
commented on.
Based on observations collected at the European Southern Observatory,
Cerro Paranal, Chile; ESO program 66.B-0393.
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=42a068d47501191
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=42a068d47501191
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 - Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
A1 - Wegner, G.
A1 - Bernardi, M.
A1 - Willmer, C. N. A.
A1 - da Costa, L. N.
A1 - Alonso, M. V.
A1 - Pellegrini, P. S.
A1 - Maia, M. A. G.
A1 - Chaves, O. L.
A1 - Rité, C.
JO - Astronomical Journal
VL - 126
Y1 - 2003/11/1
SP - 2268
EP - 2280
KW - Galaxies: Distances and Redshifts/ Galaxies: Elliptical and Lenticular/ cD/ Galaxies: General/ Cosmology: Large-Scale Structure of Universe/ Surveys/ Techniques: Spectroscopic
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....126.2268W&db_key=AST&high=42a068d47501191
N2 - We present central velocity dispersions and Mg2 line indices
for an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984
had no previous measures. This sample contains the largest set of
homogeneous spectroscopic data for a uniform sample of elliptical
galaxies in the nearby universe. These galaxies were observed as part of
the ENEAR project, designed to study the peculiar motions and internal
properties of the local early-type galaxies. Using 523 repeated
observations of 317 galaxies obtained during different runs, the data
are brought to a common zero point. These multiple observations, taken
during the many runs and different instrumental setups employed for this
project, are used to derive statistical corrections to the data and are
found to be relatively small, typically <~5% of the velocity
dispersion and 0.01 mag in the Mg2 line strength. Typical
errors are about 8% in velocity dispersion and 0.01 mag in
Mg2, in good agreement with values published elsewhere.
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=42a068d47501191
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 - Oscillations of Short Periods in Neutron and Strange Stars
A1 - Losada, Edith L.
A1 - Aquilano, Roberto O.
JO - General Relativity and Gravitation
VL - 35
Y1 - 2003/8/1
SP - 1385
EP - 1398
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GReGr..35.1385L&db_key=AST&high=42a068d47501191
N2 - We present a model of a remnant of supernova, and we analyze the
correlation with the observational data to short periods oscillations
between a neutron star and a strange matter star. The results confirm
previous conclusions.
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=42a068d47501191
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 - 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=42a068d47501191
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 - Astrophysics of Radiating Shells
A1 - Monton, Carlos
A1 - Scancich, Miriam
A1 - Aquilano, Roberto
JO - Astronomical and Astrophysical Transactions
VL - 22
Y1 - 2003/3/1
SP - 357
EP - 361
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26AT...22..357M&db_key=AST&high=42a068d47501191
N2 - A seminumerical 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 - On the ages of exoplanet host stars
A1 - Saffe, C.
A1 - Gómez, M.
A1 - Chavero, C.
JO - Astronomy and Astrophysics
VL - 443
Y1 - 2005/11/1
SP - 609
EP - 626
KW - stars: chromospheres/ stars: fundamental parameters/ stars: kinematics/ stars: planetary systems/ techniques: spectroscopic
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...443..609S&db_key=AST&high=42a068d47516201
N2 - We obtained spectra, covering the CaII H and K region, for 49 exoplanet
host (EH) stars, observable from the southern hemisphere. We measured
the chromospheric activity index, R'{_HK}. We compiled previously
published values of this index for the observed objects as well as the
remaining EH stars in an effort to better smooth temporal variations and
derive a more representative value of the average chromospheric activity
for each object. We used the average index to obtain ages for the group
of EH stars. In addition we applied other methods, such as: Isochrone,
lithium abundance, metallicity and transverse velocity dispersions, to
compare with the chromospheric results. The kinematic method is a less
reliable age estimator because EH stars lie red-ward of Parenago's
discontinuity in the transverse velocity dispersion vs dereddened B-V
diagram. The chromospheric and isochrone techniques give median ages of
5.2 and 7.4 Gyr, respectively, with a dispersion of 4 Gyr. The median
age of F and G EH stars derived by the isochrone technique is 1-2 Gyr
older than that of identical spectral type nearby stars not known to be
associated with planets. However, the dispersion in both cases is large,
about 2-4 Gyr. We searched for correlations between the chromospheric
and isochrone ages and L_IR/L* (the excess over the stellar
luminosity) and the metallicity of the EH stars. No clear tendency is
found in the first case, whereas the metallicy dispersion seems to
slightly increase with age.
ER -
TY - Journal
T1 - The neutral gas in the environs of the Geminga gamma-ray pulsar
A1 - Giacani, E.
A1 - Reynoso, E. M.
A1 - Dubner, G.
A1 - Goss, W. M.
A1 - Green, A. J.
A1 - Johnston, S.
JO - Advances in Space Research
VL - 35
Y1 - 2005/1/1
SP - 1070
EP - 1073
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AdSpR..35.1070G&db_key=AST&high=42a068d47516201
N2 - We present a high-resolution (24") study of the HI interstellar
gas distribution around the radio-quiet neutron star Geminga. Based on
very large array and MPIfR Effelsberg telescope data, we analyzed a
40' × 40' field around Geminga. These observations
have revealed the presence of a neutral gas shell, 0.4 pc in radius,
with an associated HI mass of 0.8M⊙, which surrounds
Geminga at a radial velocity compatible with the kinematical distance of
the neutron star. In addition, morphological agreement is observed
between the internal face of the HI shell and the brightest structure of
Geminga's tail observed in X-rays. We explore the possibility that
this morphological agreement is the result of a physical association.
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=42a068d47516201
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 - A search for disks around exoplanet host stars
A1 - Saffe, C.
A1 - Gómez, M.
JO - Astronomy and Astrophysics
VL - 423
Y1 - 2004/8/1
SP - 221
EP - 233
KW - stars: circumstellar matter/ stars: planetary systems/ technique: photometry/ technique: polarimetry/ stars: planetary systems: formation
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...423..221S&db_key=AST&high=42a068d47516201
N2 - We have assembled a database which comprises optical and infrared (IR)
photometry of Exoplanet Host stars (EHs), and constructed the spectral
energy distributions (SEDs) of these stars. We use several quantities to
explore the existence of excess IR emission with respect to the
photospheric level. In particular, the criteria proposed by \citet{mb}
identify IR excess in 19-23% of the class V EH sources (i.e., in 6-7 out
of 31). Several searches for Vega-like systems have yielded a similar
fraction of objects with IR excess emission among main sequence stars.
This excess emission is likely due to the presence of dust in
circumstellar disks. We compare the optical polarization properties of
the EHs, Vega-like candidate objects and pre-main sequence stars. While
the median polarizations of the EHs and Vega-like candidate objects are
very similar, both groups have significant lower median optical
polarization values than T Tauri and Herbig AeBe stars.
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=42a068d47516201
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 - The neutral gas in the environs of the Wolf Rayet stars in the Circinus OB1 association
A1 - Giacani, E.
A1 - Dubner, G.
JO - Astronomy and Astrophysics
VL - 413
Y1 - 2004/1/1
SP - 225
EP - 231
KW - ISM: general/ stars: individual: WR 65/ stars: individual: WR 67/ stars: Wolf-Rayet
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...413..225G&db_key=AST&high=42a068d47516201
N2 - We have investigated the neutral hydrogen in the direction of the
Circinus OB1 association with particular emphasis in the study of the
vicinity of the WR stars WR 65 and WR 67. The HI line data were obtained
with the Australia Telescope Compact Array with a synthesized beam of
4\farcm0 × 2\farcm7 and a velocity resolution of 1.1 km
s-1. These data led to the discovery of a large cavity
surrounded by an almost complete shell in agreement with the locations
and distances of the two WR stars. We propose that the HI features
constitute an interstellar bubble created by the powerful winds of the
WR stars and their progenitors. By assuming a distance of 3 kpc, we
calculate for this HI bubble a linear radius of 22 pc, a swept-up mass
of 1600 M_⊙ and an expansion velocity of more than 7 km
s-1. High angular resolution IRAS infrared data (HIRES)
reveal the presence of a ring with good spatial correlation with the HI
shell. Eight IRAS protostellar candidates located around the HI cavity
suggest that star formation may be taking place in the shell. Further
investigation is required to confirm this proposition.
ER -
TY - Journal
T1 - Young Brown Dwarfs in the Chamaeleon Cloud Complex
A1 - Persi, Paolo
A1 - Gòmez, Mercedes
JO - Baltic Astronomy
VL - 13
Y1 - 2004/1/1
SP - 500
EP - 504
KW - stars: formation/ stars: low-mass/ brown dwarfs/ infrared: stars
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004BaltA..13..500P&db_key=AST&high=42a068d47516201
N2 - We present the results of ISOCAM observations at 6.75 and 14.3 mu m,
and near-IR spectra of a selected sample of candidate young brown dwarfs
and very low-mass young stellar objects in the Chamaeleon dark cloud
complex. We confirm the object Cha Halpha 1 (ISO-Cha I 95) as a bona
fide young brown dwarf and identify four new young objects in Cha I
(ISO-Cha I 138, 143, 235 and 250) with spectral types {\msf ≥} M6 and
masses close to the hydrogen burning limit. Another new candidate young
sub-stellar system has been detected in the core of the Cha II dark
cloud (ISO-Cha II 13). All these sources show significant mid-IR
excesses probably due to the presence of circumstellar disks.
ER -
TY - Journal
T1 - Optical spectra of selected Chamaeleon I young stellar objects
A1 - Saffe, C.
A1 - Gómez, M.
A1 - Randich, S.
A1 - Mardones, D.
A1 - Caselli, P.
A1 - Persi, P.
A1 - Racca, G.
JO - Astronomy and Astrophysics
VL - 409
Y1 - 2003/10/1
SP - 993
EP - 1005
KW - 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=2003A%26A...409..993S&db_key=AST&high=42a068d47516201
N2 - We present optical spectra of eight candidate brown dwarfs and a
previously known T Tauri star (Sz 33) of the Chamaeleon I dark cloud. We
derived spectral types based on the strength of the TiO or VO absorption
bands present in the spectra of these objects as well as on the PC3
index of \cite{mar99}. Photometric data from the literature are used to
estimate the bolometric luminosities for these sources. We apply
\cite{dama97} pre-main sequence evolutionary tracks and isochrones to
derive masses and ages. Based on the presence of Halpha in emission,
we confirm that most of the candidates are young objects. Our sample
however includes two sources for which we can only provide upper limits
for the emission in Halpha ; whereas these two objects are most likely
foreground/background stars, higher resolution spectra are required to
confirm their true nature. Among the likely cloud members, we detect one
new sub-stellar object and three transition stellar/sub-stellar sources.
Based on observations collected at the European Southern Observatory,
Chile, (ESO proposal 67.C-00365).
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=42a068d47516201
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 - Spectroscopic orbits of two short-period early-type binaries using two-dimensional cross-correlations
A1 - González, J. F.
A1 - Lapasset, E.
JO - Astronomy and Astrophysics
VL - 404
Y1 - 2003/6/1
SP - 365
EP - 372
KW - techniques: radial velocities/ binaries: spectroscopic/ stars: individual: HD 66066A/ HD 315031/ open clusters and associations: individual: NGC 2516/ NGC 6530
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...404..365G&db_key=AST&high=42a068d47516201
N2 - We apply the two-dimensional cross-correlation technique TODCOR to
derive spectroscopic orbits for the two B-type double-lined
spectroscopic binaries HD 66066A and HD
315031, previously mentioned as blue straggler candidates of
the open clusters NGC 2516 and NGC
6530, respectively. Reliable radial velocities for both
components are measured even for orbital phases for which the separation
between the spectral lines are about 0.5 times the quadratic sum of the
full-width at half-maximum of the lines. Both binaries have circular
orbits and the orbital periods are 1.67 and 1.38 days for HD 66066A and
HD 315031, respectively. We calculate minimum masses with errors of 3-5%
and obtain the projected radii from the line widths. We derive absolute
stellar parameters which are consistent with the age and distance of the
clusters. Both binary systems are formed by main-sequence stars and it
is expected that they will experience mass-transfer between their
components before the end of the core H-burning stage. HD 315031 is
likely a triple system as suggested by the variation of the
center-of-mass velocity.
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 - 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=42a068d47516201
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 and ISOCAM observations of the Chamaeleon II dark cloud
A1 - Persi, P.
A1 - Marenzi, A. R.
A1 - Gómez, M.
A1 - Olofsson, G.
JO - Astronomy and Astrophysics
VL - 399
Y1 - 2003/3/1
SP - 995
EP - 1002
KW - stars: formation/ stars: low-mass/ brown dwarfs/ stars: pre-main sequence/ infrared: stars
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...399..995P&db_key=AST&high=42a068d47516201
N2 - An infrared study including ISOCAM images at 6.75 and 14.3 mu m of a
large portion (28 arcmin x 26 arcmin) of the Chamaeleon II dark cloud
and sub-arcsec resolution JHKs images of the central (4.9
arcmin x 4.9 arcmin) area is presented. Combining the ISOCAM
observations with J and Ks photometry obtained with DENIS, we
have found 12 young stars, of which 8 are previously identified sources.
Of the new candidate YSOs, ISO-ChaII13 shows a clear mid-IR excess with
an infrared luminosity of ~ 0.02 Lsun and a stellar
luminosity >=0.01 Lsun. This last value of luminosity
corresponds to that expected for a sub-stellar object with an age
between 1-10 Myr. The analysis of the J-H/H-K diagram of the sources
detected in the central part of the dark cloud has allowed us to
identify 10 very faint sources not found by ISOCAM with possible near-IR
excesses that may be embedded young brown dwarfs. Finally, the center of
the dark cloud is characterized by the presence of the Class I YSO IRAS
12553-7651 (ISO-ChaII28) with Lbol= 1.49 Lsun, and
associated with a faint nebulosity observed at 2.2 mu m.
Based on observations collected at the European Southern Observatory,
Chile, ESO proposal N.65.I-0054, CTIO(Chile), and ISOCAM observations
N.11500619, and 11500620.
Tables 1 and 2 are only available in electronic at the CDS via anonymous
ftp to cdsarc.u-strasbg.fr (130.79.125.5) or via
http:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/995
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=42a068d47516201
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 - Flows in the solar atmosphere due to the eruptions on the 15th July, 2002
A1 - Harra, L. K.
A1 - Démoulin, P.
A1 - Mandrini, C. H.
A1 - Matthews, S. A.
A1 - van Driel-Gesztelyi, L.
A1 - Culhane, J. L.
A1 - Fletcher, L.
JO - Astronomy and Astrophysics
VL - 438
Y1 - 2005/8/1
SP - 1099
EP - 1106
KW - Sun: flares/ Sun: UV radiation/ Sun: corona/ Sun: coronal mass ejections (CMEs)
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...438.1099H&db_key=AST&high=42a068d47519878
N2 - Which kind of flows are present during flares? Are they compatible with
the present understanding of energy release and which model best
describes the observations? We analyze successive flare events in order
to answer these questions. The flares were observed in the magnetically
complex NOAA active region (AR) 10030 on 15 July 2002. One of them is of
GOES X-class. The description of these flares and how they relate to the
break-out model is presented in Gary & Moore (2004). The Coronal
Diagnostic Spectrometer on board SOHO observed this active region for
around 14 h. The observed emission lines provided data from the
transition region to the corona with a field of view covering more than
half of the active region. In this paper we analyse the spatially
resolved flows seen in the atmosphere from the preflare to the flare
stages. We find evidence for evaporation occurring before the impulsive
phase. During the main phase, the ongoing magnetic reconnection is
demonstrated by upflows located at the edges of the flare loops (while
downflows are found in the flare loops themselves). We also report the
impact of a filament eruption on the atmosphere, with flows up to 300 km
s-1 observed at transition-region temperatures in regions
well away from the location of the pre-eruptive filament. Our results
are consistent with the predictions of the break out model before the
impulsive phase of the flare; while, as the flare progresses, the
directions of the flows are consistent with flare models invoking
evaporation followed by cooling and downward plasma motions in the flare
loops.
ER -
TY - Journal
T1 - Infrared mergers and infrared quasi-stellar objects with galactic winds - III. Mrk 231: an exploding young quasi-stellar object with composite outflow/broad absorption lines (and multiple expanding superbubbles)
A1 - Lípari, S.
A1 - Terlevich, R.
A1 - Zheng, W.
A1 - Garcia-Lorenzo, B.
A1 - Sanchez, S. F.
A1 - Bergmann, M.
JO - Monthly Notices of the Royal Astronomical Society
VL - 360
Y1 - 2005/6/1
SP - 416
EP - 446
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.360..416L&db_key=AST&high=42a068d47519878
N2 - We present a study of outflow (OF) and broad absorption line (BAL)
systems in Mrk 231, and in similar infrared (IR) quasi-stellar objects
(QSOs). This study is based mainly on one-dimensional and
two-dimensional spectroscopy (obtained at La Palma/William Herschel
Telescope, Hubble Space Telescope, International Ultraviolet Explorer,
European Southern Observatory/New Technology Telescope, Kitt Peak
National Observatory, Apache Point Observatory and Complejo Astronomico
El Leoncito observatories) plus Hubble Space Telescope images. For Mrk
231, we report evidence that the extreme nuclear OF process has at least
three main components on different scales, which are probably associated
with: (i) the radio jet, at parsec scale; (ii) the extreme starburst at
parsec and kiloparsec scale. This OF has generated at least four
concentric expanding superbubbles and the BAL systems.
Specifically, inside and very close to the nucleus the two-dimensional
spectra show the presence of an OF emission bump in the blend
Halpha+[NII], with a peak at the same velocity of the main BAL-I
system (VEjectionBAL-I~-4700 km s-1). This bump
was more clearly detected in the area located at 0.6-1.5 arcsec
(490-1220 pc), to the south-west of the nucleus core, showing a strong
and broad peak. In addition, in the same direction [at position angle
(PA) ~-120°, i.e. close to the PA of the small-scale radio jet] at
1.7-2.5 arcsec, we also detected multiple narrow emission-line
components, with `greatly' enhanced [NII]/Halpha ratio (very similar
to the spectra of jets bow shocks). These results suggest that the BAL-I
system is generated in OF clouds associated with the parsec-scale jet.
The Hubble Space Telescope images show four (or possibly five) nuclear
superbubbles or shells with radii r~ 2.9, 1.5, 1.0, 0.6 and 0.2 kpc. For
these bubbles, the two-dimensional Halpha velocity field map and
two-dimensional spectra show the following. (i) At the border of the
more extended bubble (S1), a clear expansion of the shell with
blueshifted velocities (with circular shape and at a radius r~ 5.0
arcsec). This bubble shows a rupture arc - to the south - suggesting
that the bubble is in the blowout phase. The axis of this rupture or
ejection (at PA ~ 00°) is coincident with the axis of the
intermediate and large-scale structures detected at radio wavelengths.
(ii) In addition, in the three more external bubbles (S1, S2, S3), the
two-dimensional William Herschel Telescope spectra show multiple
emission-line components with OF velocities, of
OFBubble> S1, S2 and S3 =[-(650 - 420) +/- 30], [-500
+/- 30] and [-230 +/- 30] km s-1. (iii) In the whole
circumnuclear region (1.8 < r < 5 arcsec), the [NII]/Halpha and
[SII]/Halpha narrow emission-line ratios show high values (>0.8),
which are consistent with low-ionization nuclear emission-line region/OF
processes associated with fast velocity shocks. Therefore, we suggest
that these giant bubbles are associated with the large-scale nuclear OF
component, which is generated - at least in part - by the extreme
nuclear starburst: giant supernova/hypernova explosions.
The variability of the short-lived BAL-III NaI D system was studied,
covering almost all the period in which this system appeared (between
~1984 and 2004). We have found that the BAL-III light curve is clearly
asymmetric with a steep increase, a clear maximum and an exponential
fall (similar to the shape of a supernova light curve). The origin of
this BAL-III system is discussed, mainly in the framework of an extreme
explosive event, probably associated with giant supernova/hypernova
explosions.
Finally, the IR colour diagram and the ultraviolet BAL systems of IR +
GW/OF + FeII QSOs are analysed. This study shows two new BAL IR QSOs and
suggests/confirms that these objects could be nearby young BAL QSOs,
similar to those detected recently at z~ 6.0. We propose that the phase
of young QSOs is associated with accretion of a large amount of gas (by
the supermassive black hole) + extreme starbursts + extreme composite
OFs/BALs.
ER -
TY - Journal
T1 - A slow coronal mass ejection with rising X-ray source
A1 - Goff, C. P.
A1 - van Driel-Gesztelyi, L.
A1 - Harra, L. K.
A1 - Matthews, S. A.
A1 - Mandrini, C. H.
JO - Astronomy and Astrophysics
VL - 434
Y1 - 2005/5/1
SP - 761
EP - 771
KW - Sun: X-ray: gamma rays/ Sun: flares/ Sun: magnetic fields/ Sun: coronal mass ejections (CMEs)/ Sun: corona/ Sun: atmosphere
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...434..761G&db_key=AST&high=42a068d47519878
N2 - An eruptive event, which occurred on 16th April 2002, is discussed.
Using images from the Transition Region and Coronal Explorer (TRACE) at
195 Å, we observe a lifting flux rope which gives rise to a slow
coronal mass ejection (CME). There are supporting velocity observations
from the Coronal Diagnostic Spectrometer (CDS) on the Solar and
Heliospheric Observatory (SOHO), which illustrate the helical nature of
the structure. Additionally a rising coronal hard X-ray source, which is
observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI), is shown to follow the flux rope with a speed of ~60 km
s-1. It is also sampled by the CDS slit, although it has no
signature in the Fe XIX band. Following the passage of this source,
there is evidence from the CDS for down-flowing (cooling) material along
newly reconnected loops through Doppler velocity observations, combined
with magnetic field modeling. Later, a slow CME is observed with the
Large Angle and Spectroscopic Coronagraph (LASCO). We combine a
height-time profile of the flux rope at lower altitudes with the slow
CME. The rising flux rope speeds up by a factor of 1.7 at the start of
the impulsive energy release and goes through further acceleration
before reaching 1.5 solar radii. These observations support classical
CME scenarios in which the eruption of a filament precedes flaring
activity. Cusped flare loops are observed following the erupting flux
rope and their altitude increases with time. In addition we find RHESSI
sources both below and above the probable location of the reconnection
region.
ER -
TY - Journal
T1 - Interplanetary flux rope ejected from an X-ray bright point. The smallest magnetic cloud source-region ever observed
A1 - Mandrini, C. H.
A1 - Pohjolainen, S.
A1 - Dasso, S.
A1 - Green, L. M.
A1 - Démoulin, P.
A1 - van Driel-Gesztelyi, L.
A1 - Copperwheat, C.
A1 - Foley, C.
JO - Astronomy and Astrophysics
VL - 434
Y1 - 2005/5/1
SP - 725
EP - 740
KW - Sun: magnetic fields/ Sun: corona
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...434..725M&db_key=AST&high=42a068d47519878
N2 - Using multi-instrument and multi-wavelength observations (SOHO/MDI and
EIT, TRACE and Yohkoh/SXT), as well as computing the coronal magnetic
field of a tiny bipole combined with modelling of Wind in situ data, we
provide evidences for the smallest event ever observed which links a
sigmoid eruption to an interplanetary magnetic cloud (MC). The tiny
bipole, which was observed very close to the solar disc centre, had a
factor one hundred less flux than a classical active region (AR). In the
corona it had a sigmoidal structure, observed mainly in EUV, and we
found a very high level of non-potentiality in the modelled magnetic
field, 10 times higher than we have ever found in any AR. From May 11,
1998, and until its disappearance, the sigmoid underwent three intense
impulsive events. The largest of these events had extended EUV dimmings
and a cusp. The Wind spacecraft detected 4.5 days later one of the
smallest MC ever identified (about a factor one hundred times less
magnetic flux in the axial component than that of an average MC). The
link between this last eruption and the interplanetary magnetic cloud is
supported by several pieces of evidence: good timing, same coronal loop
and MC orientation, same magnetic field direction and magnetic helicity
sign in the coronal loops and in the MC. We further quantify this link
by estimating the magnetic flux (measured in the dimming regions and in
the MC) and the magnetic helicity (pre- to post-event change in the
solar corona and helicity content of the MC). Within the uncertainties,
both magnetic fluxes and helicities are in reasonable agreement, which
brings further evidences of their link. These observations show that the
ejections of tiny magnetic flux ropes are indeed possible and put new
constraints on CME models.
ER -
TY - Journal
T1 - Diagnostics of Quasar Broad Absorption Line Geometry: X-Ray Observations and Two-dimensional Optical Spectroscopy
A1 - Punsly, Brian
A1 - Lipari, Sebastian
JO - Astrophysical Journal
VL - 623
Y1 - 2005/4/1
SP - L101
EP - L104
KW - Accretion/ Accretion Disks/ Black Hole Physics/ Galaxies: Active/ Galaxies: Quasars: Absorption Lines/ X-Rays: Galaxies
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...623L.101P&db_key=AST&high=42a068d47519878
N2 - A new generation of sensitive X-ray measurements are indicating that the
existence of X-ray attenuation column densities,
NH>1024 cm-2, is quite common among
broad absorption line quasars (BALQSOs). This is significant to the
geometry of the broad absorption line (BAL) outflow. In particular, such
an X-ray shield also shields equatorial accretion disk winds from the
UV, thereby preventing high-velocity equatorial outflows from being
launched. By contrast, bipolar winds initiated by continuum radiation
pressure from the funnel of a slim accretion disk flare outward (like a
trumpet) and offer vastly different absorbing columns to the X-ray and
UV emission that are emitted from distinct regions of the disk, ~6M and
~10M-40M, respectively (where M is the radius of the black hole). Recent
numerical work indicates that it is also possible to launch bipolar
outflows from the inner regions of a thin disk. The recent discovery
with VLBI that the Galactic analog of a BALQSO, the X-ray binary
Circinus X-1 (with high-velocity P Cygni X-ray absorption lines), is
viewed virtually along the radio jet axis (and therefore along the spin
axis of the black hole and the normal to the accretion disk) has
rekindled interest in the bipolar models of BALQSOs. We explore this
possibility by studying the nearest BALQSO, Mrk 231. High-resolution
two-dimensional optical spectroscopy and VLBI mappings of the radio jet
axis indicate that the BAL outflow is parallel to the parsec-scale radio
jet.
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=42a068d47519878
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 - Observational Consequences of a Magnetic Flux Rope Emerging into the Corona
A1 - Gibson, S. E.
A1 - Fan, Y.
A1 - Mandrini, C.
A1 - Fisher, G.
A1 - Demoulin, P.
JO - Astrophysical Journal
VL - 617
Y1 - 2004/12/1
SP - 600
EP - 613
KW - Magnetohydrodynamics: MHD/ Sun: Corona/ Sun: Coronal Mass Ejections (CMEs)/ Sun: Magnetic Fields
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...617..600G&db_key=AST&high=42a068d47519878
N2 - We show that a numerical simulation of a magnetic flux rope emerging
into a coronal magnetic field predicts solar structures and dynamics
consistent with observations. We first consider the structure,
evolution, and relative location and orientation of S-shaped,
or sigmoid, active regions and filaments. The basic assumptions are that
(1) X-ray sigmoids appear at the regions of the flux rope known as
``bald-patch-associated separatrix surfaces (BPSSs), where, under
dynamic forcing, current sheets can form, leading to reconnection and
localized heating, and that (2) filaments are regions of enhanced
density contained within dips in the magnetic flux rope. We demonstrate
that the shapes and relative orientations and locations of the BPSS and
dipped field are consistent with observations of X-ray sigmoids and
their associated filaments. Moreover, we show that current layers indeed
form along the sigmoidal BPSS as the flux rope is driven by the kink
instability. Finally, we consider how apparent horizontal motions of
magnetic elements at the photosphere caused by the emerging flux rope
might be interpreted. In particular, we show that local correlation
tracking analysis of a time series of magnetograms for our simulation
leads to an underestimate of the amount of magnetic helicity transported
into the corona by the flux rope, largely because of undetectable
twisting motions along the magnetic flux surfaces. Observations of
rotating sunspots may provide better information about such rotational
motions, and we show that if we consider the separated flux rope legs as
proxies for fully formed sunspots, the amount of rotation that would be
observed before the region becomes kink unstable would be in the range
40°-200° per leg/sunspot, consistent with observations.
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=42a068d47519878
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 - What causes solar active region loops to exist at transition region temperatures?
A1 - Harra, Louise K.
A1 - Mandrini, Cristine H.
A1 - Matthews, Sarah A.
JO - Solar Physics
VL - 223
Y1 - 2004/9/1
SP - 57
EP - 76
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004SoPh..223...57H&db_key=AST&high=42a068d47519878
N2 - High-lying, dynamic loops have been observed at transition region
temperatures since Skylab observations. The nature of these loops has
been debated for many years with several explanations having been put
forward. These include that the loops are merely cooling from hotter
coronal loops, that they are produced from siphon flows, or that they
are loops heated only to transition region temperatures. In this paper
we will make use of combined SOHO-MDI (Michelson-Doppler Imager),
SOHO-CDS (Coronal Diagnostic Spectrometer) and Yohkoh SXT (Soft X-ray
Telescope) datasets in order to determine whether the appearance of
transition region loops is related to small-scale flaring in the corona,
and to estimate the magnetic configuration of the loops. The latter
allows us to determine the direction of plasma flows in the transition
region loops. We find that the appearance of the transition region loops
is often related to small-scale flaring in the corona and in this case
the transition region loops appear to be cooling with material draining
down from the loop top.
ER -
TY - Journal
T1 - Magnetic Helicity Budget of Solar-Active Regions from the Photosphere to Magnetic Clouds
A1 - Mandrini, C. H.
A1 - Démoulin, P.
A1 - van Driel-Gesztelyi, L.
A1 - López Fuentes, M. C.
JO - Astrophysics and Space Science
VL - 290
Y1 - 2004/4/1
SP - 319
EP - 344
KW - Sun: corona/ magnetic field/ coronal mass ejections (CMEs)
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..319M&db_key=AST&high=42a068d47519878
N2 - We have analyzed the long-term evolution of two active regions (ARs)
from their emergence through their decay using observations from several
instruments on board SoHO (MDI, EIT and LASCO) and Yohkoh/SXT. We have
computed the evolution of the relative coronal magnetic helicity
combining data from MDI and SXT with a linear force-free model of the
coronal magnetic field. Next, we have computed the injection of helicity
by surface differential rotation using MDI magnetic maps. To estimate
the depletion of helicity we have counted all the CMEs of which these
ARs have been the source, and we have evaluated their magnetic helicity
assuming a one to one correspondence with magnetic clouds with an
average helicity contain. When these three values (variation of coronal
magnetic helicity, injection by differential rotation and ejection via
CMEs) are compared, we find that surface differential rotation is a
minor contributor to the helicity budget since CMEs carry away at least
10 times more helicity than the one differential rotation can provide.
Therefore, the magnetic helicity flux needed in the global balance
should come from localized photospheric motions that, at least
partially, reflect the emergence of twisted flux tubes. We estimate that
the total helicity carried away in CMEs can be provided by the
end-to-end helicity of the flux tubes forming these ARs. Therefore, we
conclude that most of the helicity ejected in CMEs is generated below
the photosphere and emerges with the magnetic flux.
ER -
TY - Journal
T1 - Study of bi-orthogonal modes in magnetic butterflies
A1 - Mininni, Pablo D.
A1 - López Fuentes, Marcelo
A1 - Mandrini, Cristina H.
A1 - Gómez, Daniel O.
JO - Solar Physics
VL - 219
Y1 - 2004/2/1
SP - 367
EP - 378
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004SoPh..219..367M&db_key=AST&high=42a068d47519878
N2 - We present a bi-orthogonal decomposition of the temporal and latitudinal
distribution of solar magnetic fields from synoptic magnetograms.
Results are compared with a similar decomposition of the distribution of
sunspots since 1874. We show that the butterfly diagrams can be
interpreted as the result of approximately constant amplitudes and
phases of two oscillations with periods close to 22 years. A clear
periodicity of 7 years can also be identified in the most energetic
modes of both spatio-temporal series. These results can be used to
obtain relevant information concerning the physics of the solar dynamo.
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=42a068d47519878
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 - 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=42a068d47519878
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 - How are Emerging Flux, Flares and CMEs Related to Magnetic Polarity Imbalance in Midi Data?
A1 - Green, L. M.
A1 - Démoulin, P.
A1 - Mandrini, C. H.
A1 - Van Driel-Gesztelyi, L.
JO - Solar Physics
VL - 215
Y1 - 2003/8/1
SP - 307
EP - 325
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003SoPh..215..307G&db_key=AST&high=42a068d47519878
N2 - In order to understand whether major flares or coronal mass ejections
(CMEs) can be related to changes in the longitudinal photospheric
magnetic field, we study 4 young active regions during seven days of
their disk passage. This time period precludes any biases which may be
introduced in studies that look at the field evolution during the
short-term flare or CME period only. Data from the Michelson Doppler
Imager (MDI) with a time cadence of 96 min are used. Corrections are
made to the data to account for area foreshortening and angle between
line of sight and field direction, and also the underestimation of the
flux densities. We make a systematic study of the evolution of the
longitudinal magnetic field, and analyze flare and CME occurrence in the
magnetic evolution. We find that the majority of CMEs and flares occur
during or after new flux emergence. The flux in all four active regions
is observed to have deviations from polarity balance both on the long
term (solar rotation) and on the short term (few hours). The long-term
imbalance is not due to linkage outside the active region; it is
primarily related to the east-west distance from central meridian, with
the sign of polarity closer to the limb dominating. The sequence of
short-term imbalances are not closely linked to CMEs and flares and no
permanent imbalance remains after them. We propose that both kinds of
imbalance are due to the presence of a horizontal field component
(parallel to the photospheric surface) in the emerging flux.
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=42a068d47519878
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 - The Long-Term Evolution of AR 7978: Testing Coronal Heating Models
A1 - Démoulin, P.
A1 - van Driel-Gesztelyi, L.
A1 - Mandrini, C. H.
A1 - Klimchuk, J. A.
A1 - Harra, L.
JO - Astrophysical Journal
VL - 586
Y1 - 2003/3/1
SP - 592
EP - 605
KW - Magnetic Fields/ Sun: Corona/ Sun: Magnetic Fields/ Sun: X-Rays/ Gamma Rays
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...586..592D&db_key=AST&high=42a068d47519878
N2 - We derive the dependence of the mean coronal heating rate on the
magnetic flux density. Our results are based on a previous study of the
plasma parameters and the magnetic flux density (B) in the active region
NOAA 7978 from its birth to its decay, throughout five solar rotations
using the Solar and Heliospheric Observatory Michelson Doppler Imager,
Yohkoh Soft X-Ray Telescope (SXT), and Yohkoh Bragg Crystal Spectrometer
(BCS). We use the scaling laws of coronal loops in thermal equilibrium
to derive four observational estimates of the scaling of the coronal
heating with B (two from SXT and two from BCS observations). These
results are used to test the validity of coronal heating models. We find
that models based on the dissipation of stressed, current-carrying
magnetic fields are in better agreement with the observations than
models that attribute coronal heating to the dissipation of MHD waves
injected at the base of the corona. This confirms, with smaller error
bars, previous results obtained for individual coronal loops, as well as
for the global coronal emission of the Sun and cool stars. Taking into
account that the photospheric field is concentrated in thin magnetic
flux tubes, both SXT and BCS data are in best agreement with models
invoking a stochastic buildup of energy, current layers, and MHD
turbulence.
ER -
TY - Journal
T1 - The Long-Term Evolution of AR 7978: The Scalings of the Coronal Plasma Parameters with the Mean Photospheric Magnetic Field
A1 - van Driel-Gesztelyi, L.
A1 - Démoulin, P.
A1 - Mandrini, C. H.
A1 - Harra, L.
A1 - Klimchuk, J. A.
JO - Astrophysical Journal
VL - 586
Y1 - 2003/3/1
SP - 579
EP - 591
KW - Sun: Corona/ Sun: Magnetic Fields/ Sun: X-Rays/ Gamma Rays
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...586..579V&db_key=AST&high=42a068d47519878
N2 - We analyze the evolution of the fluxes observed in X-rays and correlate
them with the magnetic flux density in active region (AR) NOAA 7978 from
its birth throughout its decay, for five solar rotations. We use Solar
and Heliospheric Observatory Michelson Doppler Imager (MDI) data,
together with Yohkoh Soft X-Ray Telescope (SXT) and Yohkoh Bragg Crystal
Spectrometer (BCS) data, to determine the global evolution of the
temperature and the emission measure of the coronal plasma at times when
no significant brightenings were observed. We show that the mean X-ray
flux and derived parameters, temperature and emission measure (together
with other quantities deduced from them, such as the density and the
pressure), of the plasma in the AR follow power-law relationships with
the mean magnetic flux density (B). The exponents (b) of these power-law
functions (aBb) are derived using two different statistical
methods, a classical least-squares method in log-log plots and a
nonparametric method, which takes into account the fact that errors in
the data may not be normally distributed. Both methods give similar
exponents, within error bars, for the mean temperature and for both
instruments (SXT and BCS); in particular, b stays in the range [0.27,
0.31] and [0.24, 0.57] for full-resolution SXT images and BCS data,
respectively. For the emission measure, the exponent b lies in the range
[0.85, 1.35] and [0.45, 1.96] for SXT and BCS, respectively. The
determination of such power-law relations, when combined with the
results from coronal heating models, can provide us with powerful tools
for determining the mechanism responsible for the existence of the
high-temperature corona.
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=42a068d47519878
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 - Active region helicity evolution and related coronal mass ejection activity
A1 - Green, L. M.
A1 - López Fuentes, M. C.
A1 - Mandrini, C. H.
A1 - van Driel-Gesztelyi, L.
A1 - Démoulin, P.
JO - Advances in Space Research
VL - 32
Y1 - 2003/1/1
SP - 1959
EP - 1964
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AdSpR..32.1959G&db_key=AST&high=42a068d47519878
N2 - The computation of magnetic helicity has become increasingly important
in the studies of solar activity. Observations of helical structures in
the solar atmosphere, and their subsequent ejection into the
interplanetary medium, have resulted in considerable interest to find
the link between the amount of helicity in the coronal magnetic field
and the origin of coronal mass ejections (CMEs), which provide a natural
method to remove helicity from the corona. Recent works have endeavored
to find the source of helicity to explain the observed CME activity in
specific cases. The main candidates being differential rotation, shear
motions or a transfer of helicity from below the photosphere into the
corona. We study an active region for several rotations during 1997 and
1998 to investigate the relative importance of these mechanisms. We find
that photospheric differential rotation cannot provide the required
magnetic helicity to the corona and the ejected CMEs. Localized
photospheric motions can provide a larger helicity flux, though still
not sufficient.
ER -
TY - Journal
T1 - Observations of magnetic helicity
A1 - van Driel-Gesztelyi, L.
A1 - Démoulin, P.
A1 - Mandrini, C. H.
JO - Advances in Space Research
VL - 32
Y1 - 2003/1/1
SP - 1855
EP - 1866
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AdSpR..32.1855V&db_key=AST&high=42a068d47519878
N2 - The first observational signature of magnetic helicity in the solar
atmosphere (sunspot whirls) was discovered 77 years ago. Since then, the
existence of a cycle-invariant hemispheric helicity pattern has been
firmly established through current helicity and morphological studies.
During the last years, attempts were made to estimate/ measure magnetic
helicity from solar and interplanetary observations. Magnetic helicity
(unlike current helicity) is one of the few global quantities that is
conserved even in resistive magnetohydrodynamics (MHD) on a timescale
less than the global diffusion timescale, thus magnetic helicity studies
make it possible to trace helicity as it emerges from the
sub-photospheric layers to the corona and then is ejected via coronal
mass ejections (CMEs) into the interplanetary space reaching the Earth
in a magnetic cloud. We give an overview of observational studies on the
relative importance of different sources of magnetic helicity, i.e.
whether photospheric plasma motions (photospheric differential rotation
and localized shearing motions) or the twist of the emerging flux tubes
created under the photosphere (presumably by the radial shear in the
differential rotation in the tachocline) is the dominant helicity
source. We examine the sources of errors present in these early results
and try to judge how realistic they are.
ER -
TY - Journal
T1 - MWC 930 - a new luminous blue variable candidate
A1 - Miroshnichenko, A. S.
A1 - Bjorkman, K. S.
A1 - Grosso, M.
A1 - Levato, H.
A1 - Grankin, K. N.
A1 - Rudy, R. J.
A1 - Lynch, D. K.
A1 - Mazuk, S.
A1 - Puetter, R. C.
JO - Monthly Notices of the Royal Astronomical Society
VL - 364
Y1 - 2005/11/1
SP - 335
EP - 343
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.364..335M&db_key=AST&high=42a068d47522051
N2 - We present the results of optical high-resolution and near-infrared
low-resolution spectroscopy and multicolour optical and near-infrared
photometry of the emission-line star MWC 930. The spectrum is rich with
FeII emissions, most of which have P Cyg-type profiles. The emission
lines are strong and narrow, indicating a powerful stellar wind with a
low terminal velocity (v&infy;~ 140kms-1). The
photospheric absorption lines are broad and show splitting, which might
be due to the object's binarity. MWC 930 is most probably located in the
Norma spiral arm at a distance of D= 3-4kpc. This strong and slow wind
as well as the star's luminosity (logL/Lsolar~ 5.5) and the
infrared excess shape suggest that MWC 930 is an unusual B-type
supergiant, most likely undergoing the luminous blue variable
evolutionary phase.
ER -
TY - Journal
T1 - Elemental Abundance Studies of CP Stars. The Silicon Stars HD 87240 and HD 96729
A1 - Saffe, C.
A1 - Levato, H.
A1 - López-García, Z.
JO - Revista Mexicana de Astronomia y Astrofisica
VL - 41
Y1 - 2005/10/1
SP - 415
EP - 421
KW - Stars: chemically peculiar/ Stars: individual: HD 87240/ Stars: individual: HD 96729
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005RMxAA..41..415S&db_key=AST&high=42a068d47522051
N2 - We compared elemental abundances of field and open cluster Ap Si stars.
In particular, an analysis of the Ap Si stars HD 87240 and HD 96729 is
presented using an ATLAS9 model atmosphere and observational material
taken with a REOSC echelle spectrograph attached to the Jorge Sahade
2.15 m telescope at CASLEO. These chemically peculiar (CP) stars belong
to the southern hemisphere open clusters NGC 3114 and NGC 3532,
respectively. For HD 87240 and HD 96729, C is mostly solar, Mg and S are
slightly underabundant, Si and Ca are overabundant by factors between
1--10. Heavier elements are all overabundant, TiCrFe by factors of ~
10, SrYZr by factors between 100--1000 and rare earths by factors of
~ 1000 or more.
ER -
TY - Journal
T1 - Properties of galactic B[e] supergiants. IV. Hen 3-298 and Hen 3-303
A1 - Miroshnichenko, A. S.
A1 - Bjorkman, K. S.
A1 - Grosso, M.
A1 - Hinkle, K.
A1 - Levato, H.
A1 - Marang, F.
JO - Astronomy and Astrophysics
VL - 436
Y1 - 2005/6/1
SP - 653
EP - 659
KW - stars: emission-line/ B[e]/ stars: individual: Hen 3-298/ stars: Hen 3-303/ techniques: spectroscopic/ techniques: photometric/ circumstellar matter
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...436..653M&db_key=AST&high=42a068d47522051
N2 - We present the results of optical and near-IR spectroscopic and near-IR
photometric observations of the emission-line stars Hen 3-298 and Hen
3-303. Strong emission in the Halpha line is found in both objects.
The presence of Fe ii and [O i] emission lines in the spectrum of Hen
3-298 indicates that it is a B[e] star. The double-peaked CO line
profiles, found in the infrared spectrum of Hen 3-298, along with the
optical line profiles suggest that the star is surrounded by a rotating
circumstellar disc. Both objects also show infrared excesses, similar to
those of B[e] stars. The radial velocities of the absorption and
emission lines as well as a high reddening level suggest that the
objects are located in the Norma spiral arm at a distance of 3-4.5 kpc.
We estimated a luminosity of log L/L⊙ ~ 5.1 and a
spectral type of no earlier than B3 for Hen 3-298. Hen 3-303 seems to be
a less luminous B-type object (log L/L⊙ ~ 4.3),
located in the same spiral arm.
ER -
TY - Journal
T1 - Diffuse Component Spectra of Solar Active Regions at Submillimeter Wavelengths
A1 - Silva, Adriana V. R.
A1 - Laganá, Tatiana F.
A1 - Castro, C. Guillermo Gimenez
A1 - Kaufmann, Pierre
A1 - Costa, Joaquim E. R.
A1 - Levato, Hugo
A1 - Rovira, Marta
JO - Solar Physics
VL - 227
Y1 - 2005/4/1
SP - 265
EP - 281
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005SoPh..227..265S&db_key=AST&high=42a068d47522051
N2 - Solar maps at 212 and 405 GHz obtained by the Solar Submillimetric
Telescope (SST) show regions of enhanced brightness temperature, which
coincide with the location of active regions. A statistical study of the
radio emission from these active regions was performed for the first
time at such high frequencies during 23 days on June and July 2002, when
the atmospheric opacity was low. The brightest regions on the maps were
chosen for this study, where the brightness excess observed varies from
3 to 20% above quiet Sun levels (i.e., 200 1000 K) at both wavelengths.
Sizes of the regions of enhanced emission calculated at half the maximum
value were estimated to be between 2' and 7'. These sizes
agree with observed sizes of active regions at other wavelengths such as
Halpha and ultraviolet. An important result is that the flux density
spectra of all sources increase toward submillimeter frequencies,
yielding flux density spectral index with an average value of 2.0. The
flux density of the active region sources were complemented with that
from maps at 17 and 34 GHz from the Nobeyama Radio Heliograph. The
resulting spectra at all four frequencies were fit considering the flux
density to be due to thermal bremsstrahlung from the active region. In
the calculations, the source radius was assumed to be the mean of the
measured values at 212 and 405 K. The effective temperatures of the
radio emitting source, assumed homogeneous, obtained from this fit were
0.6 2.9 × 104 K, for source diameters of 2'
7'.
ER -
TY - Journal
T1 - Line Identification of the Si Star HD 87240
A1 - Saffe, C.
A1 - Levato, H.
A1 - López-García, Z.
JO - Revista Mexicana de Astronomia y Astrofisica
VL - 40
Y1 - 2004/10/1
SP - 231
EP - 242
KW - Stars: chemically peculiar - Stars: individual: HD 87240
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004RMxAA..40..231S&db_key=AST&high=42a068d47522051
N2 - Line identifications are presented for the peculiar Apstar HD7240
(delta = - 59° 51' 00.1'') in the spectral region lambdalambda
3710-5520. This object is a member of the southern open cluster NGC114.
Comparison of this object with other field silicon stars shows that it
shares many of their line anomalies.
ER -
TY - Journal
T1 - SB9: The ninth catalogue of spectroscopic binary orbits
A1 - Pourbaix, D.
A1 - Tokovinin, A. A.
A1 - Batten, A. H.
A1 - Fekel, F. C.
A1 - Hartkopf, W. I.
A1 - Levato, H.
A1 - Morrell, N. I.
A1 - Torres, G.
A1 - Udry, S.
JO - Astronomy and Astrophysics
VL - 424
Y1 - 2004/9/1
SP - 727
EP - 732
KW - stars: binaries: spectroscopic/ astronomical data bases: miscellaneous/ catalogs
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...424..727P&db_key=AST&high=42a068d47522051
N2 - The Ninth Catalogue of Spectroscopic Binary Orbits
(http://sb9.astro.ulb.ac.be) continues the series of compilations of
spectroscopic orbits carried out over the past 35 years by Batten and
collaborators. As of 2004 May 1st, the new Catalogue holds orbits for
2386 systems. Some essential differences between this catalogue and its
predecessors are outlined and three straightforward applications are
presented: (1) completeness assessment: period distribution of SB1s and
SB2s; (2) shortest periods across the H-R diagram; (3)
period-eccentricity relation.
ER -
TY - Journal
T1 - Abundance determinations with Blackwell diagrams
A1 - Saffe, C.
A1 - Levato, H.
JO - Astronomy and Astrophysics
VL - 418
Y1 - 2004/5/1
SP - 1083
EP - 1087
KW - stars: abundances/ stars: chemically peculiar
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...418.1083S&db_key=AST&high=42a068d47522051
N2 - We have performed an elemental abundance analysis for Sirius, Vega, and
three peculiar silicon stars: HD 43819, HD 192913 and HD 133029 using
Blackwell diagrams and observational data taken from the literature. We
have compared our results with previous abundance and microturbulence
velocity determinations to check the validity of Blackwell diagrams
applied to CP stars. We found a very good agreement.
ER -
TY - Journal
T1 - Properties of galactic B[e] supergiants. III. MWC 300
A1 - Miroshnichenko, A. S.
A1 - Levato, H.
A1 - Bjorkman, K. S.
A1 - Grosso, M.
A1 - Manset, N.
A1 - Men'shchikov, A. B.
A1 - Rudy, R. J.
A1 - Lynch, D. K.
A1 - Mazuk, S.
A1 - Venturini, C. C.
A1 - Puetter, R. C.
A1 - Perry, R. B.
JO - Astronomy and Astrophysics
VL - 417
Y1 - 2004/4/1
SP - 731
EP - 743
KW - stars: emission-line/ Be/ stars: individual: MWC 300/ techniques: spectroscopic/ circumstellar matter/ radiative transfer
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...417..731M&db_key=AST&high=42a068d47522051
N2 - We present the results of optical and near-IR spectroscopic and mid-IR
imaging observations of the emission-line star MWC 300. Its properties
and evolutionary state are still under debate (a B[e] supergiant or a
Herbig Be star). For the first time we detected radial velocity
variations of the photospheric lines and found a correlation between
them and those of the He I lambda5876 Åline. Most of the pure
emission lines had stable positions for nearly 20 years. New estimates
of the object's luminosity (log L/L⊙=5.1±0.1),
distance (D=1.8±0.2 kpc), and systemic velocity (+26±2 km
s-1) were derived. We found that both the circumstellar
extinction in the disk-like dusty envelope and the interstellar
extinction play a significant role in the attenuation of the stellar
brightness. Our 2D modeling of the observed spectral energy distribution
in the wavelength range from 0.3 mum to 1.3 mm suggests that the star
is viewed through a gaseous-and-dusty flared disk with an opening angle
of 30 °, an inclination angle of 10 °, an equatorial optical
depth tauV=3.0, and a total mass of 0.08
M⊙. We argue that MWC 300 is most likely a binary
system, because of the similarities of its observed parameters with
those of recognized B[e] binaries.
Partially based on observations collected at the Canada-France-Hawaii
telescope (CFHT), operated by the National Research Council of Canada,
the Centre National de la Recherche Scientifique, and Univeristy of
Hawaii.
ER -
TY - Journal
T1 - A New Solar Burst Spectral Component Emitting Only in the Terahertz Range
A1 - Kaufmann, Pierre
A1 - Raulin, Jean-Pierre
A1 - de Castro, C. G. Giménez
A1 - Levato, Hugo
A1 - Gary, Dale E.
A1 - Costa, Joaquim E. R.
A1 - Marun, Adolfo
A1 - Pereyra, Pablo
A1 - Silva, Adriana V. R.
A1 - Correia, Emilia
JO - Astrophysical Journal
VL - 603
Y1 - 2004/3/1
SP - L121
EP - L124
KW - Plasmas/ Radiation Mechanisms: Nonthermal/ Submillimeter/ Sun: Flares/ Sun: Infrared/ Sun: Radio Radiation
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...603L.121K&db_key=AST&high=42a068d47522051
N2 - Solar flare energy manifestations were believed to be the result of the
same kind of particle acceleration. It is generally accepted that a
population of relativistic electrons accelerated during the impulsive
phase of solar flares produces microwaves by synchrotron losses in the
solar magnetic field and X-rays by collisions in denser regions of the
solar atmosphere. We report the discovery of a new intense solar flare
spectral radiation component, peaking somewhere in the shorter
submillimeter to far-infrared range, identified during the 2003 November
4 large flare. The new solar submillimeter telescope, designed to extend
the frequency range to above 100 GHz, detected this new component with
increasing fluxes between 212 and 405 GHz. It appears along with, but is
separated from, the well-known gyrosynchrotron emission component seen
at microwave frequencies. The novel emission component had three major
peaks with time, originated in a compact source whose position remained
remarkably steady within 15". Intense subsecond pulses are superposed
with excess fluxes also increasing with frequency and amplitude
increasing with the pulse repetition rate. The origin of the terahertz
emission component during the flare impulsive phase is not known. It
might be representative of emission due to electrons with energies
considerably larger than the energies assumed to explain emission at
microwaves. This component can attain considerably larger intensities in
the far-infrared, with a spectrum extending to the white-light emission
observed for that flare.
ER -
TY - Journal
T1 - Spectroscopy of the growing circumstellar disk in the delta Scorpii Be binary
A1 - Miroshnichenko, A. S.
A1 - Bjorkman, K. S.
A1 - Morrison, N. D.
A1 - Wisniewski, J. P.
A1 - Manset, N.
A1 - Levato, H.
A1 - Grosso, M.
A1 - Pollmann, E.
A1 - Buil, C.
A1 - Knauth, D. C.
JO - Astronomy and Astrophysics
VL - 408
Y1 - 2003/9/1
SP - 305
EP - 311
KW - techniques: spectroscopic/ stars: circumstellar matter/ stars: individual: delta Scorpii/ stars: binaries: spectroscopic/ stars: Be stars
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...408..305M&db_key=AST&high=42a068d47522051
N2 - We present the results of a spectroscopic monitoring program of the
binary system delta Scorpii, whose primary became a Be star after the
last periastron encounter in the Summer of 2000. The observations cover
a period of 2 years (March 2001-June 2003) and are a continuation of our
previous campaign reported in Miroshnichenko et al. (\cite{metal}). We
found that the emission-line spectrum was gradually strengthening over
the whole monitoring period. Several short-term increases of the line
emission, possibly due to outbursts of matter ejected from the stellar
surface, were detected. The outbursts seem to be responsible for the
brightness fadings, seen afterwards. We attempt to explain the overall
observed line and continuum behaviour in terms of a circumstellar disk,
growing in density and size. The disk is most likely Keplerian with an
outer radius of ~10 Rstar and a mean expansion speed of ~
0.4 km s-1.
Tables 1-2 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/408/305}
ER -
TY - Journal
T1 - Properties of galactic B[e] supergiants II. HDE 327083
A1 - Miroshnichenko, A. S.
A1 - Levato, H.
A1 - Bjorkman, K. S.
A1 - Grosso, M.
JO - Astronomy and Astrophysics
VL - 406
Y1 - 2003/8/1
SP - 673
EP - 683
KW - stars: emission-line/ Be/ stars: individual: HDE 327083/ techniques: spectroscopic/ techniques: polarimetric
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...406..673M&db_key=AST&high=42a068d47522051
N2 - The emission-line object HDE 327083 has long been considered to be one
of the most luminous stars in the Milky Way. Nevertheless, no reliable
physical parameters have been published for it. Our high-resolution
optical spectroscopy revealed the presence of photospheric lines of a
cool luminous companion. We detected significant antiphased radial
velocity variations of the emission and absorption lines. The data
obtained are still insufficient to derive a reliable orbital solution;
however, the orbital period is most likely of the order of 6 months. We
conclude that HDE 327083 is a binary system consisting of an early
B-type primary and early F-type secondary, with luminosities log L/L
sun = 5.0+/- 0.4 and 4.2 +/- 0.4, respectively, and whose
orbital plane is viewed nearly edge-on. We also obtained new multicolour
optical and infrared photometry of HDE 327083. From both the photometric
and spectroscopic data, we found that the system is located at a
distance of 1.5 +/- 0.5 kpc. Most of the circumstellar gas seems to be
orbiting the primary and is distributed in a mildly flattened envelope
with a height scale and velocity decreasing outward from the star. We
suggest that HDE 327083 represents an advanced evolutionary stage of a
beta Lyrae type binary.
ER -
TY - Journal
T1 - Large changes in Pluto's atmosphere as revealed by recent stellar occultations
A1 - Sicardy, B.
A1 - Widemann, T.
A1 - Lellouch, E.
A1 - Veillet, C.
A1 - Cuillandre, J.-C.
A1 - Colas, F.
A1 - Roques, F.
A1 - Beisker, W.
A1 - Kretlow, M.
A1 - Lagrange, A.-M.
A1 - Gendron, E.
A1 - Lacombe, F.
A1 - Lecacheux, J.
A1 - Birnbaum, C.
A1 - Fienga, A.
A1 - Leyrat, C.
A1 - Maury, A.
A1 - Raynaud, E.
A1 - Renner, S.
A1 - Schultheis, M.
A1 - Brooks, K.
A1 - Delsanti, A.
A1 - Hainaut, O. R.
A1 - Gilmozzi, R.
A1 - Lidman, C.
A1 - Spyromilio, J.
A1 - Rapaport, M.
A1 - Rosenzweig, P.
A1 - Naranjo, O.
A1 - Porras, L.
A1 - Díaz, F.
A1 - Calderón, H.
A1 - Carrillo, S.
A1 - Carvajal, A.
A1 - Recalde, E.
A1 - Cavero, L. Gaviria
A1 - Montalvo, C.
A1 - Barría, D.
A1 - Campos, R.
A1 - Duffard, R.
A1 - Levato, H.
JO - Nature
VL - 424
Y1 - 2003/7/1
SP - 168
EP - 170
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Natur.424..168S&db_key=AST&high=42a068d47522051
N2 - Pluto's tenuous nitrogen atmosphere was first detected by the imprint
left on the light curve of a star that was occulted by the planet in
1985 (ref. 1), and studied more extensively during a second occultation
event in 1988 (refs 2-6). These events are, however, quite rare and
Pluto's atmosphere remains poorly understood, as in particular the
planet has not yet been visited by a spacecraft. Here we report data
from the first occultations by Pluto since 1988. We find that, during
the intervening 14 years, there seems to have been a doubling of the
atmospheric pressure, a probable seasonal effect on Pluto.
ER -
TY - Journal
T1 - Launch of solar coronal mass ejections and submillimeter pulse bursts
A1 - Kaufmann, Pierre
A1 - Giménez de Castro, C. Guillermo
A1 - Makhmutov, Vladimir S.
A1 - Raulin, Jean-Pierre
A1 - Schwenn, Rainer
A1 - Levato, H.
A1 - Rovira, M.
JO - Journal of Geophysical Research (Space Physics)
VL - 108g
Y1 - 2003/7/1
EP - 1
KW - Magnetospheric Physics: Forecasting/ Interplanetary Physics: Energetic particles/ solar/ Solar Physics/ Astrophysics/ and Astronomy: Coronal mass ejections/ Radio Science: Radio astronomy
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003JGRA.108g.SSH5K&db_key=AST&high=42a068d47522051
N2 - The rapid solar spikes (100-500 ms) recently discovered at submillimeter
waves bring new possibilities to investigate energetic processes near
the solar surface that might have an important role in the launch and
propelling of ionized mass away from the Sun. We present a study on the
association between the launch time of coronal mass ejections (CMEs)
observed by the LASCO instruments on the SOHO spacecraft and the onset
of the new kind of rapid solar spikes (100-500 ms) observed at
submillimetric waves (212 and 405 GHz) by the new Solar Submm-wave
Telescope (SST). We investigated six submm-wave events, all found
associated to CMEs. Seven related CME were identified. Five of them were
associated with flares with large GOES class soft X-rays, presenting
distinct time histories and associations at other energy ranges, and two
of them were related to flares behind the solar limb, with simultaneous
related activity observed in the visible solar disk. Ultraviolet images
from EIT on SOHO show some kind of small or large-scale magnetic
activity or brightening for all events. The extrapolation of apparent
CME positions to the solar surface show that they occurred nearly
coincident in time with the onset of submm-wave pulses for all six
events. These results suggest that pulse bursts might be representative
of an important early signature of CMEs, especially for events beginning
near the center of the solar disk, sometimes identified as ``halo''
CMEs. They lead to several challenging questions relative to the
physical nature of the pulses and its association to the launch and
acceleration of coronal mass ejections. Although these evidences may
favor multiple rapid energy releases at the origin near the solar
surface, they require further research in order to better understand
both diagnostics and model descriptions.
ER -
TY - Journal
T1 - Properties of Fast Submillimeter Time Structures during a Large Solar Flare
A1 - Raulin, Jean-Pierre
A1 - Kaufmann, Pierre
A1 - Giménez de Castro, Carlos G.
A1 - Pacini, Alessandra A.
A1 - Makhmutov, Vladimir S.
A1 - Levato, Hugo
A1 - Rovira, Marta
JO - Astrophysical Journal
VL - 592
Y1 - 2003/7/1
SP - 580
EP - 589
KW - Gamma Rays: Bursts/ Sun: Flares/ Sun: Radio Radiation
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...592..580R&db_key=AST&high=42a068d47522051
N2 - We report properties of fast varying submillimeter emission during one
of the strongest solar radio flares of solar cycle 23. Emission was
obtained by the Solar Submillimeter-Wave Telescope at 212 and 405 GHz
and compared with hard X-ray and gamma-ray counts up to few tens of
MeV photon energy ranges. We employ different methods to detect and
characterize flux density variations and find that during the impulsive
phase of the event, the closer in time to the peak flare, the higher the
occurrence of the fastest and brightest time structures. The good
comparison with hard X-ray and gamma-ray count rates indicates that
fast submillimeter pulses are the signatures of primary energetic
injections. The characteristics of the fast spikes at 212 and 405 GHz,
such as their flux density and localization, compared to those of the
underlying slower impulsive component, also suggest that their nature is
different.
ER -
TY - Journal
T1 - Spectroscopic Binaries in the Open Cluster Trumpler 16 Revisited
A1 - Luna, G. J.
A1 - Levato, H.
A1 - Malaroda, S.
A1 - Grosso, M.
JO - Informational Bulletin on Variable Stars
VL - 5375
Y1 - 2003/2/1
SP - 1
KW - spectroscopy
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003IBVS.5375....1L&db_key=AST&high=42a068d47522051
N2 - We have recalculated the orbits of 3 binary systems, members of the open
cluster Trumpler 16 in the Carina region. We have added new observations
to those available in the literature. We have improved considerably the
precision of some of the orbital parameters. We could not find
significant radial velocity variations for two suspected binary systems
in the same cluster.
ER -
TY - Journal
T1 - GRB 050904 at redshift 6.3: observations of the oldest cosmic explosion after the Big Bang
A1 - Tagliaferri, G.
A1 - Antonelli, L. A.
A1 - Chincarini, G.
A1 - Fernández-Soto, A.
A1 - Malesani, D.
A1 - della Valle, M.
A1 - D'Avanzo, P.
A1 - Grazian, A.
A1 - Testa, V.
A1 - Campana, S.
A1 - Covino, S.
A1 - Fiore, F.
A1 - Stella, L.
A1 - Castro-Tirado, A. J.
A1 - Gorosabel, J.
A1 - Burrows, D. N.
A1 - Capalbi, M.
A1 - Cusumano, G.
A1 - Conciatore, M. L.
A1 - D'Elia, V.
A1 - Filliatre, P.
A1 - Fugazza, D.
A1 - Gehrels, N.
A1 - Goldoni, P.
A1 - Guetta, D.
A1 - Guziy, S.
A1 - Held, E. V.
A1 - Hurley, K.
A1 - Israel, G. L.
A1 - Jelínek, M.
A1 - Lazzati, D.
A1 - López-Echarri, A.
A1 - Melandri, A.
A1 - Mirabel, I. F.
A1 - Moles, M.
A1 - Moretti, A.
A1 - Mason, K. O.
A1 - Nousek, J.
A1 - Osborne, J.
A1 - Pellizza, L. J.
A1 - Perna, R.
A1 - Piranomonte, S.
A1 - Piro, L.
A1 - de Ugarte Postigo, A.
A1 - Romano, P.
JO - Astronomy and Astrophysics
VL - 443
Y1 - 2005/11/1
SP - L1
EP - L5
KW - cosmology: observations/ early Universe/ gamma rays: bursts/ gamma rays: individual: GRB 050904
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...443L...1T&db_key=AST&high=42a068d47526716
N2 - We present optical and near-infrared observations of the afterglow of
the gamma-ray burst GRB 050904. We derive a photometric redshift z =
6.3, estimated from the presence of the Lyman break falling between the
I and J filters. This is by far the most distant GRB known to date. Its
isotropic-equivalent energy is 3.4 × 1053 erg in the
rest-frame 110-1100 keV energy band. Despite the high redshift, both the
prompt and the afterglow emission are not peculiar with respect to other
GRBs. We find a break in the J-band light curve at tb = 2.6
± 1.0 d (observer frame). If we assume this is the jet break, we
derive a beaming-corrected energy E_gamma ~ (4 div 12) ×
1051 erg. This limit shows that GRB 050904 is consistent with
the Amati and Ghirlanda relations. This detection is consistent with the
expected number of GRBs at z > 6 and shows that GRBs are a powerful
tool to study the star formation history up to very high redshift.
ER -
TY - Journal
T1 - Chromospheric models of solar analogues with different activity levels
A1 - Vieytes, M.
A1 - Mauas, P.
A1 - Cincunegui, C.
JO - Astronomy and Astrophysics
VL - 441
Y1 - 2005/10/1
SP - 701
EP - 709
KW - radiative transfer/ stars: atmospheres/ stars: activity
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...441..701V&db_key=AST&high=42a068d47526716
N2 - We computed chromospheric models of the Sun as a star and of nine solar
analogues. The atmospheric models were constructed to obtain the best
possible match with the Ca II K and Hbeta lines, including the
asymmetry of the lines due to macroscopic velocity fields. The stars
were chosen with 0.62 < B-V< 0.68 (the solar B-V=0.65) and have a
wide variety of magnetic activity levels, which allows us to study the
differences in atmospheric structures induced by activity. For the less
active stars we found that the changes with activity are in the region
of the temperature minimum, while the most active stars show changes all
along their atmospheric structures, mainly in the upper chromosphere.
Regarding the macroscopic velocity fields, we can distinguish between
the two groups. The most active group has a velocity field in the
temperature-minimum region, and the other group in the chromospheric
plateau. We also computed the net radiative losses for each model, and
found that they depend linearly on the usual index of chromospheric
activity, SCa II.
ER -
TY - Journal
T1 - Further evidence for the presence of a neutron star in 4U 2206+54. INTEGRAL and VLA observations
A1 - Blay, P.
A1 - Ribó, M.
A1 - Negueruela, I.
A1 - Torrejón, J. M.
A1 - Reig, P.
A1 - Camero, A.
A1 - Mirabel, I. F.
A1 - Reglero, V.
JO - Astronomy and Astrophysics
VL - 438
Y1 - 2005/8/1
SP - 963
EP - 972
KW - stars: individual: 4U 2206+54/ X-rays: binaries/ radio continuum: stars/ accretion/ accretion disks/ magnetic fields/ stars: binaries: close
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...438..963B&db_key=AST&high=42a068d47526716
N2 - The majority of High Mass X-ray Binaries (HMXBs) behave like X-ray
pulsars, revealing that they contain a magnetised neutron star. Among
the four HMXBs showing neither pulsations nor the characteristics of
accreting black holes, there is the unusual HMXB 4U
2206+54. Here we present contemporaneous high-energy and radio
observations of this system conducted with INTEGRAL and the VLA, in
order to unveil its nature. The high-energy spectra show clear
indications of the presence of an absorption feature at ~32 keV. This is
the third high-energy observatory to reveal marginal evidence of this
feature, giving strong support to the existence of a cyclotron resonance
scattering feature, which implies a magnetic field of 3.6×
1012 G. On the other hand, the source is not detected at
centimetre radio wavelengths with a 3sigma upper limit of 0.039 mJy.
The expected radio emission for an accreting black hole in the low/hard
state, inferred from X-ray flux measurements, would be at least 60 times
greater than the measured upper limit. Both results firmly indicate
that, in spite of the absence of pulsations, 4U
2206+54 hosts a magnetic accreting neutron star, the first one
not to be observed as an X-ray pulsar.
ER -
TY - Journal
T1 - Structuring eccentric-narrow planetary rings
A1 - Papaloizou, J. C. B.
A1 - Melita, M. D.
JO - Icarus
VL - 175
Y1 - 2005/6/1
SP - 435
EP - 451
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..175..435P&db_key=AST&high=42a068d47526716
N2 - A simple and general description of the dynamics of a narrow-eccentric
ring is presented. We view an eccentric ring which precesses uniformly
at a slow rate as exhibiting a global m=1 mode, which can be seen as
originating from a standing wave superposed on an axisymmetric
background. We adopt a continuum description using the language of fluid
dynamics which gives equivalent results for the secular dynamics of thin
rings as the well-known description in terms of a set of discrete
elliptical streamlines formulated by Goldreich and Tremaine (1979,
Astron. J. 84, 1638 1641). We use this to discuss the nonlinear mode
interactions that appear in the ring through the excitation of higher m
modes because of the coupling of the m=1 mode with an external satellite
potential, showing that they that can lead to the excitation of the m=1
mode through a feedback process. In addition to the external
perturbations by neighboring satellites, our model includes effects due
to inelastic inter-particle collisions. Two main conditions for the ring
to be able to maintain a steady m=1 normal mode are obtained. One can be
expressed as an integral condition for the normal mode pattern to
precess uniformly, which requires the correct balance between the
differential precession induced by the oblateness of the central planet,
self-gravity and collisional effects is the continuum form of that
obtained from the N streamline model of Goldreich and Tremaine (1979,
Astron. J. 84, 1638 1641). The other condition, not before examined in
detail, is for the steady maintenance of the nonzero radial action that
the ring contains because of its finite normal mode. This requires a
balance between injection due to eccentric resonances arising from
external satellites and additional collisional damping associated with
the presence of the m=1 mode. We estimate that such a balance can occur
in the É›-ring of Uranus, given its currently observed physical
and orbital parameters.
ER -
TY - Journal
T1 - Characterizing a new class of variability in GRS 1915+105 with simultaneous INTEGRAL/RXTE observations
A1 - Hannikainen, D. C.
A1 - Rodriguez, J.
A1 - Vilhu, O.
A1 - Hjalmarsdotter, L.
A1 - Zdziarski, A. A.
A1 - Belloni, T.
A1 - Poutanen, J.
A1 - Wu, K.
A1 - Shaw, S. E.
A1 - Beckmann, V.
A1 - Hunstead, R. W.
A1 - Pooley, G. G.
A1 - Westergaard, N. J.
A1 - Mirabel, I. F.
A1 - Hakala, P.
A1 - Castro-Tirado, A.
A1 - Durouchoux, Ph.
JO - Astronomy and Astrophysics
VL - 435
Y1 - 2005/6/1
SP - 995
EP - 1004
KW - X-rays: binaries/ X-rays: stars/ X-rays: individual: GRS 1915+105/ gamma rays: observations/ black hole physics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...435..995H&db_key=AST&high=42a068d47526716
N2 - We report on the analysis of 100 ks INTEGRAL observations of the
Galactic microquasar GRS 1915+105. We focus on
INTEGRAL Revolution number 48 when the source was found to exhibit a new
type of variability as preliminarily reported in Hannikainen (2003,
A&A, 411, L415). The variability pattern, which we name xi, is
characterized by a pulsing behaviour, consisting of a main pulse and a
shorter, softer, and smaller amplitude precursor pulse, on a timescale
of 5 min in the JEM-X 3-35 keV lightcurve. We also present simultaneous
RXTE data. From a study of the individual RXTE/PCA pulse profiles we
find that the rising phase is shorter and harder than the declining
phase, which is opposite to what has been observed in other otherwise
similar variability classes in this source. The position in the
colour-colour diagram throughout the revolution corresponds to State A
(Belloni et al. 2000, A&A, 355, 271) but not to any previously known
variability class. We separated the INTEGRAL data into two subsets
covering the maxima and minima of the pulses and fitted the resulting
two broadband spectra with a hybrid thermal-non-thermal Comptonization
model. The fits show the source to be in a soft state characterized by a
strong disc component below ~6 keV and Comptonization by both thermal
and non-thermal electrons at higher energies.
ER -
TY - Journal
T1 - On the local birth place of Geminga
A1 - Pellizza, L. J.
A1 - Mignani, R. P.
A1 - Grenier, I. A.
A1 - Mirabel, I. F.
JO - Astronomy and Astrophysics
VL - 435
Y1 - 2005/5/1
SP - 625
EP - 630
KW - stars: neutron/ pulsars: general/ pulsars: individual: Geminga/ solar neighbourhood
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...435..625P&db_key=AST&high=42a068d47526716
N2 - Using estimates of the distance and proper motion of
Geminga and the constraints on its radial velocity
posed by the shape of its bow shock, we investigate its birth place by
tracing its space motion backwards in time. Our results exclude the
lambda Ori association as the origin site because
of the large distance between both objects at any time. Our simulations
place the birth region at approximately 90-240 pc from the Sun, between
197° and 199° in Galactic longitude and -16° and -8° in
latitude, most probably inside the Cas-Tau OB
association or the Ori OB1a association. We discard
the possibility of the progenitor being a massive field star. The
association of Geminga with either stellar
association implies an upper limit of M ≈ 15 M⊙ for
the mass of its progenitor. We also propose new members for the
Cas-Tau and Ori OB1 associations.
ER -
TY - Journal
T1 - INTEGRAL discovery of persistent hard X-ray emission from the Soft Gamma-ray Repeater SGR 1806-20
A1 - Mereghetti, S.
A1 - Götz, D.
A1 - Mirabel, I. F.
A1 - Hurley, K.
JO - Astronomy and Astrophysics
VL - 433
Y1 - 2005/4/1
SP - L9
EP - L12
KW - gamma rays: bursts/ pulsars: general/ stars: individual: SGR 1806-20
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...433L...9M&db_key=AST&high=42a068d47526716
N2 - We report the discovery of persistent hard X-ray emission extending up
to 150 keV from the soft gamma-ray repeater SGR 1806-20 using data
obtained with the INTEGRAL satellite in 2003-2004. Previous observations
of hard X-rays from objects of this class were limited to short duration
bursts and rare transient episodes of strongly enhanced luminosity
(``flares''). The emission observed with the IBIS instrument
above 20 keV has a power law spectrum with photon index in the range
1.5-1.9 and a flux of 3 milliCrabs, corresponding to a 20-100 keV
luminosity of ~1036 erg s-1 (for a distance of 15
kpc). The spectral hardness and the luminosity correlate with the level
of source activity as measured from the number of emitted bursts.
Based on observations with INTEGRAL, an ESA project with instruments and
science data centre funded by ESA member states (especially the PI
countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech
Republic and Poland, and with the participation of Russia and the USA.
ER -
TY - Journal
T1 - 1E 1740.7-2942: Temporal and spectral evolution from INTEGRAL and RXTE observations
A1 - del Santo, M.
A1 - Bazzano, A.
A1 - Zdziarski, A. A.
A1 - Smith, D. M.
A1 - Bezayiff, N.
A1 - Farinelli, R.
A1 - de Cesare, G.
A1 - Ubertini, P.
A1 - Bird, A. J.
A1 - Cadolle Bel, M.
A1 - Capitanio, F.
A1 - Goldwurm, A.
A1 - Malizia, A.
A1 - Mirabel, I. F.
A1 - Natalucci, L.
A1 - Winkler, C.
JO - Astronomy and Astrophysics
VL - 433
Y1 - 2005/4/1
SP - 613
EP - 617
KW - gamma rays: observations/ radiation mechanisms: non-thermal/ stars: individual:/ 1E 1740.7-2942/ X-rays: binaries/ black hole physics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...433..613D&db_key=AST&high=42a068d47526716
N2 - We present results of the monitoring of the black hole candidate 1E
1740.7-2942 with INTEGRAL, in combination with simultaneous observations
by RXTE. We concentrate on broad-band spectra from INTEGRAL/IBIS and
RXTE/PCA instruments. During our observations, the source spent most of
its time in the canonical low/hard state with the measured flux
variation within a factor of two. In 2003 September the flux started to
decline and in 2004 February it was below the sensitivity level of the
INTEGRAL and RXTE instruments. Notably, during the decline phase the
spectrum changed, becoming soft and typical of black-hole binaries in
the intermediate/soft state.
Based on observations with INTEGRAL, an ESA project with instruments and
science data centre funded by ESA member states (especially the PI
countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech
Republic and Poland, and with participation of Russia and the USA.
ER -
TY - Journal
T1 - Sculpting the outer Edgeworth-Kuiper belt: stellar encounter followed by planetary perturbations
A1 - Melita, M. D.
A1 - Larwood, J. D.
A1 - Williams, I. P.
JO - Icarus
VL - 173
Y1 - 2005/2/1
SP - 559
EP - 573
KW - origin/ comets/ Dynamics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..173..559M&db_key=AST&high=42a068d47526716
N2 - We consider a close stellar fly-by as an explanation for the abrupt
termination of the classical Edgeworth-Kuiper belt at around 50 AU from
the Sun, and also for the high values of orbital excitation observed. By
the use of numerical simulations we study a scenario in which a close
stellar fly-by truncates the trans-neptunian cometary population as a
result of strong gravitational perturbations. The results from some
representative cases are compared with the presently observed
distribution of EKBOs. Our findings suggest that---when
observational biases are taken into account---this scenario can
reproduce some features of the observed distribution. However, although
it is clear that fly-by models are able to generate high values of
eccentricity and orbital inclination in the outer particle distribution,
this comes at the expense of preserving any low eccentricity particle
orbits. The nearly vertical distribution of eccentricities over
semimajor axis found at around 48 AU in the EKB cannot be modeled by the
use of a stellar fly-by encounter alone. Hence we consider long
timescale planetary perturbations and collisional self-interactions that
act on the perturbed distribution after a fly-by encounter, and which
have the potential to provide a more complete description of the EKBO
distribution. However, even when these have been taken into account, the
transport of objects from `hot' to `cold' orbits may not be sufficient
to cover the range of semimajor axes that are observed in the later.
Thus, an alternative origin for the low inclination and eccentricity
orbits seems likely. The effect of such an encounter on the inner Oort
cloud is studied, and we conclude that comets in very large and
elongated orbits can be transported to the trans-neptunian region by
this mechanism.
ER -
TY - Journal
T1 - Resonantly Forced Eccentric Ringlets: Relationships Between Surface Density, Resonance Location, Eccentricity And Eccentricity-Gradient
A1 - Melita, M. D.
A1 - Papaloizou, J. C. B.
JO - Celestial Mechanics and Dynamical Astronomy
VL - 91
Y1 - 2005/1/1
SP - 151
EP - 171
KW - eccentric ringlets/ planetary rings
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005CeMDA..91..151M&db_key=AST&high=42a068d47526716
N2 - We use a simple model of the dynamics of a narrow-eccentric ring, to put
some constraints on some of the observable properties of the real
systems. In this work we concentrate on the case of the `Titan
ringlet of Saturn'.
ER -
TY - Journal
T1 - Helium Line Formation and Abundance in a Solar Active Region
A1 - Mauas, P. J. D.
A1 - Andretta, V.
A1 - Falchi, A.
A1 - Falciani, R.
A1 - Teriaca, L.
A1 - Cauzzi, G.
JO - Astrophysical Journal
VL - 619
Y1 - 2005/1/1
SP - 604
EP - 612
KW - Sun: Abundances/ Sun: Activity
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...619..604M&db_key=AST&high=42a068d47526716
N2 - An observing campaign (SOHO JOP 139), coordinated between ground-based
and Solar and Heliospheric Observatory (SOHO) instruments, has been
planned to obtain simultaneous spectroheliograms of the same active
region in several spectral lines. The chromospheric lines Ca II K,
Halpha, and Na I D, as well as He I 10830, 5876, 584, and He II 304
Å lines have been observed. The EUV radiation in the range
lambda<500 Å and in the range 2601×104 K. This region, between the chromosphere and
transition region, has been indicated as a good candidate for processes
that might be responsible for strong variations of [He]. The set of our
observables can still be well reproduced in both cases, changing the
atmospheric structure mainly in the low transition region. This implies
that, to choose between different values of [He], it is necessary to
constrain the transition region with different observables, independent
of the He lines.
ER -
TY - Journal
T1 - A catalogue of ultraluminous X-ray sources in external galaxies
A1 - Liu, Q. Z.
A1 - Mirabel, I. F.
JO - Astronomy and Astrophysics
VL - 429
Y1 - 2005/1/1
SP - 1125
EP - 1129
KW - X-rays: galaxies/ X-rays: binaries/ galaxies: general/ catalogs
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...429.1125L&db_key=AST&high=42a068d47526716
N2 - We present a catalogue of ultraluminous X-ray sources (ULXs) in external
galaxies. The aim of this catalogue is to provide easy access to the
properties of ULXs, their possible counterparts at other wavelengths
(optical, IR, and radio), and their host galaxies. The catalogue
contains 229 ULXs reported in the literature until April 2004. Most ULXs
are stellar-mass-black hole X-ray binaries, but it is not excluded that
some ULXs could be intermediate-mass black holes. A small fraction of
the candidate ULXs may be background Active Galactic Nuclei (AGN) and
Supernova Remnants (SNRs). ULXs with luminosity above 1040
ergs s-1 are found in both starburst galaxies and in the
halos of early-type galaxies.
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/429/1125
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=42a068d47526716
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 - The Galaxy Density Environment of Gamma-Ray Burst Host Galaxies
A1 - Bornancini, Carlos G.
A1 - Martínez, Héctor J.
A1 - Lambas, Diego G.
A1 - Le Floc'h, Emeric
A1 - Mirabel, I. Félix
A1 - Minniti, Dante
JO - Astrophysical Journal
VL - 614
Y1 - 2004/10/1
SP - 84
EP - 90
KW - Cosmology: Observations/ Gamma Rays: Bursts
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...614...84B&db_key=AST&high=42a068d47526716
N2 - We analyze cross-correlation functions between gamma-ray burst (GRB)
hosts and surrounding galaxies. We have used data obtained with the Very
Large Telescope at Cerro Paranal (Chile), as well as public Hubble Space
Telescope data. Our results indicate that GRB host galaxies do not
reside in high galaxy density environments. Moreover, the host
galaxy-galaxy cross-correlations show a relatively low amplitude. Our
results are in agreement with the cross-correlation function between
star forming galaxies and surrounding objects in the Hubble Deep
Field-North (HDF-N).
Based on observations with the Very Large Telescope, obtained at the
European Southern Observatory in Chile under proposal 67.B-0611(A).
Based on observations made with the NASA/ESA Hubble Space Telescope
(HST), obtained at the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy,
Inc. under NASA contract NAS5-2655.
ER -
TY - Journal
T1 - INTEGRAL observation of 3EG J1736-2908
A1 - Di Cocco, G.
A1 - Foschini, L.
A1 - Grandi, P.
A1 - Malaguti, G.
A1 - Castro-Tirado, A. J.
A1 - Chaty, S.
A1 - Dean, A. J.
A1 - Gehrels, N.
A1 - Grenier, I.
A1 - Hermsen, W.
A1 - Kuiper, L.
A1 - Lund, N.
A1 - Mirabel, F.
JO - Astronomy and Astrophysics
VL - 425
Y1 - 2004/10/1
SP - 89
EP - 93
KW - gamma-rays: observations/ X-rays: galaxies/ galaxies: active/ galaxies: individual: GRS1734-292
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...425...89D&db_key=AST&high=42a068d47526716
N2 - The possible identification by INTEGRAL of the EGRET source 3EG
J1736-2908 with the active galactic nucleus GRS 1734-292 is discussed.
The latter was discovered in 1990 and later identified with a Seyfert 1
galaxy. At the time of the compilation of the 3rd EGRET Catalog, it was
not considered as a possible counterpart of the source 3EG J1736-2908,
which remained unidentified. A detailed multiwavelength study of the
EGRET error circle is presented, by including archival radio, soft- and
hard-X observations, suggesting that GRS1734-292 could be a likely
counterpart of 3EG J1736-2908, even though this poses very interesting
questions about the production mechanisms of gamma-rays with energies
greater than 100 MeV.
Based on observations with INTEGRAL, an ESA project with instruments and
science data center funded by ESA member states (especially the PI
countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech
Republic and Poland, and with the participation of Russia and the USA.
ER -
TY - Journal
T1 - SN 2003lw and GRB 031203: A Bright Supernova for a Faint Gamma-Ray Burst
A1 - Malesani, D.
A1 - Tagliaferri, G.
A1 - Chincarini, G.
A1 - Covino, S.
A1 - Della Valle, M.
A1 - Fugazza, D.
A1 - Mazzali, P. A.
A1 - Zerbi, F. M.
A1 - D'Avanzo, P.
A1 - Kalogerakos, S.
A1 - Simoncelli, A.
A1 - Antonelli, L. A.
A1 - Burderi, L.
A1 - Campana, S.
A1 - Cucchiara, A.
A1 - Fiore, F.
A1 - Ghirlanda, G.
A1 - Goldoni, P.
A1 - Götz, D.
A1 - Mereghetti, S.
A1 - Mirabel, I. F.
A1 - Romano, P.
A1 - Stella, L.
A1 - Minezaki, T.
A1 - Yoshii, Y.
A1 - Nomoto, K.
JO - Astrophysical Journal
VL - 609
Y1 - 2004/7/1
SP - L5
EP - L8
KW - Gamma Rays: Bursts/ Stars: Supernovae: Individual: Alphanumeric: SN 2003lw
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...609L...5M&db_key=AST&high=42a068d47526716
N2 - Optical and near-infrared observations of the gamma-ray burst GRB
031203, at z=0.1055, are reported. A very faint afterglow is detected
superposed onto the host galaxy in our first infrared JHK observations,
carried out ~9 hr after the burst. Subsequently, a rebrightening is
detected in all bands, peaking in the R band about 18 rest-frame days
after the burst. The rebrightening closely resembles the light curve of
a supernova like SN 1998bw, assuming that the GRB and the SN went off
almost simultaneously, but with a somewhat slower evolution. Spectra
taken close to the maximum of the rebrightening show extremely broad
features as in SN 1998bw. The determination of the absolute magnitude of
this SN (SN 2003lw) is difficult owing to the large and uncertain
extinction, but likely this event was brighter than SN 1998bw by 0.5 mag
in the VRI bands, reaching an absolute magnitude
MV=-19.75+/-0.15.
ER -
TY - Journal
T1 - A microquasar shot out from its birth place
A1 - Mirabel, I. F.
A1 - Rodrigues, I.
A1 - Liu, Q. Z.
JO - Astronomy and Astrophysics
VL - 422
Y1 - 2004/7/1
SP - L29
EP - L32
KW - stars: individual: LS I +61°303
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...422L..29M&db_key=AST&high=42a068d47526716
N2 - We show that the microquasar LS I +61° 303 is running away from its
birth place in a young complex of massive stars. The supernova explosion
that formed the compact object shot out the X-ray binary with a linear
momentum of 430±140 M⊙ km s-1, which
is comparable to the linear momenta found in solitary runaway neutron
stars and millisecond pulsars. The properties of the binary system and
its runaway motion of 27±6 km s-1 imply that the natal
supernova was asymmetric and that the upper limit for the mass that
could have been suddenly ejected in the explosion is ~2
M⊙. The initial mass of the progenitor star of the
compact object that is inferred depends on whether the formation of
massive stars in the parent stellar cluster was coeval or a sequential
process.
ER -
TY - Journal
T1 - On the jet structure and magnetic field configuration of GRB 020813
A1 - Lazzati, D.
A1 - Covino, S.
A1 - Gorosabel, J.
A1 - Rossi, E.
A1 - Ghisellini, G.
A1 - Rol, E.
A1 - Castro Cerón, J. M.
A1 - Castro-Tirado, A. J.
A1 - Della Valle, M.
A1 - di Serego Alighieri, S.
A1 - Fruchter, A. S.
A1 - Fynbo, J. P. U.
A1 - Goldoni, P.
A1 - Hjorth, J.
A1 - Israel, G. L.
A1 - Kaper, L.
A1 - Kawai, N.
A1 - Le Floc'h, E.
A1 - Malesani, D.
A1 - Masetti, N.
A1 - Mazzali, P.
A1 - Mirabel, F.
A1 - Moller, P.
A1 - Ortolani, S.
A1 - Palazzi, E.
A1 - Pian, E.
A1 - Rhoads, J.
A1 - Ricker, G.
A1 - Salmonson, J. D.
A1 - Stella, L.
A1 - Tagliaferri, G.
A1 - Tanvir, N.
A1 - van den Heuvel, E.
A1 - Wijers, R. A. M. J.
A1 - Zerbi, F. M.
JO - Astronomy and Astrophysics
VL - 422
Y1 - 2004/7/1
SP - 121
EP - 128
KW - gamma rays: bursts/ polarization/ radiation mechanisms: non-thermal
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...422..121L&db_key=AST&high=42a068d47526716
N2 - The polarization curve of GRB 020813 is discussed and compared to
different models for the structure, evolution and magnetisation
properties of the jet and the interstellar medium onto which the
fireball impacts. GRB 020813 is best suited for this kind of analysis
for the smoothness of its afterglow light curve, ensuring the
applicability of current models. The polarization dataset allows us to
rule out the standard GRB jet, in which the energy and Lorentz factor
have a well defined value inside the jet opening angle and the magnetic
field is generated at the shock front. We explore alternative models
finding that a structured jet or a jet with a toroidal component of the
magnetic field can fit equally well the polarization curve. Stronger
conclusions cannot be drawn due to the incomplete sampling of the
polarization curve. A more dense sampling, especially at early times, is
required to pin down the structure of the jet and the geometry of its
magnetic field.
Based on observations collected at the European Southern Observatory,
Cerro Paranal (Chile), ESO programmes 69.D-0461(A) and 69.D-0701(A).
ER -
TY - Journal
T1 - GRB 020813: Polarization in the case of a smooth optical decay
A1 - Gorosabel, J.
A1 - Rol, E.
A1 - Covino, S.
A1 - Castro-Tirado, A. J.
A1 - Castro Cerón, J. M.
A1 - Lazzati, D.
A1 - Hjorth, J.
A1 - Malesani, D.
A1 - Della Valle, M.
A1 - di Serego Alighieri, S.
A1 - Fiore, F.
A1 - Fruchter, A. S.
A1 - Fynbo, J. P. U.
A1 - Ghisellini, G.
A1 - Goldoni, P.
A1 - Greiner, J.
A1 - Israel, G. L.
A1 - Kaper, L.
A1 - Kawai, N.
A1 - Klose, S.
A1 - Kouveliotou, C.
A1 - Le Floc'h, E.
A1 - Masetti, N.
A1 - Mirabel, F.
A1 - Möller, P.
A1 - Ortolani, S.
A1 - Palazzi, E.
A1 - Pian, E.
A1 - Rhoads, J.
A1 - Ricker, G.
A1 - Saracco, P.
A1 - Stella, L.
A1 - Tagliaferri, G.
A1 - Tanvir, N.
A1 - van den Heuvel, E.
A1 - Vietri, M.
A1 - Vreeswijk, P. M.
A1 - Wijers, R. A. M. J.
A1 - Zerbi, F. M.
JO - Astronomy and Astrophysics
VL - 422
Y1 - 2004/7/1
SP - 113
EP - 119
KW - gamma rays: bursts/ techniques: photometric/ techniques: polarimetric
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...422..113G&db_key=AST&high=42a068d47526716
N2 - We present the results of a VLT polarimetric monitoring campaign of the
GRB 020813 optical afterglow carried out in three nights, from 0.88 to
4.20 days after the gamma-ray event. The mean values of the degree of
linear polarization (P) and its position angle (theta) resulting from
our campaign are < P>=1.18 ± 0.10 % and < theta> =
148.7° ± 2.3°, after correcting for
Galactic interstellar polarization. Our VLT data set is most naturally
described by a constant degree of linear polarization and position
angle, nonetheless a slow theta evolution cannot be entirely ruled
out by our data. The VLT monitoring campaign did not reveal either a
significant theta rotation respect to the Keck spectropolarimetric
observations performed ~0.25 days after the GRB (Barth et al.
\cite{Bart03a}). However, < P> is a factor of two lower than the
polarization degree measured from Keck. Additionally, the VLT
polarization data allowed us to construct an accurate V-band light
curve. The V-band photometric data revealed a smooth light curve with a
break located between the last Keck and our first VLT polarimetric
measurement, 0.33 < tbreak, V < 0.88 days after the
GRB. The typical magnitude fluctuations of the VLT V-band lightcurve are
0.003 mag, 0.010 mag and 0.016 mag for our three observing nights,
respectively. We speculate that the stability of theta might be
related to the smoothness of the light curve.
Based on observations collected at the European Southern Observatory,
Cerro Paranal (Chile), ESO programmes 69.D-0461(A) and 69.D-0701(A).
ER -
TY - Journal
T1 - GRB 030131: a long Gamma-Ray Burst detected with INTEGRAL during a satellite slew
A1 - Götz, D.
A1 - Mereghetti, S.
A1 - Hurley, K.
A1 - Deluit, S.
A1 - Feroci, M.
A1 - Frontera, F.
A1 - Fruchter, A.
A1 - Gorosabel, J.
A1 - Hartmann, D. H.
A1 - Hjorth, J.
A1 - Hudec, R.
A1 - Mirabel, I. F.
A1 - Pian, E.
A1 - Pizzichini, G.
A1 - Ubertini, P.
A1 - Winkler, C.
JO - Nuclear Physics B Proceedings Supplements
VL - 132
Y1 - 2004/6/1
SP - 316
EP - 319
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004NuPhS.132..316G&db_key=AST&high=42a068d47526716
N2 - Electronic Article Available from Elsevier Science.
ER -
TY - Journal
T1 - Chromospheric Models of Solar Type Stars: The Vaughan-Preston Gap
A1 - Vieytes, M.
A1 - Mauas, P. J. D.
JO - Astrophysics and Space Science
VL - 290
Y1 - 2004/4/1
SP - 311
EP - 318
KW - stars: atmospheres/ stars: activity/ stars: solar-type
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..311V&db_key=AST&high=42a068d47526716
N2 - We have built different models for stars of the same spectral type than
the Sun but with different levels of chromospheric activity, to study
the response of the S index of activity built from the emission of the
Ca II H and K lines to changes in the chromospheric structure. We found
that the fact that there are many stars with either strong or weak
emission, but few with intermediate values of S, the so-called Vaughan
Preston gap, can be due to a discontinuity in the response of the Ca II
lines to chromospheric heating. In fact, we are able to reproduce the
observed distribution of the number of stars as a function of S.
ER -
TY - Journal
T1 - Spectral evolution of weak bursts from SGR 1806-20 observed with INTEGRAL
A1 - Götz, D.
A1 - Mereghetti, S.
A1 - Mirabel, I. F.
A1 - Hurley, K.
JO - Astronomy and Astrophysics
VL - 417
Y1 - 2004/4/1
SP - L45
EP - L48
KW - gamma rays: bursts/ gamma rays: observations/ pulsars: general/ stars: individual: SGR 1806-20
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...417L..45G&db_key=AST&high=42a068d47526716
N2 - We report on bursts from the Soft Gamma-Ray Repeater SGR 1806-20
detected with INTEGRAL in October 2003, during a period of moderate
activity of the source. The spectral and temporal properties of 21 short
bursts are consistent with those found in previous observations, even if
these bursts are among the faintest observed in the 15-200 keV range
from this source. During some of the bursts a clear spectral evolution
is visible. The data also show, for the first time, evidence for a
hardness-intensity anti-correlation within SGR 1806-20 bursts.
Based on observations with INTEGRAL, an ESA project with instruments and
science data centre funded by ESA member states (especially the PI
countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech
Republic and Poland, and with the participation of Russia and the USA.
ER -
TY - Journal
T1 - Dust enshrouded star-forming activity in Arp 299
A1 - Gallais, P.
A1 - Charmandaris, V.
A1 - Le Floc'h, E.
A1 - Mirabel, I. F.
A1 - Sauvage, M.
A1 - Vigroux, L.
A1 - Laurent, O.
JO - Astronomy and Astrophysics
VL - 414
Y1 - 2004/2/1
SP - 845
EP - 855
KW - stars: formation/ galaxies: individual: Arp 299/ galaxies: individual: Mrk 171/ galaxies: interactions
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...414..845G&db_key=AST&high=42a068d47526716
N2 - We present mid-infrared spectro-imaging (5-16 mum) observations of the
infrared luminous interacting system Arp 299 (= Mrk 171 = IC 694+NGC
3690) obtained with the ISOCAM instrument aboard ISO. Our observations
show that nearly 40% of the total emission at 7 and 15 mum is diffuse,
originating from the interacting disks of the galaxies. Moreover, they
indicate the presence of large amounts of hot dust in the main infrared
sources of the system and large extinctions toward the nuclei. While the
observed spectra have an overall similar shape, mainly composed of
Unidentified Infrared Bands (UIB) in the short wavelength domain, a
strong continuum at ~13 mum and a deep silicate absorption band at
10 mum, their differences reveal the varying physical conditions of
each component. For each source, the spectral energy distribution (SED)
can be reproduced by a linear combination of a UIB ``canonical''
spectral template and a hot dust continuum due to a 230-300 K black
body, after independently applying an extinction correction to both of
them. We find that the UIB extinction does not vary much throughout the
system (AV î«¥ 5 mag) suggesting that most UIBs originate
from less enshrouded regions. IC 694 appears to dominate the infrared
emission of the system and our observations support the interpretation
of a deeply embedded nuclear starburst located behind an absorption of
about 40 magnitudes. The central region of NGC 3690 displays a hard
radiation field characterized by a [NeIII]/[NeII] ratio ≥1.8. It
also hosts a strong continuum from 5 to 16 mum which can be explained
as thermal emission from a deeply embedded (AV~60 mag)
compact source, consistent with the mid-infrared signature of an active
galactic nucleus (AGN), and in agreement with recent X-ray findings.
Based on observations with ISO, an ESA project with instruments funded
by ESA Member States (especially the PI countries: France, Germany, The
Netherlands and the UK) with the participation of ISAS and NASA.
ER -
TY - Journal
T1 - A Bias in Optical Observations of High-Redshift Luminous Infrared Galaxies
A1 - Charmandaris, V.
A1 - Le Floc'h, E.
A1 - Mirabel, I. F.
JO - Astrophysical Journal
VL - 600
Y1 - 2004/1/1
SP - L15
EP - L18
KW - Galaxies: High-Redshift/ Galaxies: Individual: Name: Arp 299/ Galaxies: Individual: Alphanumeric: VV 114/ Galaxies: Starburst/ Infrared: Galaxies/ Ultraviolet: Galaxies
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...600L..15C&db_key=AST&high=42a068d47526716
N2 - We present evidence for the dramatically different morphology between
the rest-frame UV and 7 mum mid-IR emission of VV 114 and Arp 299, two
nearby (z~0) violently interacting luminous infrared galaxies (LIRGs).
Nearly all LIRGs are interacting systems, and it is currently accepted
that they dominate the IR emission at z>1. LIRGs located at z=1-2
could easily be detected as unresolved sources in deep optical/near-IR
ground-based surveys as well as in upcoming 24 mum surveys with the
Space Infrared Telescope Facility. We demonstrate that the spatial
resolution of these surveys will result in blending of the emission from
unresolved interacting components. An increased scatter will thus be
introduced in the observed optical-to-mid-IR colors of these galaxies,
leading to a systematic underestimation of their dust content.
ER -
TY - Journal
T1 - CaII K interstellar observations towards early-type disc and halo stars
A1 - Smoker, J. V.
A1 - Rolleston, W. R. J.
A1 - Kay, H. R. M.
A1 - Kilkenny, D.
A1 - Morras, R.
A1 - Arnal, M.
A1 - Keenan, F. P.
A1 - Mooney, C. J.
A1 - Dufton, P. L.
A1 - Ryans, R. S. I.
A1 - Hambly, N. C.
A1 - O'Donoghue, D.
A1 - McGillivray, H.
JO - Monthly Notices of the Royal Astronomical Society
VL - 346
Y1 - 2003/11/1
SP - 119
EP - 134
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.346..119S&db_key=AST&high=42a068d47526716
N2 - We present high-resolution (R=lambda/Deltalambda~ 40000) CaII K
interstellar observations (lambdaair= 3933.66Å)
towards 88 mainly B-type stars, of which 74 are taken from the
Edinburgh-Cape or Palomar-Green surveys, and 81 have |b| > 25°.
The majority of the data come from previously existing spectroscopy,
although also included are 18 new observations of stars with echelle
spectra taken with UVES on the Very Large Telescope UT2 (Kueyen). Some
49 of the sample stars have distance estimates above the Galactic plane
(|z|) >= 1 kpc, and are thus good probes of the halo interstellar
medium. Of the 362 interstellar Ca K components that we detect, 75 (21
per cent) have absolute values of their LSR velocity values exceeding 40
km s-1. In terms of the deviation velocity for the sightlines
with distance estimates, 46/273 (17 per cent) of components have
velocity values exceeding those predicted by standard Galactic rotation
by more than 40 km s-1. Combining this data set with previous
observations, we find that the median value of the reduced equivalent
width (REW) of stars with |z| >= 1 kpc (EW×sin|b|) is ~115
mÅ (n= 80), similar to that observed in extragalactic sightlines
by Bowen. Using data of all z distances, the REW at infinity is found to
be ~130 mÅ, with the scaleheight (l) of the CaII K column density
distribution being ~800 pc (n= 196) and reduced column density at
infinity of log[N(CaII K) cm-2]~12.24. This implies that ~30
per cent of CaII K absorption occurs at distances exceeding ~1 kpc. For
nine sightlines with distance exceeding 1 kpc and with a companion
object within 5°, we find that all but two have values of CaII
reduced equivalent width the same to within ~20 per cent, when the REW
of the nearest object is extrapolated to the distance of the further of
the pair, and assuming l= 800 pc. For 29 of our sightlines with |z|
>= 1 kpc and a HI detection from the Leiden-Dwingeloo survey
(beamsize of 0.5°), we find log(N(CaII K)/N(HI)) ranging from -7.4
to -8.4. Values of the CaII K abundance relative to neutral hydrogen
(log[N(CaIIK)cm-2]-log[N(HI)cm-2]) are found to be
more than ~0.5dex higher in stars with distances exceeding ~100 pc, when
compared with the (log[N(CaII K) cm-2]-
log[N(Htot) cm-2]) values found in nearby
sightlines such as those in Wakker & Mathis (2000). Finally, stellar
CaII K equivalent widths of the sample are determined for 26 objects.
ER -
TY - Journal
T1 - First INTEGRAL observations of GRS 1915+105
A1 - Hannikainen, D. C.
A1 - Vilhu, O.
A1 - Rodriguez, J.
A1 - Brandt, S.
A1 - Westergaard, N. J.
A1 - Lund, N.
A1 - Mocoeur, I.
A1 - Durouchoux, Ph.
A1 - Belloni, T.
A1 - Castro-Tirado, A.
A1 - Charles, P. A.
A1 - Dean, A. J.
A1 - Fender, R. P.
A1 - Feroci, M.
A1 - Hakala, P.
A1 - Hunstead, R. W.
A1 - Kaiser, C. R.
A1 - King, A.
A1 - Mirabel, I. F.
A1 - Pooley, G. G.
A1 - Poutanen, J.
A1 - Wu, K.
A1 - Zdziarski, A. A.
JO - Astronomy and Astrophysics
VL - 411
Y1 - 2003/11/1
SP - L415
EP - L419
KW - X-rays: binaries/ X-rays: GRS 1915+105
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...411L.415H&db_key=AST&high=42a068d47526716
N2 - We present data from the first of six monitoring Open Time observations
of GRS 1915+105 undertaken with the orbiting INTEGRAL satellite. The
source was clearly detected with all three X-ray and gamma-ray
instruments on board. GRS 1915+105 was in a highly variable state, as
demonstrated by the JEM X-2 and ISGRI lightcurves. These and
simultaneous RXTE/PCA lightcurves point to a novel type of variability
pattern in the source. In addition, we fit the combined JEM X-2 and
ISGRI spectrum between 3-300 keV with a disk blackbody + powerlaw model
leading to typical parameter values found earlier at similar luminosity
levels. A new transient, IGR J19140+098, was discovered during the
present observation.
Based on observations with INTEGRAL, an ESA project with instruments and
science data center funded by ESA and member states (especially the PI
countries: Denmark, France, Germany, Italy, Switzerland, and Spain), the
Czech Republic, and Poland and with the participation of Russia and the
US.
ER -
TY - Journal
T1 - IBIS: The Imager on-board INTEGRAL
A1 - Ubertini, P.
A1 - Lebrun, F.
A1 - Di Cocco, G.
A1 - Bazzano, A.
A1 - Bird, A. J.
A1 - Broenstad, K.
A1 - Goldwurm, A.
A1 - La Rosa, G.
A1 - Labanti, C.
A1 - Laurent, P.
A1 - Mirabel, I. F.
A1 - Quadrini, E. M.
A1 - Ramsey, B.
A1 - Reglero, V.
A1 - Sabau, L.
A1 - Sacco, B.
A1 - Staubert, R.
A1 - Vigroux, L.
A1 - Weisskopf, M. C.
A1 - Zdziarski, A. A.
JO - Astronomy and Astrophysics
VL - 411
Y1 - 2003/11/1
SP - L131
EP - L139
KW - INTEGRAL/ IBIS/ gamma-ray imaging
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...411L.131U&db_key=AST&high=42a068d47526716
N2 - The IBIS telescope is the high angular resolution gamma-ray imager
on-board the INTEGRAL Observatory, successfully launched from Baikonur
(Kazakhstan) the 17{th} of October 2002. This medium size ESA project,
planned for a 2 year mission with possible extension to 5, is devoted to
the observation of the gamma-ray sky in the energy range from 3 keV to
10 MeV (Winkler \cite{Winkler01}). The IBIS imaging system is based on
two independent solid state detector arrays optimised for low (15-1000
keV) and high (0.175-10.0 MeV) energies surrounded by an active VETO
System. This high efficiency shield is essential to minimise the
background induced by high energy particles in the highly excentric out
of van Allen belt orbit. A Tungsten Coded Aperture Mask, 16 mm thick and
~ 1 squared meter in dimension is the imaging device. The IBIS telescope
will serve the scientific community at large providing a unique
combination of unprecedented high energy wide field imaging capability
coupled with broad band spectroscopy and high resolution timing over the
energy range from X to gamma rays. To date the IBIS telescope is working
nominally in orbit since more than 9 month.
ER -
TY - Journal
T1 - Relativistic jets in the universe
A1 - Mirabel, I. F.
JO - New Astronomy Review
VL - 47
Y1 - 2003/10/1
SP - 471
EP - 475
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003NewAR..47..471M&db_key=AST&high=42a068d47526716
N2 - Relativistic outflows are a common phenomenon in accreting black holes.
Despite the enormous differences in scale, stellar-mass black holes in
X-ray binaries and collapsars, and super-massive black holes at the
dynamic centre of galaxies are sources of jets with analogous physical
properties. Synergism between the research on microquasars, gamma-ray
bursts, and Active Galactic Nuclei should help to gain insight into the
physics of relativistic jets seen everywhere in the Universe.
ER -
TY - Journal
T1 - Simultaneous multi-wavelength observations of GRS 1915+105
A1 - Fuchs, Y.
A1 - Rodriguez, J.
A1 - Mirabel, I. F.
A1 - Chaty, S.
A1 - Ribó, M.
A1 - Dhawan, V.
A1 - Goldoni, P.
A1 - Sizun, P.
A1 - Pooley, G. G.
A1 - Zdziarski, A. A.
A1 - Hannikainen, D. C.
A1 - Kretschmar, P.
A1 - Cordier, B.
A1 - Lund, N.
JO - Astronomy and Astrophysics
VL - 409
Y1 - 2003/10/1
SP - L35
EP - L39
KW - stars: individual: GRS 1915+105/ X-rays: binaries/ gamma rays: observations/ ISM: jets and outflows
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...409L..35F&db_key=AST&high=42a068d47526716
N2 - We present the result of multi-wavelength observations of the
microquasar GRS 1915+105 in a plateau state with a luminosity of ~
7.5*E38 erg s-1 ( ~ 40% L_Edd), conducted
simultaneously with the INTEGRAL and RXTE satellites, the ESO/NTT, the
Ryle Telescope, the NRAO VLA and VLBA, in 2003 April 2-3. For the first
time were observed concurrently in GRS 1915+105 all of the following
properties: a strong steady optically thick radio emission corresponding
to a powerful compact jet resolved with the VLBA, bright near-IR
emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated
spectrum without any cutoff in the 3-400 keV range.
Based on observations with INTEGRAL, an ESA project with instruments and
science data centre funded by ESA member states (especially the PI
countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech
Republic and Poland, and with the participation of Russia and the USA.
Based on observations collected at the European Southern Observatory,
Chile (ESO N° 071.D-0073).
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc.
ER -
TY - Journal
T1 - Observation of GRB 030131 with the INTEGRAL satellite
A1 - Götz, D.
A1 - Mereghetti, S.
A1 - Hurley, K.
A1 - Deluit, S.
A1 - Feroci, M.
A1 - Frontera, F.
A1 - Fruchter, A.
A1 - Gorosabel, J.
A1 - Hartmann, D. H.
A1 - Hjorth, J.
A1 - Hudec, R.
A1 - Mirabel, I. F.
A1 - Pian, E.
A1 - Pizzichini, G.
A1 - Ubertini, P.
A1 - Winkler, C.
JO - Astronomy and Astrophysics
VL - 409
Y1 - 2003/10/1
SP - 831
EP - 834
KW - gamma rays: bursts/ gamma rays: observations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...409..831G&db_key=AST&high=42a068d47526716
N2 - A long Gamma-Ray Burst (GRB) was detected with the instruments on board
the INTEGRAL satellite on January 31 2003. Although most of the GRB,
which lasted ~ 150 s, occurred during a satellite slew, the automatic
software of the INTEGRAL Burst Alert System was able to detect it in
near-real time. Here we report the results obtained with the IBIS
instrument, which detected GRB 030131 in the 15 keV-200 keV energy
range, and ESO/VLT observations of its optical transient. The burst
displays a complex time profile with numerous peaks. The peak spectrum
can be described by a single power law with photon index Gamma =~ 1.7
and has a flux of ~ 2 photons cm-2 s-1 in the
20-200 keV energy band. The high sensitivity of IBIS has made it
possible for the first time to perform detailed time-resolved
spectroscopy of a GRB with a fluence of 7*E-6 erg
cm-2 (20-200 keV).
Based on observations with INTEGRAL, an ESA project with instruments and
science data centre funded by ESA member states (especially the PI
countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech
Republic and Poland, and with the participation of Russia and the USA,
and on observations collected by the Gamma-Ray Burst Collaboration at
ESO (GRACE) at the European Sourthern Observatory, Paranal, Chile
(Programme 70.D-0523).
ER -
TY - Journal
T1 - Optical and near-infrared observations of the microquasar V4641 Sgr during the 1999 September outburst
A1 - Chaty, S.
A1 - Charles, P. A.
A1 - Martí, J.
A1 - Mirabel, I. F.
A1 - Rodríguez, L. F.
A1 - Shahbaz, T.
JO - Monthly Notices of the Royal Astronomical Society
VL - 343
Y1 - 2003/7/1
SP - 169
EP - 174
KW - stars: individual: V4641 Sgr/ stars: individual: SAX J1819.3: 2525/ stars: individual: XTE J1819: 254/ ISM: jets and outflows/ infrared: stars/ X-rays: binaries
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.343..169C&db_key=AST&high=42a068d47526716
N2 - We present photometric and spectroscopic optical and near-infrared (NIR)
observations taken during the outburst of the microquasar V4641 Sgr =
SAX J1819.3 - 2525 in 1999 September. We observed an increase in the
J-Ks colour between 5 and 8 d after the outburst, which we
interpret as likely evidence for the presence of dust around the source.
We also observed an extraordinarily strong, broad and variable Halpha
line, with a velocity width of 4560 km s-1, suggesting the
presence of a high-velocity outflow component. We constrain the distance
of the system between 3 and 8 kpc, locating it further away than
previously derived from radio observations, but consistent with results
from Orosz et al. We then discuss the nature of this system, showing
that the companion star is either a B3-A2 main-sequence star or a B3-A2
subgiant crossing the Hertzsprung gap. The system is therefore an
intermediate- or high-mass X-ray binary system (IMXB or HMXB). The
distance derived by these optical/NIR observations implies that the jets
observed by Hjellming et al. would then exhibit apparent velocities of
~10c. We finally discuss the possibility of an interaction between the
jets and surroundings of the source, and also of this source being a
`microblazar'.
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=42a068d47526716
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 - Mid-infrared observations of GRS 1915+105 during plateau and flaring states
A1 - Fuchs, Y.
A1 - Mirabel, I. F.
A1 - Claret, A.
JO - Astronomy and Astrophysics
VL - 404
Y1 - 2003/6/1
SP - 1011
EP - 1021
KW - stars: individual: GRS 1915+105/ X-rays: binaries/ infrared: stars/ stars: circumstellar matter/ ISM: jets and outflows/ stars: winds/ outflows
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...404.1011F&db_key=AST&high=42a068d47526716
N2 - We present mid-infrared (4-18 mu m) observations of the microquasar GRS
1915+105 obtained with ISOCAM, the camera on board the Infrared Space
Observatory (ISO), in 1996 April and 1997 October. The first observation
probably occurred during a flaring event with oscillating synchrotron
emission. The 1997 observation occurred a few days before a major
relativistic ejection, during a plateau state of inverted-spectrum radio
emission and hard quasi-stable X-ray emission. The K-M giant donor star
in GRS 1915+105 cannot account for the mid-IR emission and we discuss
the possible additional components depending on two absorption laws.
Thermal emission from dust seems unlikely. The flat mid-IR spectrum
obtained during the plateau state is likely to be synchrotron emission.
It would be the first evidence of the infrared extension of the radio
synchrotron emission from the compact jets, although optically thin
free-free emission from an X-ray driven-wind from the accretion disc
cannot be excluded.
ER -
TY - Journal
T1 - Formation of a Black Hole in the Dark
A1 - Mirabel, I. Félix
A1 - Rodrigues, Irapuan
JO - Science
VL - 300
Y1 - 2003/5/1
SP - 1119
EP - 1121
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Sci...300.1119M&db_key=AST&high=42a068d47526716
N2 - We show that the black hole in the x-ray binary Cygnus X-1 was formed in
situ and did not receive an energetic trigger from a nearby supernova.
The progenitor of the black hole had an initial mass greater than 40
solar masses, and during the collapse to form the ~10-solar mass black
hole of Cygnus X-1, the upper limit for the mass that could have been
suddenly ejected is ~1 solar mass, much less than the mass ejected in a
supernova. The observations suggest that high-mass stellar black holes
may form promptly, when massive stars disappear silently.
ER -
TY - Journal
T1 - The plane of the Edgeworth-Kuiper belt
A1 - Collander-Brown, Simon J.
A1 - Melita, Mario D.
A1 - Williams, Iwan P.
A1 - Fitzsimmons, Alan
JO - Icarus
VL - 162
Y1 - 2003/3/1
SP - 22
EP - 26
KW - Transneptunian objects/ Planetary dynamics/ Orbits/ Origin/ Solar System
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Icar..162...22C&db_key=AST&high=42a068d47526716
N2 - We examine possible locations for the primordial disk of the
Edgeworth-Kuiper Belt (EKB), using several subsets of the known objects
as markers of the total mass distribution. Using a secular perturbation
theory, we find that the primordial plane of the EKB could have remained
thin enough to escape detection only if it is clustered very closely
about the invariable plane of the Solar System.
ER -
TY - Journal
T1 - Polarization evolution of the GRB 020405 afterglow
A1 - Covino, S.
A1 - Malesani, D.
A1 - Ghisellini, G.
A1 - Lazzati, D.
A1 - di Serego Alighieri, S.
A1 - Stefanon, M.
A1 - Cimatti, A.
A1 - Della Valle, M.
A1 - Fiore, F.
A1 - Goldoni, P.
A1 - Kawai, N.
A1 - Israel, G. L.
A1 - Le Floc'h, E.
A1 - Mirabel, I. F.
A1 - Ricker, G.
A1 - Saracco, P.
A1 - Stella, L.
A1 - Tagliaferri, G.
A1 - Zerbi, F. M.
JO - Astronomy and Astrophysics
VL - 400
Y1 - 2003/3/1
SP - L9
EP - L12
KW - gamma rays: bursts/ polarization/ radiation mechanisms: non-thermal
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...400L...9C&db_key=AST&high=42a068d47526716
N2 - Polarization measurements for the optical counterpart to GRB 020405 are
presented and discussed. Our observations were performed with the
VLT-UT3 (Melipal) during the second and third night after the gamma-ray
burst discovery. The polarization degree (and the position angle)
appears to be constant between our two observations at a level around
1.5/2%. The polarization can be intrinsic but it is not possible to
unambiguously exclude that a substantial fraction of it is induced by
dust in the host galaxy.
Based on observations made with ESO telescopes at the Paranal
Observatory under programme Id 69.D-0461.
ER -
TY - Journal
T1 - Are the hosts of gamma-ray bursts sub-luminous and blue galaxies?
A1 - Le Floc'h, E.
A1 - Duc, P.-A.
A1 - Mirabel, I. F.
A1 - Sanders, D. B.
A1 - Bosch, G.
A1 - Diaz, R. J.
A1 - Donzelli, C. J.
A1 - Rodrigues, I.
A1 - Courvoisier, T. J.-L.
A1 - Greiner, J.
A1 - Mereghetti, S.
A1 - Melnick, J.
A1 - Maza, J.
A1 - Minniti, D.
JO - Astronomy and Astrophysics
VL - 400
Y1 - 2003/3/1
SP - 499
EP - 510
KW - galaxies: starburst/ galaxies: evolution/ cosmology: observations/ gamma rays: bursts
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...400..499L&db_key=AST&high=42a068d47526716
N2 - We present K-band imaging observations of ten gamma-ray burst (GRB) host
galaxies for which an optical and/or radio afterglow associated with the
GRB event was clearly identified. Data were obtained with the Very Large
Telescope and New Technology Telescope at ESO (Chile), and with the
Gemini-North telescope at Mauna Kea (Hawaii). Adding to our sample nine
other GRB hosts with K-band photometry and determined redshifts
published in the literature, we compare their observed and absolute K
magnitudes as well as their R-K colours with those of other distant
sources detected in various optical, near-infrared, mid-infrared and
submillimeter deep surveys. We find that the GRB host galaxies, most of
them lying at 0.5<~ z la1 .5, exhibit very blue colours, comparable
to those of the faint blue star-forming sources at high redshift. They
are sub-luminous in the K-band, suggesting a low stellar mass content.
We do not find any GRB hosts harbouring R- and K-band properties similar
to those characterizing the luminous infrared/submillimeter sources and
the extremely red starbursts. Should GRBs be regarded as an unbiased
probe of star-forming activity, this lack of luminous and/or reddened
objects among the GRB host sample might reveal that the detection of GRB
optical afterglows is likely biased toward unobscured galaxies. It would
moreover support the idea that a large fraction of the optically-dark
GRBs occur within dust-enshrouded regions of star formation. On the
other hand, our result might also simply reflect intrinsic properties of
GRB host galaxies experiencing a first episode of very massive star
formation and characterized by a rather weak underlying stellar
population. Finally, we compute the absolute B magnitudes for the whole
sample of GRB host galaxies with known redshifts and detected at optical
wavelengths. We find that the latter appear statistically even less
luminous than the faint blue sources which mostly contributed to the
B-band light emitted at high redshift. This indicates that the formation
of GRBs could be favoured in particular systems with very low
luminosities and, therefore, low metallicities. Such an intrinsic bias
toward metal-poor environments would be actually consistent with what
can be expected from the currently-favoured scenario of the
``collapsar''. The forthcoming launch of the SWIFT mission at the end of
2003 will provide a dramatic increase of the number of GRB-selected
sources. A detailed study of the chemical composition of the gas within
this sample of galaxies will thus allow us to further analyse the
potential effect of metallicity in the formation of GRB events.
Based on observations with the Very Large Telescope, obtained at the
European Southern Observatory in Chile under proposal 67.B-0611(A).
Based on observations with the Gemini-North Telescope, obtained at Mauna
Kea (Hawaii) under proposal GN-2001A-Q-58.
Appendix A is only available in electronic form at
http://www.edpsciences.org
ER -
TY - Journal
T1 - ISOCAM view of the starburst galaxies M 82, NGC 253 and NGC 1808
A1 - Förster Schreiber, N. M.
A1 - Sauvage, M.
A1 - Charmandaris, V.
A1 - Laurent, O.
A1 - Gallais, P.
A1 - Mirabel, I. F.
A1 - Vigroux, L.
JO - Astronomy and Astrophysics
VL - 399
Y1 - 2003/3/1
SP - 833
EP - 855
KW - galaxies: individual: M 82/ NGC 253/ NGC 1808/ galaxies: ISM/ galaxies: starburst/ infrared: galaxies/ infrared: ISM
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...399..833F&db_key=AST&high=42a068d47526716
N2 - We present results of mid-infrared lambda = 5.0-16.5 mum
spectrophotometric imaging of the starburst galaxies M
82, NGC 253, and NGC
1808 from the ISOCAM instrument on board the Infrared Space
Observatory. The mid-infrared spectra of the three galaxies are very
similar in terms of features present. The lambda >~ 11 mum
continuum attributed to very small dust grains (VSGs) exhibits a large
spread in intensity relative to the short-wavelength emission. We find
that the 15 mu m dust continuum flux density correlates well with the
fine-structure [Ar Ii] 6.99 mu m line flux and thus provides a good
quantitative indicator of the level of star formation activity. By
contrast, the lambda = 5-11 mum region dominated by emission from
polycyclic aromatic hydrocarbons (PAHs) has a nearly invariant shape.
Variations in the relative intensities of the PAH features are
nevertheless observed, at the 20%-100% level. We illustrate extinction
effects on the shape of the mid-infrared spectrum of obscured
starbursts, emphasizing the differences depending on the applicable
extinction law and the consequences for the interpretation of PAH ratios
and extinction estimates. The relative spatial distributions of the PAH,
VSG, and [Ar Ii] 6.99 mu m emission between the three galaxies exhibit
remarkable differences. The la 1 kpc size of the mid-infrared source is
much smaller than the optical extent of our sample galaxies and 70%-100%
of the IRAS 12 mu m flux is recovered within the ISOCAM <= 1.5
arcmin2 field of view, indicating that the nuclear starburst
dominates the total mid-infrared emission while diffuse light from
quiescent disk star formation contributes little.
Based on observations with ISO, an ESA project with instruments funded
by ESA member states (especially the PI countries: France, Germany, The
Netherlands, and the UK), and with participation of ISAS and NASA.
ER -
TY - Journal
T1 - The origin of Scorpius X-1
A1 - Mirabel, I. F.
A1 - Rodrigues, I.
JO - Astronomy and Astrophysics
VL - 398
Y1 - 2003/2/1
SP - L25
EP - L28
KW - stars: individual: Scorpius X-1/ X-rays: binaries/ astrometry
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...398L..25M&db_key=AST&high=42a068d47526716
N2 - We have used multi-wavelength observations of high precision to derive
the space velocity and compute the orbit around the Galactic Centre of
the prototype X-ray binary Scorpius X-1. An origin in the local spiral
arm of the Milky Way is ruled out. The galactocentric kinematics of
Scorpius X-1 is similar to that of the most ancient stars and globular
clusters of the inner Galactic halo. Most probably, this low-mass X-ray
binary was formed by a close encounter in a globular cluster. However,
it cannot be ruled out that a natal supernova explosion launched
Scorpius X-1 into an orbit like this from a birth place in the galactic
bulge. In any case, the Galactocentric orbit indicates that Scorpius X-1
was formed more than 30 Myrs ago.
ER -
TY - Journal
T1 - Les microquasars.
A1 - Mirabel, F.
JO - Pour la Science
VL - 307
Y1 - 2003/1/1
SP - 54
EP - 61
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003PSci..307...54M&db_key=AST&high=42a068d47526716
N2 - Not Available
ER -
TY - Journal
T1 - Systems of galaxies in the Sloan Digital Sky Survey: the fundamental plane
A1 - Díaz, Eugenia
A1 - Muriel, Hernán
JO - Monthly Notices of the Royal Astronomical Society
Y1 - 2005/11/1
SP - 997
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.tmp..997D&db_key=AST&high=42a068d47531548
N2 - We analyse a subsample of the galaxy groups recently obtained by
Merchán & Zandivarez from the SDSS DR3 to study the
fundamental plane and the mass-to-light ratio of galaxy groups. We find
a fundamental plane given by
LR~R1.3sigma0.7. We do not find
differences when different dynamical states or redshift ranges are
analysed. We find that the mass-to-light ratio increases with group mass
as M/LR~M0.36.
ER -
TY - Journal
T1 - Afterglows, Redshifts, and Properties of Swift Gamma-Ray Bursts
A1 - Berger, E.
A1 - Kulkarni, S. R.
A1 - Fox, D. B.
A1 - Soderberg, A. M.
A1 - Harrison, F. A.
A1 - Nakar, E.
A1 - Kelson, D. D.
A1 - Gladders, M. D.
A1 - Mulchaey, J. S.
A1 - Oemler, A.
A1 - Dressler, A.
A1 - Cenko, S. B.
A1 - Price, P. A.
A1 - Schmidt, B. P.
A1 - Frail, D. A.
A1 - Morrell, N.
A1 - Gonzalez, S.
A1 - Krzeminski, W.
A1 - Sari, R.
A1 - Gal-Yam, A.
A1 - Moon, D.-S.
A1 - Penprase, B. E.
A1 - Jayawardhana, R.
A1 - Scholz, A.
A1 - Rich, J.
A1 - Peterson, B. A.
A1 - Anderson, G.
A1 - McNaught, R.
A1 - Minezaki, T.
A1 - Yoshii, Y.
A1 - Cowie, L. L.
A1 - Pimbblet, K.
JO - Astrophysical Journal
VL - 634
Y1 - 2005/11/1
SP - 501
EP - 508
KW - Gamma Rays: Bursts
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...634..501B&db_key=AST&high=42a068d47531548
N2 - We present optical, near-IR, and radio follow-up of 16 Swift bursts,
including our discovery of nine afterglows and a redshift determination
for three. These observations, supplemented by data from the literature,
provide an afterglow recovery rate of 52% in the optical/near-IR, much
higher than in previous missions (BeppoSAX, HETE-2, INTEGRAL, and IPN).
The optical/near-IR afterglows of Swift events are on average 1.8 mag
fainter at t=12 hr than those of previous missions. The X-ray afterglows
are similarly fainter than those of pre-Swift bursts. In the radio the
limiting factor is the VLA threshold, and the detection rate for Swift
bursts is similar to that for past missions. The redshift distribution
of pre-Swift bursts peaked at z~1, whereas the six Swift bursts with
measured redshifts are distributed evenly between 0.7 and 3.2. From
these results we conclude that (1) the pre-Swift distributions were
biased in favor of bright events and low-redshift events, (2) the higher
sensitivity and accurate positions of Swift result in a better
representation of the true burst redshift and brightness distributions
(which are higher and dimmer, respectively), and (3) ~10% of the bursts
are optically dark, as a result of a high redshift and/or dust
extinction. We remark that the apparent lack of low-redshift,
low-luminosity Swift bursts and the lower event rate than prelaunch
estimates (90 vs. 150 per year) are the result of a threshold that is
similar to that of BATSE. In view of these inferences, afterglow
observers may find it advisable to make significant changes in follow-up
strategies of Swift events. The faintness of the afterglows means that
large telescopes should be employed as soon as the burst is localized.
Sensitive observations in RIz and near-IR bands will be needed to
discriminate between a typical z~2 burst with modest extinction and a
high-redshift event. Radio observations will be profitable for a small
fraction (~10%) of events. Finally, we suggest that a search for bright
host galaxies in untriggered BAT localizations may increase the chance
of finding nearby low-luminosity GRBs.
ER -
TY - Journal
T1 - Redshifts in the Southern Abell Redshift Survey Clusters. I. The Data
A1 - Way, M. J.
A1 - Quintana, H.
A1 - Infante, L.
A1 - Lambas, D. G.
A1 - Muriel, H.
JO - Astronomical Journal
VL - 130
Y1 - 2005/11/1
SP - 2012
EP - 2018
KW - Galaxies: Clusters: General/ Galaxies: Distances and Redshifts
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AJ....130.2012W&db_key=AST&high=42a068d47531548
N2 - The Southern Abell Redshift Survey (SARS) contains 39 clusters of
galaxies with redshifts in the range 0.0degdeg,
alpha<5h,alpha>21h (while avoiding the
LMC and SMC), with |b|>40°. Cluster locations were chosen from
the Abell and Abell-Corwin-Olowin catalogs, while galaxy positions were
selected from the Automatic Plate Measuring Facility galaxy catalog with
extinction-corrected magnitudes in the range 15<=bJ<19.
SARS used the Las Campanas 2.5 m du Pont telescope, observing either 65
or 128 objects concurrently over a 1.5 deg2 field. New
redshifts for 3440 galaxies are reported in the fields of these 39
clusters of galaxies.
ER -
TY - Journal
T1 - Two Degree Field Galaxy Redshift Survey and Sloan Digital Sky Survey Galaxy Group Density Profiles
A1 - Díaz, Eugenia
A1 - Zandivarez, Ariel
A1 - Merchán, Manuel E.
A1 - Muriel, Hernán
JO - Astrophysical Journal
VL - 629
Y1 - 2005/8/1
SP - 158
EP - 171
KW - Galaxies: Clusters: General/ Galaxies: Statistics/ Methods: Data Analysis/ Methods: n-Body Simulations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...629..158D&db_key=AST&high=42a068d47531548
N2 - We have analyzed the distribution of galaxies in groups identified in
the largest redshift surveys available at present: the final release of
the 2dF Galaxy Redshift Survey and the first release of the Sloan
Digital Sky Survey. Our work comprises the study of the galaxy density
profiles and the fraction of galaxies per spectral type as a function of
the groupcentric distance. We have calculated the projected galaxy
density profiles of galaxy groups using composite samples in order to
increase the statistical significance of the results. Special care has
been taken in order to avoid possible biases in the group identification
and the construction of the projected galaxy density profile estimator.
The results show that the projected galaxy density profiles obtained for
both redshift surveys are in agreement with a projected Navarro, Frenk,
and White prediction in the range 0.15200<1,
whereas a good fit for the measured profiles in the whole range of
r/r200 is given by a projected King profile. We have adopted
a generalized King profile to fit the measured projected density
profiles per spectral type. In order to infer the three-dimensional
galaxy density profiles, we deproject the two-dimensional density
profiles using a deprojection method similar to that developed by Allen
and Fabian. From two-dimensional and three-dimensional galaxy density
profiles, we have estimated the corresponding galaxy fractions per
spectral type. The two-dimensional fraction of galaxies computed using
the projected profiles shows a similar segregation of galaxy spectral
types as that obtained by Domínguez and coworkers for groups in
the early data release of the 2dF Galaxy Redshift Survey. As expected,
the trends obtained for the three-dimensional galaxy fractions show
steeper slopes than those observed in the two-dimensional fractions.
ER -
TY - Journal
T1 - A Survey of N IV and O IV Features near 3400 Å in O2-O5 Spectra
A1 - Morrell, Nidia I.
A1 - Walborn, Nolan R.
A1 - Arias, Julia I.
JO - Publications of the Astronomical Society of the Pacific
VL - 117
Y1 - 2005/7/1
SP - 699
EP - 705
KW - Stars: Abundances/ Stars: Early-Type/ Stars: Evolution/ Stars: Fundamental Parameters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005PASP..117..699M&db_key=AST&high=42a068d47531548
N2 - We have conducted a survey of little-known N IV and O IV multiplets near
3400 Å in an extensive sample of well-classified, very early
O-type spectra. The initial motivation was to search for additional
useful classification criteria for these types, but an unexpected result
is the high sensitivity of these features to evolutionary CNO
processing. We have found a useful discriminant between O2 and later
types in the relative strengths of the O IV multiplets, one of which is
subject to selective emission in the hottest spectra; the overall
strengths of these lines also decrease between spectral types O4 and O5.
More remarkable, however, are the variations in the N/O ratios among
both individual stars and clusters. For instance, several O4 If+ spectra
have very large ratios, while main-sequence stars in the Carina Nebula
generally have smaller values than others of the same spectral types in
other regions. These effects correspond to different degrees of mixing
of processed material as a function of evolutionary age and initial
rotational velocities; the second effect provides significant further
evidence that very massive stars mix while still on the main sequence.
Thus, further analysis of these features will likely provide valuable
diagnostics of important evolutionary parameters.
ER -
TY - Journal
T1 - Absolute Parameters for Eight Eclipsing Binaries in the Large Magellanic Cloud: The Mass-Luminosity Relation
A1 - González, Jorge Federico
A1 - Ostrov, Pablo
A1 - Morrell, Nidia
A1 - Minniti, Dante
JO - Astrophysical Journal
VL - 624
Y1 - 2005/5/1
SP - 946
EP - 956
KW - Stars: Binaries: Eclipsing/ Galaxies: Magellanic Clouds/ Stars: Early-Type/ Stars: Fundamental Parameters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...624..946G&db_key=AST&high=42a068d47531548
N2 - A simultaneous light and radial velocity analysis of eight Large
Magellanic Cloud (LMC) eclipsing binaries is presented. Combining
spectroscopic observations obtained with UVES at the ESO Very Large
Telescope and light curves available from the MACHO and OGLE databases,
accurate masses and radii for the binary components, along with their
spectral types and luminosities, are derived. These determinations allow
us to construct the first mass-luminosity relation for late O and early
B type stars in the LMC. This mass-luminosity relation looks very
similar to that of the Milky Way, in spite of the different
metallicities. The good agreement achieved in the comparison with recent
theoretical isochrones is encouraging regarding the reliability of star
models up to 20 Msolar.
Based on observations obtained at the European Southern Observatory,
Paranal, with VLT UT2 (Kueyen); ESO programs 68.D-0328(A) and
70.D-0191(A).
ER -
TY - Journal
T1 - A Simple Method to Compensate Softening Effects in N-Body Simulations of Spherical Stellar Systems
A1 - Muzzio, J. C.
JO - Revista Mexicana de Astronomia y Astrofisica
VL - 41
Y1 - 2005/4/1
SP - 41
EP - 44
KW - Galaxies: Spherical/ Globular Clusters/ Methods: N-Body
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005RMxAA..41...41M&db_key=AST&high=42a068d47531548
N2 - Simulations of stellar systems involve, first, creating a model and,
subsequently, following its evolution through numerical integration of
the equations of motion. The models can be generated from theoretical
distributions obtained from the Newtonian potential, but the integration
demands resorting to softened potentials in order to reduce relaxation
effects. Usually, the difference between both potentials causes only
negligible alterations in the model, but in some cases (e.g., cuspy
distributions) it can substantially alter it. Here we present a
model-independent simple method to correct this problem in simulations
of spherical stellar systems.
ER -
TY - Journal
T1 - Spatial Structure of Regular and Chaotic Orbits in A Self-Consistent Triaxial Stellar System
A1 - Muzzio, J. C.
A1 - Carpintero, D. D.
A1 - Wachlin, F. C.
JO - Celestial Mechanics and Dynamical Astronomy
VL - 91
Y1 - 2005/1/1
SP - 173
EP - 190
KW - triaxial stellar systems/ stellar orbits/ chaotic motion
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005CeMDA..91..173M&db_key=AST&high=42a068d47531548
N2 - We created a triaxial stellar system through the cold dissipationless
collapse of 100,000 particles whose evolution was followed with a
multipolar code. Once an equilibrium system had been obtained, the
multipolar expansion was freezed and smoothed in order to get a
stationary smooth potential. The resulting model was self-consistent and
the orbits and Lyapunov exponents could then be computed for a randomly
selected sample of 3472 of the bodies that make up the system. More than
half of the orbits (52.7 % ) turned out to be chaotic. Regular orbits
were then classified using the frequency analysis automatic code of
Carpintero and Aguilar (1998, MNRAS 298(1), 1 21). We present plots of
the distributions of the different kinds of orbits projected on the
symmetry planes of the system. We distinguish chaotic orbits with only
one non-zero Lyapunov exponent from those with two non-zero exponents
and show that their spatial distributions differ, that of the former
being more similar to the one of the regular orbits. Most of the regular
orbits are boxes and boxlets, but the minor axis tubes play an important
role filling in the wasp waists of the boxes and helping to give a
lentil shape to the system. We see no problem in building stable
triaxial models with substantial amounts of chaotic orbits; the
difficulties found by other authors may be due not to a physical cause
but to a limitation of Schwarzschild's method.
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=42a068d47531548
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 - A CNO Dichotomy among O2 Giant Spectra in the Magellanic Clouds
A1 - Walborn, Nolan R.
A1 - Morrell, Nidia I.
A1 - Howarth, Ian D.
A1 - Crowther, Paul A.
A1 - Lennon, Daniel J.
A1 - Massey, Philip
A1 - Arias, Julia I.
JO - Astrophysical Journal
VL - 608
Y1 - 2004/6/1
SP - 1028
EP - 1038
KW - Galaxies: Magellanic Clouds/ Stars: Abundances/ Stars: Early-Type/ Stars: Evolution/ Stars: Fundamental Parameters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...608.1028W&db_key=AST&high=42a068d47531548
N2 - From a survey of the 3400 Å region in the earliest O-type spectra,
we have found that two of the four O2 giants observed in the Large
Magellanic Cloud have O IV lines there that are stronger than the N IV
lines, while the other two have the opposite. A Small Magellanic Cloud
counterpart also has N IV stronger than O IV. Inspection of the blue
spectra of these stars shows that the former pair have weaker N lines in
all ionization states (III, IV, and V) present as well as lines of C IV
lambda4658, while the latter three have stronger N lines and greater
He/H. Space ultraviolet observations of two of the N-strong stars show N
V wind profiles substantially stronger than those of C IV, while in the
N-weak stars the C IV features are equal to or stronger than the N V.
The N-strong stars are now reclassified as ON2 III(f*), newly defining
that category. These characteristics strongly suggest a larger fraction
of processed material in the atmospheres of the ON2 stars, which we
confirm by modeling the optical spectra. In the context of current
models, it is in turn implied that the ON2 stars are in a more advanced
evolutionary state than the others, and/or that they had higher initial
rotational velocities. The recent formulation of the effects of rotation
on massive stellar evolution introduces an additional fundamental
parameter, which the CNO abundances are in principle able to constrain.
We present some illustrative comparisons with current Geneva
evolutionary models for rotating massive stars. It is possible that
these very hot, nitrogen-rich objects are products of homogeneous
evolution. Our results will provide motivation for further physical
modeling of the atmospheres and evolutionary histories of the most
massive hot stars.
ER -
TY - Journal
T1 - Properties of groups of galaxies in the vicinity of massive clusters
A1 - Ragone, C. J.
A1 - Merchán, M.
A1 - Muriel, H.
A1 - Zandivarez, A.
JO - Monthly Notices of the Royal Astronomical Society
VL - 350
Y1 - 2004/5/1
SP - 983
EP - 988
KW - galaxies: clusters: general
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.350..983R&db_key=AST&high=42a068d47531548
N2 - This work analyses the properties of groups of galaxies in the vicinity
of clusters. On the basis of a very large public Virgo Consortium
Simulation, we identified systems of galaxies in a wide range of masses.
Systems with masses greater than Mcut= 4 ×
1014 Msolarh-1 are considered `hosts',
whereas smaller systems are taken as groups. Our results show that group
properties are affected by the proximity of massive hosts. Physical
properties such as velocity dispersion, internal energy (E) and virial
radius, show an increment, whereas the mean density decreases as the
host-group distance decreases. By analysing groups with different
properties, we find that the low mass and the weakly bound (E > 0)
subsamples are strongly affected by the presence of the host; on the
other hand, massive groups and groups with E < 0 do not show
dependence on the host-group distance. Using a sample of groups
identified in the final version of the 2dF Galaxy Redshift Survey, we
find a very similar velocity dispersion behaviour in the observational
data compared to results in the simulation. We also study the dependence
of the group velocity dispersion on the host masses in both observations
and simulation, and we find that the larger the host mass, the higher
the effect on its vicinity.
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=42a068d47531548
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 - Astronomical Site Testing in Northwest of Argentina
A1 - Recabarren, Pablo
A1 - Recabarren, Pablo
A1 - Mosconi, Mirta
A1 - Muriel, Hernán
A1 - Muriel, Hernán
A1 - Lambas, Diego García
A1 - Lambas, Diego García
A1 - Sarazin, Marc
A1 - Giovanelli, Riccardo
JO - Astrophysics and Space Science
VL - 290
Y1 - 2004/4/1
SP - 409
EP - 413
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..409R&db_key=AST&high=42a068d47531548
N2 - We present the preliminary results of the astronomical site testing,
which the group IATE of the OAC is developing in northwest of Argentine
in collaboration with ESO and the Department of Astronomy of Cornell
University.
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=42a068d47531548
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 - XMM-Newton X-ray observations of the Carina nebula
A1 - Albacete Colombo, J. F.
A1 - Méndez, M.
A1 - Morrell, N. I.
JO - Monthly Notices of the Royal Astronomical Society
VL - 346
Y1 - 2003/12/1
SP - 704
EP - 718
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.346..704C&db_key=AST&high=42a068d47531548
N2 - We use new XMM-Newton observations to perform a detailed X-ray analysis
of the Carina nebula region in the 0.3-12 keV energy range. Our source
detection yields 80 discrete X-ray sources, from which about 20 per cent
seem not to have optical counterparts. To get an idea of the energy
spectrum of these sources, we construct an X-ray colour-colour diagram
using the energy bands 0.3-2, 2-4.5 and 4.5-12 keV. We analyse the
spectra of the most intense X-ray sources associated with early-type
stars, including the luminous blue variable eta Carina and WR25. We
show that the X-ray emission from these sources is well fitted by
multitemperature model spectra. We detect surprisingly intense X-ray
emission at energies above 4 keV for some of the observed early-type
stars, especially from CPD-59 2629 (Tr16-22) which presents particularly
hard X-ray emission. We detect intense soft X-ray emission, below <2
keV, in HDE 303311, which presents an X-ray excess of about 100 times
higher than has been observed in other O5V stars. We use these data to
construct the Lx/Lbol relation for the 0.3-12 and
3.0-12 keV energy ranges, for all the observed O-type stars, plus eta
Carina and WR25. Most of the bright stars seem to agree with low
metallicity spectral models. The Lx/Lbol ratio for
O-type stars in the 0.3-12 keV range is well fitted by a constant
~6.07.54.8× 10-7, in fair
agreement with the canonical expression Lx/Lbol~ 2
× 10-7 formerly estimated for the 0.3-2.4 keV energy
band. In contrast, the Lx/Lbol relation for the
3.0-12 keV range presents a strong deviation from the canonical
relation, with a high dispersion of about four orders of magnitude. We
also detect intrinsic X-ray time variability in seven sources, over the
time-scale of about 50 h covered by the observations. This includes an
X-ray flare of about 2-h duration detected in DETWC Tr16
J104429.2-594143, a source probably not physically associated with the
Carina nebula. We discuss the different underlying physical mechanisms
that can be responsible for the X-ray emission from early-type stars.
ER -
TY - Journal
T1 - An asymptotic-giant-branch star in the progenitor system of a type Ia supernova
A1 - Hamuy, Mario
A1 - Phillips, M. M.
A1 - Suntzeff, Nicholas B.
A1 - Maza, José
A1 - González, L. E.
A1 - Roth, Miguel
A1 - Krisciunas, Kevin
A1 - Morrell, Nidia
A1 - Green, E. M.
A1 - Persson, S. E.
A1 - McCarthy, P. J.
JO - Nature
VL - 424
Y1 - 2003/8/1
SP - 651
EP - 654
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003Natur.424..651H&db_key=AST&high=42a068d47531548
N2 - Stars that explode as supernovae come in two main classes. A type Ia
supernova is recognized by the absence of hydrogen and the presence of
elements such as silicon and sulphur in its spectrum; this class of
supernova is thought to produce the majority of iron-peak elements in
the Universe. They are also used as precise `standard candles' to
measure the distances to galaxies. While there is general agreement that
a type Ia supernova is produced by an exploding white dwarf star, no
progenitor system has ever been directly observed. Significant effort
has gone into searching for circumstellar material to help discriminate
between the possible kinds of progenitor systems, but no such material
has hitherto been found associated with a type Ia supernova. Here we
report the presence of strong hydrogen emission associated with the type
Ia supernova SN2002ic, indicating the presence of large amounts of
circumstellar material. We infer from this that the progenitor system
contained a massive asymptotic-giant-branch star that lost several solar
masses of hydrogen-rich gas before the supernova explosion.
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=42a068d47531548
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 - 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=42a068d47531548
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 - Galaxy groups in the 2dF Galaxy Redshift Survey: a compactness analysis of groups
A1 - Zandivarez, A.
A1 - Domínguez, M. J. L.
A1 - Ragone, C. J.
A1 - Muriel, H.
A1 - Martínez, H. J.
JO - Monthly Notices of the Royal Astronomical Society
VL - 340
Y1 - 2003/4/1
SP - 1400
EP - 1408
KW - galaxies: clusters: general/ galaxies: statistics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.340.1400Z&db_key=AST&high=42a068d47531548
N2 - A comprehensive study on compactness has been carried out on the 2dF
Galaxy Group Catalogue constructed by Merchán and Zandivarez. The
compactness indices defined in this work take into account different
geometrical constraints in order to explore a wide range of
possibilities. Our results show that there is no clear distinction
between groups with high and low levels of compactness when considering
particular properties such as the radial velocity dispersion, the
relative fraction of galaxies per spectral type, and the luminosity
functions of their galaxy members. Studying the trend of the fraction of
galaxies per spectral type as a function of the dimensionless crossing
time, some signs of dynamical evolution are observed. From the
comparison with previous works on compactness, we realize that special
care should be taken for some compactness criteria definitions in order
to avoid possible biases in the identification.
ER -
TY - Journal
T1 - CCD photometric search for peculiar stars in open clusters. VI. NGC 1502, NGC 3105, Stock 16, NGC 6268, NGC 7235 and NGC 7510
A1 - Paunzen, E.
A1 - Netopil, M.
A1 - Iliev, I. Kh.
A1 - Maitzen, H. M.
A1 - Claret, A.
A1 - Pintado, O. I.
JO - Astronomy and Astrophysics
VL - 443
Y1 - 2005/11/1
SP - 157
EP - 162
KW - stars: chemically peculiar/ stars: early-type/ techniques: photometric/ Galaxy: globular clusters: general
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...443..157P&db_key=AST&high=42a068d47520318
N2 - In a sample of six young open clusters (NGC 1502, NGC 3105, Stock 16,
NGC 6268, NGC 7235, and NGC 7510) we investigated 1753 objects using the
narrow band, three filter Delta a photometric system resulting in the
detection of eleven bona-fide magnetic chemically peculiar (CP) stars
and five Be or metal-weak stars. The results for the distant cluster NGC
3105 is most important because of the still unknown influence of the
global metallicity gradient of the Milky Way. These findings confirm
that CP stars are present in open clusters of very young ages (log t
≥ 6.90) at galactocentric distances up to 11.4 kpc. For all
programme clusters the age, reddening, and distance modulus were derived
using the corresponding isochrones. Some additional variable stars
within Stock 16 could be identified by comparing different photometric
studies.
ER -
TY - Journal
T1 - On the incidence of chemically peculiar stars in the Large Magellanic Cloud
A1 - Paunzen, E.
A1 - Pintado, O. I.
A1 - Maitzen, H. M.
A1 - Claret, A.
JO - Monthly Notices of the Royal Astronomical Society
VL - 362
Y1 - 2005/9/1
SP - 1025
EP - 1030
KW - techniques: photometric/ stars: chemically peculiar/ stars: statistics/ Magellanic Clouds
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.362.1025P&db_key=AST&high=42a068d47520318
N2 - With the aim to corroborate the result of a search for chemically
peculiar stars in the Large Magellanic Cloud (LMC), we present
measurements obtained from CCD imaging of two fields, one containing a
young open cluster (NGC 1711). While for the latter field, including its
surrounding we obtain a contribution of 3 per cent of chemically
peculiar stars detectable by Deltaa photometry (i.e. the magnetic
objects of this group), the second field yields about half of this value
in good accordance with Maitzen et al.'s finding for NGC 1866, the
surrounding field of which has been found to exhibit a very low value of
such stars (0.3 per cent). Thus, we are faced with the fact that our
incipient impression about a substantially lower appearance of magnetic
chemically peculiar stars in the LMC as compared to the Galaxy continues
to be valid. Most of the photometrically identified peculiar stars (from
their historical origin denominated Ap stars) are located in the domain
of the B-type stars. However, this is a selection effect due to the
limiting magnitude of our observing conditions impeding the observation
of fainter main-sequence stars. In addition to objects showing up as
positive deviators in Deltaa photometry, we also discuss nine stars
which appear opposite the main line of normal stars, and hence are
negative deviators. For most of them, the interpretation as emission
stars of B-type seems to be appropriate. The statistically relevant
number of observations obtained so far in the LMC supports the view that
the formation of magnetic peculiar stars has occurred there at a
significantly lower rate.
ER -
TY - Journal
T1 - Integrated spectral analysis of 18 concentrated star clusters in the Small Magellanic Cloud
A1 - Piatti, A. E.
A1 - Santos, J. F. C., Jr.
A1 - Clariá, J. J.
A1 - Bica, E.
A1 - Ahumada, A. V.
A1 - Parisi, M. C.
JO - Astronomy and Astrophysics
VL - 440
Y1 - 2005/9/1
SP - 111
EP - 120
KW - galaxies: star clusters/ techniques: spectroscopic/ Magellanic Clouds
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...440..111P&db_key=AST&high=42a068d47520318
N2 - We present in this study flux-calibrated integrated spectra in the range
(3600-6800) Å for 18 concentrated SMC clusters. Cluster reddening
values were estimated by interpolation between the extinction maps of
Burstein & Heiles (1982, AJ, 87, 1165) and Schlegel et al. (1998,
ApJ, 500, 525). The cluster parameters were derived from the template
matching procedure by comparing the line strengths and continuum
distribution of the cluster spectra with those of template cluster
spectra with known parameters and from the equivalent width (EW) method.
In this case, new calibrations were used together with diagnostic
diagrams involving the sum of EWs of selected spectral lines. A very
good agreement between ages derived from both methods was found. The
final cluster ages obtained from the weighted average of values taken
from the literature and the present measured ones range from 15 Mr (e.g.
L 51) to 7 Gyr (K 3). Metal abundances have been derived for only 5
clusters from the present sample, while metallicity values directly
averaged from published values for other 4 clusters have been adopted.
Combining the present cluster sample with 19 additional SMC clusters
whose ages and metal abundances were put onto a homogeneous scale, we
analyse the age and metallicity distributions in order to explore the
SMC star formation history and its spatial extent. By considering the
distances of the clusters from the SMC centre instead of their
projections onto the right ascension and declination axes, the present
age-position relation suggests that the SMC inner disk could have been
related to a cluster formation episode which reached the peak ~2.5 Gyr
ago. Evidence for an age gradient in the inner SMC disk is also
presented.
ER -
TY - Journal
T1 - Tracing the formation history of intermediate-age star clusters in the Small Magellanic Cloud
A1 - Piatti, Andrés E.
A1 - Sarajedini, Ata
A1 - Geisler, Doug
A1 - Seguel, Juan
A1 - Clark, David
JO - Monthly Notices of the Royal Astronomical Society
VL - 358
Y1 - 2005/4/1
SP - 1215
EP - 1230
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.358.1215P&db_key=AST&high=42a068d47520318
N2 - Colour-magnitude diagrams (CMDs) are presented for the first time for 10
star clusters projected on to 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 turnoff
(MSTO), and metallicities from the red giant branch (RGB) locus. The
clusters all have ages in the range 1.5-4 Gyr and metallicities between
-1.3 < [Fe/H] < -0.6, with respective errors of ~0.5 Gyr and 0.3
dex. This increases substantially the sample of intermediate-age
clusters in the SMC with well-derived parameters. We combine our results
with those for other clusters in the literature to derive as large and
homogeneous a data base as possible (totalling 26 clusters) in order to
study global effects. We find evidence for two peaks in the age
distribution of SMC clusters, at ~6.5 and 2.5 Gyr, in good agreement
with previous hints involving smaller samples. The most recent peak
occurs at a time that corresponds to a very close encounter between the
Large Magellanic Cloud (LMC) and the SMC according to the recent
dynamical models of Bekki et al. that they used to explain the
enhancement of LMC clusters with this age. It appears cluster formation
may have been similarly stimulated in the SMC by this encounter as well.
We also find very good agreement between cluster ages and metallicities
and the prediction from a bursting model from Pagel and
Tautvaisiene with a burst that occurred 3 Gyr ago. These two
lines of evidence together favour a bursting cluster formation history
as opposed to a continuous one for the SMC.
ER -
TY - Journal
T1 - A CCD BVI Photometric Study of the Young, Highly Reddened Open Cluster NGC 6318
A1 - Piatti, Andrés E.
A1 - Clariá, Juan J.
A1 - Ahumada, Andrea V.
JO - Publications of the Astronomical Society of the Pacific
VL - 117
Y1 - 2005/1/1
SP - 22
EP - 31
KW - Galaxy: Open Clusters and Associations: General/ open clusters and associations: individual (NGC 6318)/ Techniques: Photometric
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005PASP..117...22P&db_key=AST&high=42a068d47520318
N2 - We present CCD BVI photometry for the southern open cluster NGC 6318.
The sample consists of 9876 stars measured in an area of
13.6m×13.6m, extending down to V~21.5 mag. Star counts
carried out within and outside the cluster region allowed us to estimate
the cluster angular radius as ~8'. The comparison of the cluster
color-magnitude diagrams with isochrones of the Geneva group yields
E(B-V)=1.20+/-0.05, E(V-I)=1.55+/-0.10, and V-MV=15.45+/-0.35
for logt=8.20 (t=160 Myr) and Z=0.020. NGC 6318 is then located at
2.1+/-0.5 kpc from the Sun and 30 pc below the Galactic plane. Using the
WEBDA open cluster database, we examined the structure of the Galactic
disk along the line of sight of NGC 6318. Among the known clusters in
this direction, HM 1 and BH 222 are the farthest ones, while those
located between 1 and 2 kpc of the Sun appear to be more absorbed than
those expected to follow a quasi-linear extinction law.
ER -
TY - Journal
T1 - Ages and metallicities of star clusters: New calibrations and diagnostic diagrams from visible integrated spectra
A1 - Santos, J. F. C., Jr.
A1 - Piatti, A. E.
JO - Astronomy and Astrophysics
VL - 428
Y1 - 2004/12/1
SP - 79
EP - 88
KW - galaxies: star clusters/ stars: fundamental parameters/ techniques: spectroscopic
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...428...79S&db_key=AST&high=42a068d47520318
N2 - We present homogeneous scales of ages and metallicities for star
clusters from very young objects, through intermediate-age ones up to
the oldest known clusters. All the selected clusters have integrated
spectra in the visible range, as well as reliable determinations of
their ages and metallicities. From these spectra equivalent widths (EWs)
of K Ca II, G band (CH) and Mg I metallic, and Hdelta, Hgamma and
Hbeta Balmer lines have been measured homogeneously. The analysis of
these EWs shows that the EW sums of the metallic and Balmer H lines,
separately, are good indicators of cluster age for objects younger than
10 Gyr, and that the former is also sensitive to cluster metallicity for
ages greater than 10 Gyr. We propose an iterative procedure for
estimating cluster ages by employing two new diagnostic diagrams and age
calibrations based on the above EW sums. For clusters older than 10 Gyr,
we also provide a calibration to derive their overall metal contents.
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=42a068d47520318
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=42a068d47520318
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=42a068d47520318
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 - New variable stars in open clusters. I. Methods and results for 20 open clusters
A1 - Paunzen, E.
A1 - Zwintz, K.
A1 - Maitzen, H. M.
A1 - Pintado, O. I.
A1 - Rode-Paunzen, M.
JO - Astronomy and Astrophysics
VL - 418
Y1 - 2004/4/1
SP - 99
EP - 102
KW - Galaxy: open clusters and associations: general/ stars: variables: general
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...418...99P&db_key=AST&high=42a068d47520318
N2 - We present high precision CCD photometry of 1791 objects in 20 open
clusters with an age of 10 Myr to 1 Gyr. These observations were
performed within the Delta a photometric system which is primarily
used to detect chemically peculiar stars of the upper main sequence.
Time bases range from 30 min up to 60 days with data from several
nights. We describe the time series analysis reaching a detection limit
of down to 0.006 mag for apparent variability. In total, we have
detected 35 variable objects of which four are not members of their
corresponding clusters. The variables cover the entire
Hertzsprung-Russell diagram, hence they are interesting targets for
follow-up observations.
Based on observations obtained at Complejo Astronómico el
Leoncito (CASLEO), operated under the agreement between the Consejo
Nacional de Investigaciones Científicas y Técnicas de la
República Argentina and the National Universities of La Plata,
Córdoba y San Juan; ESO-La Silla and UTSO-Las Campanas.
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=42a068d47520318
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=42a068d47520318
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 - 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=42a068d47520318
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 - 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=42a068d47520318
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 - 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=42a068d47520318
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 - Ages and metallicities of eight star clusters and their surrounding fields in the inner disc of the Large Magellanic Cloud
A1 - Geisler, Doug
A1 - Piatti, Andrés E.
A1 - Bica, Eduardo
A1 - Clariá, Juan J.
JO - Monthly Notices of the Royal Astronomical Society
VL - 341
Y1 - 2003/5/1
SP - 771
EP - 784
KW - techniques: photometric/ Magellanic Clouds/ galaxies: star clusters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.341..771G&db_key=AST&high=42a068d47520318
N2 - We present Washington system colour-magnitude diagrams for 8 star
clusters and their surrounding fields which, with one exception, lie
within the inner parts of the Large Magellanic Cloud (LMC) disc. Careful
attention is paid to separating out the cluster and field star
distributions. Ages and metallicities are then determined in a
consistent manner for both populations in two different ways. We first
compare the colour-magnitude diagrams (CMDs) with new theoretical
isochrones in the Washington system. We also derive ages using the
magnitude difference between the red clump and the turnoff, and derive
metallicities by comparing the giant branches to standard calibrating
clusters. For this latter metallicity derivation, we present
age-dependent metallicity corrections for intermediate age clusters
(IACs) based on the new isochrones. The two methods for both age and
metallicity determination are in good agreement with each other. All
clusters are found to be IACs (1-3 Gyr), with [Fe/H] from -0.4 to -0.9.
We find that the stellar population of each star cluster is generally
quite similar to that of the field where it is embedded, sharing its
mean age and metallicity. Combining the present sample with a revision
of that of Bica et al. studied similarly, we find that our metallicities
for IACs are intermediate in metallicity to those for clusters of
similar age studied by Olszewski et al. and by Beasley, Hoyle &
Sharples. A combined age-metallicity relation is presented which shows
that LMC clusters formed between 1-3 Gyr ago with a mean metallicity
(-0.5 dex) and metallicity spread (0.23 dex) independent of age. Good
agreement is found with the bursting model of Pagel & Tautvaisiene.
No evidence for a metallicity gradient is found.
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=42a068d47520318
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 - On the relationship between the mercury-manganese stars and the metallic-lined stars
A1 - Adelman, Saul J.
A1 - Adelman, A. S.
A1 - Pintado, O. I.
JO - Astronomy and Astrophysics
VL - 397
Y1 - 2003/1/1
SP - 267
EP - 273
KW - stars: chemically peculiar/ stars: Hertzsprung-Russell (HR) diagram and C-/ diagrams/ methods: statistical
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...397..267A&db_key=AST&high=42a068d47520318
N2 - An HR diagram indicating the positions of the HgMn and the Am stars
analyzed by the senior author and his collaborators shows that the
coolest HgMn stars and the hottest Am stars are found on the same
stellar evolutionary tracks and hence the former must evolve into the
later. The explanation of the dividing line between these two types of
nonmagnetic chemically peculiar stars where the Hg abundances suddenly
change their degree of overabundance is a major test of the theories
which try to explain the anomalous abundances of such stars. Some other
important relationships are found which can also serve as tests of
theories which purport to explain the properties of these stars.
ER -
TY - Journal
T1 - Cosmic-Ray Acceleration at the Forward Shock in Tycho's Supernova Remnant: Evidence from Chandra X-Ray Observations
A1 - Warren, Jessica S.
A1 - Hughes, John P.
A1 - Badenes, Carles
A1 - Ghavamian, Parviz
A1 - McKee, Christopher F.
A1 - Moffett, David
A1 - Plucinsky, Paul P.
A1 - Rakowski, Cara
A1 - Reynoso, Estela
A1 - Slane, Patrick
JO - Astrophysical Journal
VL - 634
Y1 - 2005/11/1
SP - 376
EP - 389
KW - ISM: individual (Tycho)/ Stars: Supernovae: General/ ISM: Supernova Remnants/ X-Rays: ISM
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...634..376W&db_key=AST&high=42a068d47524087
N2 - We present evidence for cosmic-ray acceleration at the forward shock in
Tycho's supernova remnant (SNR) from three X-ray observables: (1) the
proximity of the contact discontinuity to the forward shock, or blast
wave, (2) the morphology of the emission from the rim of Tycho, and (3)
the spectral nature of the rim emission. We determine the locations of
the blast wave (BW), contact discontinuity (CD), and reverse shock (RS)
around the rim of Tycho's supernova remnant using a principal component
analysis and other methods applied to new Chandra data. The
azimuthal-angle-averaged radius of the BW is 251". For the CD and RS we
find average radii of 241" and 183", respectively. Taking account of
projection effects, we find ratios of 1:0.93:0.70 (BW:CD:RS). We show
these values to be inconsistent with adiabatic hydrodynamic models of
SNR evolution. The CD:BW ratio can be explained if cosmic-ray
acceleration of ions is occurring at the forward shock. The RS:BW ratio,
as well as the strong Fe Kalpha emission from the Tycho ejecta, imply
that the RS is not accelerating cosmic rays. We also extract radial
profiles from ~34% of the rim of Tycho and compare them to models of
surface brightness profiles behind the BW for a purely thermal plasma
with an adiabatic shock. The observed morphology of the rim is much more
strongly peaked than predicted by the model, indicating that such
thermal emission is implausible here. Spectral analysis also implies
that the rim emission is nonthermal in nature, lending further support
to the idea that Tycho's forward shock is accelerating cosmic rays.
ER -
TY - Journal
T1 - Chemical evolution in the environment of intermediate mass young stellar objects
A1 - Fuente, A.
A1 - Rizzo, J. R.
A1 - Caselli, P.
A1 - Bachiller, R.
A1 - Henkel, C.
JO - Astronomy and Astrophysics
VL - 433
Y1 - 2005/4/1
SP - 535
EP - 552
KW - stars: formation/ stars: pre-main sequence/ stars: individual: LkHalpha 234/ ISM: abundances/ ISM: clouds/ ISM: individual objects: NGC 7129
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...433..535F&db_key=AST&high=42a068d47524087
N2 - We have carried out a molecular survey of the Class 0 IM protostar NGC
7129 - FIRS 2 (hereafter FIRS 2) and the Herbig Be star LkHalpha 234
with the aim of studying the chemical evolution of the envelopes of
intermediate-mass (IM) young stellar objects (YSOs). The two objects
have similar luminosities (~500 L_⊙) and are located in the same
molecular cloud which minimizes the chemical differences due to
different stellar masses or initial cloud conditions. Moreover, since
they are located at the same distance, we have the same spatial
resolution in both objects. A total of 17 molecular species (including
rare isotopes) have been observed in both objects and the structure of
their envelopes and outflows has been determined with unprecedent
detail. Our results show that the protostellar envelopes are dispersed
and warmed up during the evolution of the YSO into a pre-main sequence
star. In fact, the envelope mass decreases by a factor >5 from FIRS 2
to LkHalpha 234, while the kinetic temperature increases from ~13 K to
28 K. On the other hand, there is no molecular outflow associated with
LkHalpha 234. The molecular outflow seems to stop before the star
becomes visible. These physical changes strongly affect the chemistry of
their envelopes. The N2H+ and NH3 abundances seem to be quite
similar in the two objects. However, the H13CO+
abundance is a factor of ~3 lower in the densest part of FIRS 2 than in
LkHalpha 234, very likely because of depletion. In contrast, the SiO
abundance is larger by a factor of ~100 in FIRS 2 than in LkHalpha
234. CS presents complex behavior since its emission arises in different
envelope components (outflow, cold envelope, hot core) and could also
suffer from depletion. The CH3OH and H2CO column densities are very
similar in FIRS 2 and LkHalpha 234 which implies that the
beam-averaged abundances are a factor >5 larger in LkHalpha 234
than in FIRS 2. The same is found for the PDR tracers CN and HCN which
have similar column densities in both objects. Finally, complex behavior
is found for the deuterated compounds. While the
DCO^+/H13CO+ ratio decreases by a factor of ~4
from FIRS 2 to LkHalpha 234, the D2CO/H2CO ratios is within a factor
1.5 in both objects. The detection of a warm CH3CN component with
Tk >63 K shows the existence of a hot core in FIRS 2. Thus
far, only a handful of hot cores have been detected in low and
intermediate mass stars. Based on our results in FIRS 2 and LkHalpha
234, we propose some abundance ratios that can be used as chemical
clocks for the envelopes of IM YSOs. The SiO/CS, CN/N2H^+, HCN/N2H^+,
DCO^+/HCO+ and D2CO/DCO+ ratios are good
diagnostics of the protostellar evolutionary stage.
Tables 1-3 are only available in electronic form at
http://www.edpsciences.org
ER -
TY - Journal
T1 - Photon-dominated Chemistry in the Nucleus of M82: Widespread HOC+ Emission in the Inner 650 Parsec Disk
A1 - Fuente, A.
A1 - García-Burillo, S.
A1 - Gerin, M.
A1 - Teyssier, D.
A1 - Usero, A.
A1 - Rizzo, J. R.
A1 - de Vicente, P.
JO - Astrophysical Journal
VL - 619
Y1 - 2005/2/1
SP - L155
EP - L158
KW - Galaxies: Individual: Messier Number: M82/ Galaxies: Nuclei/ Galaxies: Starburst/ ISM: Abundances/ ISM: Molecules/ Radio Lines: Galaxies
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...619L.155F&db_key=AST&high=42a068d47524087
N2 - The nucleus of M82 has been mapped in several 3 and 1 mm lines of CN,
HCN, C2H, c-C3H2,
CH3C2H, HC3N, and HOC+ using
the IRAM 30 m telescope. These species have been purposely selected as
good tracers of photon-dominated chemistry. We have measured
[CN]/[HCN]~5 in the inner 650 pc galaxy disk. Furthermore, we have
detected the HOC+ 1-->0 line with an intensity similar to
that of the H13CO+ 1-->0 line. This implies an
[HCO+]/[HOC+] ratio of ~40. These results
corroborate the existence of a giant photodissociation region (PDR) in
the nucleus of M82. In fact, the low [HCO+]/[HOC+]
ratio can only be explained if the nucleus of M82 is formed by small
(r<0.02-0.2 pc) and dense (n~a few times
104-105 cm-3) clouds immersed in an
intense UV field (G0~104 in units of the Habing
field). The detection of the hydrocarbons c-C3H2
and CH3C2H in the nucleus of M82 suggests that a
complex carbon chemistry is developing in this giant PDR.
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=42a068d47524087
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 - Shocked gas layers surrounding the WR nebula NGC 2359
A1 - Rizzo, J. R.
A1 - Martín-Pintado, J.
A1 - Desmurs, J.-F.
JO - Astronomy and Astrophysics
VL - 411
Y1 - 2003/12/1
SP - 465
EP - 475
KW - stars: individual: HD 56925/ stars: Wolf-Rayet/ stars: winds/ outflows/ ISM: bubbles\/ ISM: individual objects: NGC 2359/ ISM: kinematics and dynamics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...411..465R&db_key=AST&high=42a068d47524087
N2 - NGC 2359 is a Wolf-Rayet (W-R) nebula partially bound by a rather dense
and warm molecular cloud. We present the results derived from CO and
13CO fully sampled maps of the molecular material with
angular resolutions up to 12arcsec . We have detected three different
velocity components, and determined their spatial distribution and
physical properties. The kinematics, morphology, mass and density are
clearly stratified with respect to the W-R star. These features allow us
to learn about the recent evolutionary history of HD 56925, because the
multiple layers could be associated to several energetic events which
have acted upon the surrounding circumstellar medium. Hence, a careful
study of the different shockfronts contain clues in determining the
present and past interaction of this evolved massive star with its
surroundings. From the analysis of the mass-loss history in massive
stars like HD 56925, we suggest that the multiple layers of shocked
molecular gas are likely to be produced during the earlier LBV phase
and/or the actual W-R stage of HD 56925.
ER -
TY - Journal
T1 - Detection of Reactive Ions in the Ultracompact H II Regions Monoceros R2 and G29.96-0.02
A1 - Rizzo, J. R.
A1 - Fuente, A.
A1 - Rodríguez-Franco, A.
A1 - García-Burillo, S.
JO - Astrophysical Journal
VL - 597
Y1 - 2003/11/1
SP - L153
EP - L156
KW - ISM: H II Regions/ ISM: Individual: Alphanumeric: G29.96-0.02/ ISM: Individual: Name: Monoceros R2/ ISM: Molecules/ Stars: Early-Type/ Stars: Formation
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...597L.153R&db_key=AST&high=42a068d47524087
N2 - We report the first detection of the reactive ions CO+ and
HOC+ toward ultracompact (UC) H II regions, particularly in
Mon R2 and G29.96-0.02. We have observed two positions in Mon R2,
namely, the peak of the UC H II region and the surrounding high-density
molecular cloud. CO+ and HOC+ were detected at the
UC H II region but not at the molecular cloud, as expected if both ions
arise in the photodissociation region (PDR) surrounding the UC H II
region. The measured column densities are on the order of
1011 cm-2 in both sources, which yields a
strikingly low [HCO+]/[HOC+] abundance ratio of
460 in Mon R2. These values are similar to those found in some other
well-known PDRs, like NGC 7023 and the Orion bar. We briefly discuss the
chemical implications of these results.
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=42a068d47524087
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 - Feedback and metal enrichment in cosmological smoothed particle hydrodynamics simulations - I. A model for chemical enrichment
A1 - Scannapieco, C.
A1 - Tissera, P. B.
A1 - White, S. D. M.
A1 - Springel, V.
JO - Monthly Notices of the Royal Astronomical Society
VL - 364
Y1 - 2005/12/1
SP - 552
EP - 564
KW - methods: numerical/ galaxies: abundances/ galaxies: evolution/ galaxies: formation/ cosmology: theory
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.364..552S&db_key=AST&high=42a068d47531810
N2 - We discuss a model for treating chemical enrichment by Type II and Type
Ia supernova (SNII and SNIa) explosions in simulations of cosmological
structure formation. Our model includes metal-dependent radiative
cooling and star formation in dense collapsed gas clumps. Metals are
returned into the diffuse interstellar medium by star particles using a
local smoothed particle hydrodynamics (SPH) smoothing kernel. A variety
of chemical abundance patterns in enriched gas arise in our treatment
owing to the different yields and lifetimes of SNII and SNIa progenitor
stars. In the case of SNII chemical production, we adopt metal-dependent
yields. Because of the sensitive dependence of cooling rates on
metallicity, enrichment of galactic haloes with metals can in principle
significantly alter subsequent gas infall and the build-up of the
stellar components. Indeed, in simulations of isolated galaxies we find
that a consistent treatment of metal-dependent cooling produces 25 per
cent more stars outside the central region than simulations with a
primordial cooling function. In the highly enriched central regions, the
evolution of baryons is however not affected by metal cooling, because
here the gas is always dense enough to cool. A similar situation is
found in cosmological simulations because we include no strong feedback
processes which could spread metals over large distances and mix them
into unenriched diffuse gas. We demonstrate this explicitly with test
simulations which adopt suprasolar cooling functions leading to large
changes both in the stellar mass and in the metal distributions. We also
find that the impact of metallicity on the star formation histories of
galaxies may depend on their particular evolutionary history. Our
results hence emphasize the importance of feedback processes for
interpreting the cosmic metal enrichment.
ER -
TY - Journal
T1 - Fingerprints of the hierarchical building-up of the structure on the mass-metallicity relation
A1 - Tissera, Patricia B.
A1 - De Rossi, María E.
A1 - Scannapieco, Cecilia
JO - Monthly Notices of the Royal Astronomical Society
VL - 364
Y1 - 2005/11/1
SP - L38
EP - L41
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.364L..38T&db_key=AST&high=42a068d47531810
N2 - We study the mass-metallicity relation of galactic systems with stellar
masses larger than 109Msolarh-1 in
Lambda cold dark matter scenarios by using chemical hydrodynamical
simulations. We find that this relation arises naturally as a
consequence of the formation of the structure in a hierarchical
scenario. The hierarchical building-up of the structure determines a
characteristic stellar mass at Mc~
1010.2Msolarh-1 which exhibits
approximately solar metallicities from z~ 3 to z= 0. This characteristic
mass separates galactic systems into two groups with massive ones
forming most of their stars and metals at high redshift. We find
evolution in the zero point and slope of the mass-metallicity relation
driven mainly by the low-mass systems which exhibit the larger
variations in the chemical properties. Although stellar mass and
circular velocity are directly related, the correlation between circular
velocity and metallicity shows a larger evolution with redshift because
of the combination of chemical evolution and cosmology. The dispersion
found in both relations is a function of the stellar mass and reflects
the different dynamical history of evolution of the systems.
ER -
TY - Journal
T1 - Separation of Different Contributions to the Total X-ray Luminosity in Gamma-ray Loud Blazars
A1 - Fan, Jun-Hui
A1 - Romero, Gustavo E.
A1 - Wang, Yong-Xiang
A1 - Zhang, Jiang-Shui
JO - Chinese Journal of Astronony and Astrophysics
VL - 5
Y1 - 2005/10/1
SP - 457
EP - 462
KW - galaxies: active-galaxies/ jets/ X-rays: galaxies
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ChJAA...5..457F&db_key=AST&high=42a068d47531810
N2 - The relativistic beaming model has been successfully used to explain
many of the observational properties of active galactic nuclei. In this
model the total emission is formed by two components, one beamed, one
unbeamed. However, the exact contribution from each component in
unresolved sources is still not clear. In the radio band, the core and
extended emissions are clearly separated. We adopt the method proposed
by Kembhavi to separate the two contributions in the X-ray emissions in
a sample of 19 gamma-ray loud blazars. It is clearly shown that the
beamed emission dominates the X-ray flux and the unbeamed X-ray emission
is correlated with the extended radio emission of the considered
objects. We also find that the ratio of the beamed to the unbeamed X-ray
luminosity is correlated with the X-ray spectral index, an effect that
should be a consequence of the underlying X-ray emission mechanism.
ER -
TY - Journal
T1 - Hadronic High-Energy Gamma-Ray Emission from the Microquasar LS I +61 303
A1 - Romero, Gustavo E.
A1 - Christiansen, Hugo R.
A1 - Orellana, Mariana
JO - Astrophysical Journal
VL - 632
Y1 - 2005/10/1
SP - 1093
EP - 1098
KW - Gamma Rays: Observations/ Gamma Rays: Theory/ stars: individual (LS I +61 303)/ X-Rays: Binaries
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...632.1093R&db_key=AST&high=42a068d47531810
N2 - We present a hadronic model for gamma-ray production in the microquasar
LS I +61 303. The system is formed by a neutron star that accretes
matter from the dense and slow equatorial wind of the Be primary star.
We calculate the gamma-ray emission originating from pp interactions
between relativistic protons in the jet and cold protons from the wind.
After taking into account opacity effects on the gamma rays introduced
by the different photon fields, we present high-energy spectral
predictions that can be tested with the new-generation Cerenkov
telescope MAGIC.
ER -
TY - Journal
T1 - Polarization microvariability of BL Lacertae objects
A1 - Andruchow, I.
A1 - Romero, G. E.
A1 - Cellone, S. A.
JO - Astronomy and Astrophysics
VL - 442
Y1 - 2005/10/1
SP - 97
EP - 107
KW - galaxies: active/ galaxies: BL Lacertae objects: general/ polarization
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...442...97A&db_key=AST&high=42a068d47531810
N2 - We present the results of a systematic observational campaign designed
to search for microvariability in the optical polarization of BL Lac
objects. We observed a sample formed by 8 X-ray-selected and 10
radio-selected sources, looking for rapid changes in both the degree of
linear polarization and the corresponding polarization angle. The whole
campaign was carried out during the last three years, and most of the
objects were observed on at least two consecutive nights. The
statistical properties of both classes of BL Lac objects are
compared, and some general conclusions on the nature of the phenomenon
are drawn. In general, radio selected sources seem to display higher
duty cycles for polarimetric microvariability and, on average, they have
a stronger polarization.
ER -
TY - Journal
T1 - Gamma-ray and neutrino emission from misaligned microquasars
A1 - Romero, G. E.
A1 - Orellana, M.
JO - Astronomy and Astrophysics
VL - 439
Y1 - 2005/8/1
SP - 237
EP - 244
KW - X-ray: binaries/ gamma-rays: theory/ gamma-rays: observations/ neutrinos
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...439..237R&db_key=AST&high=42a068d47531810
N2 - Microquasars are accreting X-ray binary systems with non-thermal radio
jets. In some of these systems the jet is expected to be strongly
misaligned with the perpendicular to the orbital plane. If the donor
star is an early-type star, the jet could collide with the stellar wind
producing a standing shock between the compact object and the stellar
surface. Relativistic particles injected by the jet can be
re-accelerated and isotropized at the colliding region. If the jet has
hadronic content, TeV protons will diffuse into the inner, dense wind
leading to gamma-ray and neutrino production from interactions with the
matter of the wind. In the case of very powerful jets, the wind pressure
can be overbalanced and the jet might impact directly onto the stellar
surface. We present estimates of the gamma-ray and neutrino luminosities
for different sets of parameters in these scenarios and we briefly
discuss the effects of this radiation on the donor star and its
detectability with current instruments.
ER -
TY - Journal
T1 - The WEBT campaign to observe AO 0235+16 in the 2003-2004 observing season. Results from radio-to-optical monitoring and XMM-Newton observations
A1 - Raiteri, C. M.
A1 - Villata, M.
A1 - Ibrahimov, M. A.
A1 - Larionov, V. M.
A1 - Kadler, M.
A1 - Aller, H. D.
A1 - Aller, M. F.
A1 - Kovalev, Y. Y.
A1 - Lanteri, L.
A1 - Nilsson, K.
A1 - Papadakis, I. E.
A1 - Pursimo, T.
A1 - Romero, G. E.
A1 - Teräsranta, H.
A1 - Tornikoski, M.
A1 - Arkharov, A. A.
A1 - Barnaby, D.
A1 - Berdyugin, A.
A1 - Böttcher, M.
A1 - Byckling, K.
A1 - Carini, M. T.
A1 - Carosati, D.
A1 - Cellone, S. A.
A1 - Ciprini, S.
A1 - Combi, J. A.
A1 - Crapanzano, S.
A1 - Crowe, R.
A1 - di Paola, A.
A1 - Dolci, M.
A1 - Fuhrmann, L.
A1 - Gu, M.
A1 - Hagen-Thorn, V. A.
A1 - Hakala, P.
A1 - Impellizzeri, V.
A1 - Jorstad, S.
A1 - Kerp, J.
A1 - Kimeridze, G. N.
A1 - Kovalev, Yu. A.
A1 - Kraus, A.
A1 - Krichbaum, T. P.
A1 - Kurtanidze, O. M.
A1 - Lähteenmäki, A.
A1 - Lindfors, E.
A1 - Mingaliev, M. G.
A1 - Nesci, R.
A1 - Nikolashvili, M. G.
A1 - Ohlert, J.
A1 - Orio, M.
A1 - Ostorero, L.
A1 - Pasanen, M.
A1 - Pati, A.
A1 - Poteet, C.
A1 - Ros, E.
A1 - Ros, J. A.
A1 - Shastri, P.
A1 - Sigua, L. A.
A1 - Sillanpää, A.
A1 - Smith, N.
A1 - Takalo, L. O.
A1 - Tosti, G.
A1 - Vasileva, A.
A1 - Wagner, S. J.
A1 - Walters, R.
A1 - Webb, J. R.
A1 - Wills, W.
A1 - Witzel, A.
A1 - Xilouris, E.
JO - Astronomy and Astrophysics
VL - 438
Y1 - 2005/7/1
SP - 39
EP - 53
KW - galaxies: active/ BL Lacertae objects: general/ BL Lacertae objects: individual: AO 0235+16
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...438...39R&db_key=AST&high=42a068d47531810
N2 - A multiwavelength campaign to observe the BL Lac object AO
0235+16 (z=0.94) was set up by the Whole Earth Blazar
Telescope (WEBT) collaboration during the observing seasons 2003-2004
and 2004-2005, involving radio, near-IR and optical photometric
monitoring, VLBA monitoring, optical spectral monitoring, and three
pointings by the XMM-Newton satellite. Here we report on the results of
the first season, which involved the participation of 24 optical and
near-IR telescopes and 4 radio telescopes, as well as the first
XMM-Newton pointing, which occurred on January 18-19, 2004. Unpublished
data from previous epochs were also collected (from 5 optical-NIR and 3
radio telescopes), in order to fill the gap between the end of the
period presented in Raiteri et al. (2001) and the start of the WEBT
campaign. The contribution of the southern AGN, 2 arcsec distant from
the source, is taken into account. It is found to especially affect the
blue part of the optical spectrum when the source is faint. In the
optical and near-IR the source has been very active in the last 3 years,
although it has been rather faint most of the time, with noticeable
variations of more than a magnitude over a few days. In contrast, in the
radio bands it appears to have been ``quiescent'' since early
2000. The major radio (and optical) outburst predicted to peak around
February-March 2004 (with a six month uncertainty) has not occurred yet.
When comparing our results with the historical light curves, two
different behaviours seem to characterize the optical outbursts: only
the major events present a radio counterpart. The X-ray spectra obtained
by the three EPIC detectors are well fitted by a power law with
extra-absorption at z=0.524; the energy index in the 0.2-10 keV range is
well constrained: alpha=0.645 ± 0.028 and the 1 keV flux
density is 0.311 ± 0.008~mu Jy. The analysis of the X-ray light
curves reveals that no significant variations occurred during the
pointing. In contrast, simultaneous dense radio monitoring with the 100
m telescope at Effelsberg shows a ~2-3% flux decrease in 6-7 h, which,
if intrinsic, would imply a brightness temperature well above the
Compton limit and hence a lower limit to the Doppler factor delta
î«¢ 46. We construct the broad-band spectral energy distribution of
January 18-19, 2004 with simultaneous radio data from Effelsberg,
optical data from the Nordic Optical Telescope (NOT), optical-UV data
from the Optical Monitor onboard XMM-Newton, and X-ray data by the EPIC
instruments. Particular care is taken to correct data for extinction due
to both the Milky Way and the z=0.524 absorber. The resulting SED
suggests the existence of a bump in the UV spectral region.
ER -
TY - Journal
T1 - Microquasar Models for 3EG J1828+0142 and 3EG J1735-1500
A1 - Bosch-Ramon, V.
A1 - Paredes, J. M.
A1 - Romero, G. E.
A1 - Torres, D. F.
JO - Chinese Journal of Astronony and Astrophysics
VL - 5
Y1 - 2005/6/1
SP - 284
EP - 288
KW - X-rays: binaries/ Stars: winds/ outflows/ gamma-rays: observations/ gamma-rays: theory
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ChJAA...5S.284B&db_key=AST&high=42a068d47531810
N2 - Microquasars are promising candidates to emit high-energy gamma-rays.
Moreover, statistical studies show that variable EGRET sources at low
galactic latitudes could be associated with the inner spiral arms. The
variable nature and the location in the Galaxy of the high-mass
microquasars, concentrated in the galactic plane and within 55 degrees
from the galactic center, give to these objects the status of likely
counterparts of the variable low-latitude EGRET sources. We consider in
this work the two most variable EGRET sources at low-latitudes: 3EG
J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain
the EGRET data in consistency with the observations at lower energies
(from radio frequencies to soft gamma-rays) within the EGRET error box.
ER -
TY - Journal
T1 - Neutrinos from Microquasars
A1 - Torres, Diego F.
A1 - Romero, Gustavo E.
A1 - Mirabel, Felix
JO - Chinese Journal of Astronony and Astrophysics
VL - 5
Y1 - 2005/6/1
SP - 183
EP - 188
KW - X-rays: binaries/ Stars: winds/ outflows/ gamma-rays: observations/ gamma-rays: theory
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ChJAA...5S.183T&db_key=AST&high=42a068d47531810
N2 - The jets of microquasars with high-mass stellar companions are exposed
to the dense matter field of the stellar wind as well as to the photon
densities found in the surrounding medium. Photopion and proton-proton
interactions could then lead to copious production of neutrinos. In this
work, we analyze the hadronic microquasar model, particularly in what
concerns to the neutrino production. Limits to this kind of models using
data from AMANDA-II are established. New constraints are also imposed
upon specific microquasar models based on photopion processes. These are
very restrictive particularly for the case of SS433, a microquasar for
which the presence of accelerated hadrons has been already inferred from
iron X-ray line observations.
ER -
TY - Journal
T1 - Microquasars and Gamma-ray Sources
A1 - Romero, Gustavo E.
JO - Chinese Journal of Astronony and Astrophysics
VL - 5
Y1 - 2005/6/1
SP - 110
EP - 120
KW - X-rays: binaries/ radiation mechanisms: non-thermal/ gamma rays: observations/ gamma rays: theory
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ChJAA...5S.110R&db_key=AST&high=42a068d47531810
N2 - Microquasars are X-ray binary systems with non-thermal radio emission
originated in jet-like features. They are attractive sites for gamma-ray
production, since relativistic particles in the jet should traverse
locally strong both photon and matter fields. In this review we discuss
whether some of the unidentified gamma-ray sources detected by the EGRET
instrument of the Compton Gamma-Ray Observatory might be associated with
microquasars. Relevant models for gamma-ray emission in such binaries
are described and prospects for the detection of microquasars with
instruments of new generation are briefly evaluated.
ER -
TY - Journal
T1 - Probing the Precession of the Inner Accretion Disk in Cygnus X-1
A1 - Torres, Diego F.
A1 - Romero, Gustavo E.
A1 - Barcons, Xavier
A1 - Lu, Youjun
JO - Astrophysical Journal
VL - 626
Y1 - 2005/6/1
SP - 1015
EP - 1019
KW - X-Rays: Binaries/ X-Rays: Individual: Constellation Name: Cygnus X-1
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...626.1015T&db_key=AST&high=42a068d47531810
N2 - We show that changes in the orientation of the inner accretion disk of
Cyg X-1 affect the shape of the broad Fe Kalpha emission line emitted
from this object, in such a way that eV-level spectral resolution
observations (such as those that will be carried out by the Astro-E2
satellite) can be used to analyze the dynamics of the disk. We present
here a potential diagnostic tool supported by numerical simulations by
which a few observations of Cyg X-1, separated in time, can determine
whether its accretion disk actually precesses, and if so, determine its
period and precession angle. This approach could also be used for
similar studies in other microquasar systems.
ER -
TY - Journal
T1 - Status of the Connection between Unidentified Egret Sources and Supernova Remnants: The Case of Cta 1
A1 - Torres, Diego F.
A1 - Dame, Thomas M.
A1 - Romero, Gustavo E.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
SP - 393
EP - 398
KW - supernova remnants/ gamma rays: observations/ interstellar medium
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297..393T&db_key=AST&high=42a068d47531810
N2 - In this paper we briefly comment on the observational status of the
possible physical association between unidentified EGRET sources and
supernova remnants (SNRs) in our Galaxy. We draw upon recent results
presented in the review by Torres et al. (2003), concerning molecular
gas in the vicinity of all 19 SNRs found to be positionally coincident
with EGRET sources at low Galactic latitudes. In addition, we present
new results regarding the supernova remnant CTA 1. Our findings disfavor
the possibility of a physical connection with the nearby (in projection)
EGRET source. There remains possible, however, that the compact object
produced in the supernova explosion be related with the observed
gamma-ray flux.
ER -
TY - Journal
T1 - Gamma-Ray Emission from Be/X-ray Binaries
A1 - Orellana, M.
A1 - Romero, G. E.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
SP - 167
EP - 178
KW - X-ray binaries/ neutron stars/ gamma-rays
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297..167O&db_key=AST&high=42a068d47531810
N2 - Be/X-ray binaries are systems formed by a massive Be star and a
magnetized neutron star, usually in an eccentric orbit. The Be star has
strong equatorial winds occasionally forming a circumstellar disk. When
the neutron star intersects the disk the accretion rate dramatically
increases and a transient accretion disk can be formed around the
compact object. This disk can last longer than a single orbit in the
case of major outbursts. If the disk rotates faster than the neutron
star, the Cheng-Ruderman mechanism can produce a current of relativistic
protons that would impact onto the disk surface, producing gamma-rays
from neutral pion decays and initiating electromagnetic cascades inside
the disk. In this paper we present calculations of the evolution of the
disk parameters during both major and minor X-ray events, and we discuss
the generation of gamma-ray emission at different energies within a
variety of models that include both screened and unscreened disks.
ER -
TY - Journal
T1 - On the Nature of the Variable Gamma-Ray Sources at Low Galactic Latitudes
A1 - Bosch-Ramon, Valentí
A1 - Romero, Gustavo E.
A1 - Paredes, Josep M.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
SP - 119
EP - 129
KW - microquasars/ X-ray binaries/ jets/ gamma-rays
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297..119B&db_key=AST&high=42a068d47531810
N2 - Population studies of EGRET gamma-ray sources indicate that there is a
distinctive population of bright sources at low galactic latitudes. The
sources have a distribution consistent with that of young galactic
objects, with a concentration toward the inner spiral arms. There is a
subgroup that displays strong variability with timescales from days to
months. Following an earlier suggestion by Kaufman Bernadó et al.
(2002), we explore the possibility that these sources could be high-mass
microquasars. Detailed models for the gamma-ray emission that include
inverse Compton interactions of electrons in the relativistic jets and
photons from all local fields (stellar UV photons, synchrotron photons,
soft X-ray photons from the accretion disk, and hard X-ray photons from
a corona) are presented. We conclude that microquasars are excellent
candidates for the parent population of the subgroup of variable
low-latitude EGRET sources.
ER -
TY - Journal
T1 - Unidentified gamma-ray Sources off the Galactic Plane as Low-Mass Microquasars?
A1 - Grenier, I. A.
A1 - Bernadó, M. M. Kaufman
A1 - Romero, G. E.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
SP - 109
EP - 118
KW - X-rays/ binaries/ gamma rays/ observations/ theory/ gamma-ray sources/ unidentified/ microquasars
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297..109G&db_key=AST&high=42a068d47531810
N2 - A subset of the unidentified EGRET gamma-ray sources with no active
galactic nucleus or other conspicuous counterpart appears to be
concentrated at medium latitudes. Their long-term variability and their
spatial distribution indicate that they are distinct from the more
persistent sources associated with the nearby Gould Belt. They exhibit a
large scale height of 1.3 ± 0.6 kpc above the Galactic plane.
Potential counterparts for these sources include microquasars accreting
from a low-mass star and spewing a continuous jet. Detailed calculations
have been performed of the jet inverse Compton emission in the radiation
fields from the star, the accretion disc, and a hot corona. Different
jet Lorentz factors, powers, and aspect angles have been explored. The
up-scattered emission from the corona predominates below 100 MeV whereas
the disc and stellar contributions are preponderant at higher energies
for moderate (~15o) and small
(~1o) aspect angles, respectively. Yet, unlike in the
high-mass, brighter versions of these systems, the external Compton
emission largely fails to produce the luminosities required for 5 to 10
kpc distant EGRET sources. Synchrotron-self-Compton emission appears as
a promising alternative.
ER -
TY - Journal
T1 - Preface
A1 - Cheng, K. S.
A1 - Romero, Gustavo E.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297...ixC&db_key=AST&high=42a068d47531810
N2 - Not Available
ER -
TY - Journal
T1 - Quaternary fault kinematics and stress tensors along the southern Caribbean from fault-slip data and focal mechanism solutions
A1 - Audemard, F. A.
A1 - Romero, G.
A1 - Rendon, H.
A1 - Cano, V.
JO - Earth Science Reviews
VL - 69
Y1 - 2005/3/1
SP - 181
EP - 233
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ESRv...69..181A&db_key=AST&high=42a068d47531810
N2 - Not Available
ER -
TY - Journal
T1 - Preface
A1 - Cheng, K. S.
A1 - Romero, Gustavo E.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/1/1
SP - 9
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297D...9C&db_key=AST&high=42a068d47531810
N2 - Not Available
ER -
TY - Journal
T1 - High-mass microquasars and low-latitude gamma-ray sources
A1 - Bosch-Ramon, V.
A1 - Romero, G. E.
A1 - Paredes, J. M.
JO - Astronomy and Astrophysics
VL - 429
Y1 - 2005/1/1
SP - 267
EP - 276
KW - X-rays: binaries/ stars: winds/ outflows/ gamma-rays: observations/ gamma-rays: theory
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...429..267B&db_key=AST&high=42a068d47531810
N2 - Population studies of unidentified EGRET sources suggest that there
exist at least three different populations of galactic gamma-ray
sources. One of these populations is formed by young objects distributed
along the galactic plane with a strong concentration toward the inner
spiral arms of the Galaxy. Variability, spectral and correlation
analysis indicate that this population is not homogeneous. In
particular, there is a subgroup of sources that display clear
variability in their gamma-ray fluxes on timescales from days to months.
Following the proposal by Kaufman Bernadó et al. (2002), we
suggest that this group of sources might be high-mass microquasars, i.e.
accreting black holes or neutron stars with relativistic jets and
early-type stellar companions. We present detailed inhomogeneous models
for the gamma-ray emission of these systems that include both external
and synchrotron self-Compton interactions. We have included effects of
interactions between the jet and all external photon fields to which it
is exposed: companion star, accretion disk, and hot corona. We make
broadband calculations to predict the spectral energy distribution of
the emission produced in the inner jet of these objects up to GeV
energies. The results and predictions can be tested by present and
future gamma-ray instruments like INTEGRAL, AGILE, and GLAST.
ER -
TY - Journal
T1 - Galaxy pairs in the 2dF survey - II. Effects of interactions on star formation in groups and clusters
A1 - Alonso, M. Sol
A1 - Tissera, Patricia B.
A1 - Coldwell, Georgina
A1 - Lambas, Diego G.
JO - Monthly Notices of the Royal Astronomical Society
VL - 352
Y1 - 2004/8/1
SP - 1081
EP - 1088
KW - galaxies: evolution/ galaxies: formation/ galaxies: general/ cosmology: theory
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.352.1081A&db_key=AST&high=42a068d47531810
N2 - We assess the effects of galaxy-galaxy interactions on star formation
(SF) by analysing pairs in groups and clusters of galaxies with virial
masses in the range 1013-1015Msolar
extracted from the 2dF Galaxy Redshift Survey (2dFGRS). We find that
galaxy pairs with relative separation rp < 15
h-1 kpc show significant SF activity in comparison with other
group member galaxies. Similar results were found for galaxy pairs in
the field (rp < 25 h-1 kpc) so that the nature
of SF driven by galaxy interactions is nearly independent of
environment, in spite of the general lower level of SF activity in
systems of galaxies. The above results reflect, on the one hand, the
local nature of SF induced by tidal interactions and, on the other, the
role played by the internal properties of galaxies. By using a 2dFGRS
mock catalogue we estimate the contamination by spurious pairs, finding
that our statistics are dominated by real pairs, in particular for close
relative separations, for which our study indicates significant SF
activity. We obtain a similar radial and relative velocity distribution
of the pairs with respect to the group centre compared with those of
other typical group members, so that galaxy pairs have no particular
location and dynamics within groups. Except for pairs with small
relative separations, which show significant SF activity, we find that
pairs in groups are systematically redder and have a lower present-day
SF activity than other group members.
ER -
TY - Journal
T1 - Linearized Stability of Charged Thin-Shell Wormholes
A1 - Eiroa, Ernesto F.
A1 - Romero, Gustavo E.
JO - General Relativity and Gravitation
VL - 36
Y1 - 2004/4/1
SP - 651
EP - 659
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GReGr..36..651E&db_key=AST&high=42a068d47531810
N2 - The linearized stability of charged thin shell wormholes under
spherically symmetric perturbations is analyzed. It is shown that the
presence of a large value of charge provides stabilization to the
system, in the sense that the constraints onto the equation of state are
less severe than for non-charged wormholes.
ER -
TY - Journal
T1 - High-Energy Gamma Rays from Stellar Associations
A1 - Torres, Diego F.
A1 - Domingo-Santamaría, Eva
A1 - Romero, Gustavo E.
JO - Astrophysical Journal
VL - 601
Y1 - 2004/1/1
SP - L75
EP - L78
KW - Gamma Rays: Observations/ Gamma Rays: Theory/ Stars: Early-Type
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...601L..75T&db_key=AST&high=42a068d47531810
N2 - It is proposed that TeV gamma-rays and neutrinos can be produced by
cosmic rays (CRs) through hadronic interactions in the innermost parts
of the winds of massive O and B stars. Convection prevents low-energy
particles from penetrating into the wind, leading to an absence of
MeV-GeV counterparts. It is argued that groups of stars located close to
the CR acceleration sites in OB stellar associations may be detectable
by ground-based Cerenkov telescopes.
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=42a068d47531810
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 - Did EGRET detect distant supernova remnants?
A1 - Torres, Diego F.
A1 - Romero, Gustavo E.
A1 - Dame, Thomas M.
A1 - Combi, Jorge A.
A1 - Butt, Yousaf M.
JO - Advances in Space Research
VL - 33
Y1 - 2004/1/1
SP - 450
EP - 455
KW - Supernova remnants/ EGRET/ Gamma ray source
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..33..450T&db_key=AST&high=42a068d47531810
N2 - It might be thought that supernova remnants (SNRs) more distant than a
few kiloparsec from Earth could not have been detected by the
high-energy gamma-ray experiment EGRET on board of NASA's Compton
Gamma-Ray Observatory. This work analyzes the observational status of
this statement in the light of new CO studies of SNRs.
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=42a068d47531810
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 - 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=42a068d47531810
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 - Testing the Binary Black Hole Paradigm through the Fe Kalpha Line Profile: Application to 3C 273
A1 - Torres, Diego F.
A1 - Romero, Gustavo E.
A1 - Barcons, Xavier
A1 - Lu, Youjun
JO - Astrophysical Journal
VL - 596
Y1 - 2003/10/1
SP - L31
EP - L34
KW - Accretion/ Accretion Disks/ Black Hole Physics/ Line: Profiles/ Galaxies: Quasars: Individual: Alphanumeric: 3C 273
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...596L..31T&db_key=AST&high=42a068d47531810
N2 - We propose the study of long-term variations in the Fe Kalpha line
profile as a discriminator for binary black hole (BH) systems. The
existence of a binary BH in the center of an active galaxy will produce
a particular signature in the evolution of the line profile, as a result
of disk precession. This signature is a periodic variation of the
position of the blue edge of the profile, accompanied by periodic change
of its intensity. We show that detection of the former is clearly within
the observational capabilities of planned X-ray missions. Detecting a
periodic variation of line profiles would provide the first direct
evidence for precessing disks in active galactic nuclei, as opposed to
the existing evidence supporting only the precession of jets. We apply
these ideas to 3C 273.
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=42a068d47531810
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 - Supernova remnants and gamma-ray sources
A1 - Torres, Diego F.
A1 - Romero, Gustavo E.
A1 - Dame, Thomas M.
A1 - Combi, Jorge A.
A1 - Butt, Yousaf M.
JO - Physics Reports
VL - 382
Y1 - 2003/8/1
SP - 303
EP - 380
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003PhR...382..303T&db_key=AST&high=42a068d47531810
N2 - Electronic Article Available from Elsevier Science.
ER -
TY - Journal
T1 - Neutrinos from Accreting Neutron Stars
A1 - Anchordoqui, Luis A.
A1 - Torres, Diego F.
A1 - McCauley, Thomas P.
A1 - Romero, Gustavo E.
A1 - Aharonian, Felix A.
JO - Astrophysical Journal
VL - 589
Y1 - 2003/5/1
SP - 481
EP - 486
KW - Gamma Rays: Observations/ Gamma Rays: Theory/ Neutrinos/ X-Rays: Binaries/ X-Rays: Individual: Alphanumeric: A0535+26
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...589..481A&db_key=AST&high=42a068d47531810
N2 - The magnetospheres of accreting neutron stars develop electrostatic gaps
with huge potential drops. Protons and ions, accelerated in these gaps
along the dipolar magnetic field lines to energies greater than 100 TeV,
can impact onto the surrounding accretion disk. A proton-induced cascade
develops, and charged pion decays produce nu emission. With extensive
disk shower simulations using DPMJET and GEANT4, we have calculated the
resulting nu spectrum. We show that the spectrum produced out of the
proton beam is a power law. We use this result to propose
accretion-powered X-ray binaries (with highly magnetized neutron stars)
as a new population of pointlike nu sources for kilometer-scale
detectors such as ICECUBE. As a particular example, we discuss the case
of A0535+26. We show that ICECUBE should find A0535+26 to be a periodic
nu source, one for which the formation and loss of its accretion disk
can be fully detected. Finally, we comment briefly on the possibility
that smaller telescopes such as AMANDA could also detect A0535+26 by
folding observations with the orbital period.
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=42a068d47531810
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 - Gravitational microlensing of gamma-ray blazars
A1 - Torres, Diego F.
A1 - Romero, Gustavo E.
A1 - Eiroa, Ernesto F.
A1 - Wambsganss, Joachim
A1 - Pessah, Martín E.
JO - Monthly Notices of the Royal Astronomical Society
VL - 339
Y1 - 2003/2/1
SP - 335
EP - 352
KW - gravitational lensing/ galaxies: active/ gamma-rays: observations/ gamma-rays: theory
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.339..335T&db_key=AST&high=42a068d47531810
N2 - We present a detailed study of the effects of gravitational microlensing
on compact and distant gamma-ray blazars. These objects have
gamma-ray-emitting regions that are small enough to be affected by
microlensing effects produced by stars lying in intermediate galaxies.
We compute the gravitational magnification taking into account effects
of the lensing and show that, whereas the innermost gamma-ray spheres
can be significantly magnified, there is little magnification either for
very high gamma-ray energies or for lower (radio) frequencies (because
these wavelengths are emitted from larger regions). We analyse the
temporal evolution of the gamma-ray magnification for sources moving in
a caustic pattern field, where the combined effects of thousands of
stars are taken into account using a numerical technique. We propose
that some of the unidentified gamma-ray sources (particularly some of
those lying at high galactic latitude with gamma-ray statistical
properties that are very similar to detected gamma-ray blazars) are
indeed the result of gravitational lensing magnification of background
undetected active galactic nuclei (AGN). This is partly supported from a
statistical point of view: we show herein as well, using the latest
information from the third EGRET catalogue, that high-latitude
gamma-ray sources have similar averaged properties to already detected
gamma-ray AGN. Some differences between both samples, regarding the
mean flux level, could also be understood within the lensing model. With
an adequate selection of lensing parameters, it is possible to explain a
variety of gamma-ray light curves with different time-scales,
including non-variable sources. The absence of strong radio counterparts
could be naturally explained by differential magnification in the
extended source formalism.
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=42a068d47531810
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 - Galaxy Peculiar Velocities and Infall onto Groups
A1 - Ceccarelli, M. L.
A1 - Valotto, C.
A1 - Lambas, D. G.
A1 - Padilla, N.
A1 - Giovanelli, R.
A1 - Haynes, M.
JO - Astrophysical Journal
VL - 622
Y1 - 2005/4/1
SP - 853
EP - 861
KW - Galaxies: Clusters: General
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...622..853C&db_key=AST&high=42a068d47503221
N2 - We perform statistical analysis to study the infall of galaxies onto
groups and clusters in the nearby universe. The study is based on the
Updated Zwicky Catalog and Southern Sky Redshift Survey 2 group catalogs
and peculiar velocity samples. We find a clear signature of infall of
galaxies onto groups over a wide range of scales
5h-1Mpc-1Mpc, with an infall amplitude
on the order of a few hundred kilometers per second. We obtain a
significant increase in the infall amplitude with group virial mass
(MV) and luminosity of group member galaxies (Lg).
Groups with MV<1013 Msolar show
infall velocities Vinf~=150 km s-1, whereas for
MV>1013 Msolar a larger infall is
observed, Vinf~=200 km s-1. Similarly, we find
that galaxies surrounding groups with Lg<1015
Lsolar have Vinf~=100 km s-1, whereas
for Lg>1015 Lsolar groups, the
amplitude of the galaxy infall can be as large as Vinf~=250
km s-1. The observational results are compared with the
results obtained from mock group and galaxy samples constructed from
numerical simulations, which include galaxy formation through
semianalytical models. We obtain a general agreement between the results
from the mock catalogs and the observations. The infall of galaxies onto
groups is suitably reproduced in the simulations, and, as in the
observations, larger virial mass and luminosity groups exhibit the
largest galaxy infall amplitudes. We derive estimates of the integrated
mass overdensities associated with groups by applying linear theory to
the infall velocities after correcting for the effects of distance
uncertainties obtained using the mock catalogs. The resulting
overdensities are consistent with a power law with delta~1 at r~10
h-1 Mpc.
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=42a068d47503221
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=42a068d47503221
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 - Detection of a Young Stellar Population in the Background of Open Clusters in the Third Galactic Quadrant
A1 - Carraro, Giovanni
A1 - Vázquez, Ruben A.
A1 - Moitinho, André
A1 - Baume, Gustavo
JO - Astrophysical Journal
VL - 630
Y1 - 2005/9/1
SP - L153
EP - L156
KW - Galaxy: Structure/ Stars: Hertzsprung-Russell Diagram/ Galaxy: Open Clusters and Associations: General/ Stars: General
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...630L.153C&db_key=AST&high=42a068d47505442
N2 - We report the detection of a young stellar population (<=100 Myr) in
the background of nine young open clusters belonging to a homogenous
sample of 30 star clusters in the third Galactic quadrant (at
217deg<=l<=260deg). Deep and accurate UBVRI
photometry allows us to measure model-independent age and distance for
the clusters and the background population with high confidence. This
population is exactly the same population (the blue plume) recently
detected in three intermediate-age open clusters and suggested to be a
<=1-2 Gyr old population belonging to the Canis Major (CMa)
overdensity (Bellazzini et al.; Martínez-Delgado et al.).
However, we find that the young population in those three clusters and
in six clusters of our sample follows the pattern of the Norma-Cygnus
spiral arm as defined by CO clouds remarkably well, while in the other
three program clusters it lies in the Perseus arm. We finally provide
one example (out of 21) of a cluster that does not show any background
population, demonstrating that this population is not ubiquitous toward
CMa.
ER -
TY - Journal
T1 - Revisiting the area of the open cluster Stock 16
A1 - Vázquez, R. A.
A1 - Baume, G. L.
A1 - Feinstein, C.
A1 - Nuñez, J. A.
A1 - Vergne, M. M.
JO - Astronomy and Astrophysics
VL - 435
Y1 - 2005/6/1
SP - 883
EP - 883
KW - open clusters and associations: individual: Stock 16/ errata/ addenda/ stars: imaging/ stars: luminosity function/ mass function
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...435..883V&db_key=AST&high=42a068d47505442
N2 - Not Available
ER -
TY - Journal
T1 - Revisiting the area of the open cluster Stock 16
A1 - Vázquez, R. A.
A1 - Baume, G. L.
A1 - Feinstein, C.
A1 - Nuñez, J. A.
A1 - Vergne, M. M.
JO - Astronomy and Astrophysics
VL - 430
Y1 - 2005/2/1
SP - 471
EP - 480
KW - Galaxy: open clusters and associations: individual: WR 50/ stars: luminosity function/ mass function\ Galaxy: open clusters and associations: individual: WR 51/ stars: imaging
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...430..471V&db_key=AST&high=42a068d47505442
N2 - Deep CCD UBV(RI)C photometry has been carried out in the area
of the open cluster Stock 16. The different photometric diagrams
indicate the presence of three superimposed stellar groups, all composed
of early type stars. The first of them, the cluster Stock 16, suffers
from slightly variable reddening with a mean color excess <
EB-V> = 0.51 . The second group, reddened by <
EB-V> = 0.84 , includes the Wolf-Rayet star WR 50 (a
WC7+OB), and the third one, with a mean < EB-V> = 1.18
, also includes another Wolf-Rayet star, WR 51 (a WN4+OB?). Our results
confirm the distance and reddening already stated for Stock 16 but
include new members. Concerning the other two highly reddened groups, we
show that the first one - located at a distance of 3600 pc - is probably
related to an anonymous OB association behind Cen OB1 also at 3600 pc
already mentioned in the literature; the other seems to be a distant OB
association - at more than 9000 pc - which may belong to the Scutum-Crux
spiral arm. In these two groups we find evidence that the absorption
law, AV/EB-V = R amounts to 4.0 approximately. The
ages of the different star populations in the zone range from 5 ×
106 yr to 6.4 × 106 yr for Stock 16, 8
× 106 for the second most reddened group and 5 ×
106 for the probable association in Scutum-Crux. A
determination of the IMF slope of Stock 16 was also carried out for
stars in the mass range 1.8 < M < 14 M⊙, giving
a normal value x = 1.3.
Based on observations collected at the University of Toronto Southern
Observatory (UTSO), 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/cgi-bin/qcat?J/A+A/430/471
ER -
TY - Journal
T1 - Spatial Structure of Regular and Chaotic Orbits in A Self-Consistent Triaxial Stellar System
A1 - Muzzio, J. C.
A1 - Carpintero, D. D.
A1 - Wachlin, F. C.
JO - Celestial Mechanics and Dynamical Astronomy
VL - 91
Y1 - 2005/1/1
SP - 173
EP - 190
KW - triaxial stellar systems/ stellar orbits/ chaotic motion
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005CeMDA..91..173M&db_key=AST&high=42a068d47505442
N2 - We created a triaxial stellar system through the cold dissipationless
collapse of 100,000 particles whose evolution was followed with a
multipolar code. Once an equilibrium system had been obtained, the
multipolar expansion was freezed and smoothed in order to get a
stationary smooth potential. The resulting model was self-consistent and
the orbits and Lyapunov exponents could then be computed for a randomly
selected sample of 3472 of the bodies that make up the system. More than
half of the orbits (52.7 % ) turned out to be chaotic. Regular orbits
were then classified using the frequency analysis automatic code of
Carpintero and Aguilar (1998, MNRAS 298(1), 1 21). We present plots of
the distributions of the different kinds of orbits projected on the
symmetry planes of the system. We distinguish chaotic orbits with only
one non-zero Lyapunov exponent from those with two non-zero exponents
and show that their spatial distributions differ, that of the former
being more similar to the one of the regular orbits. Most of the regular
orbits are boxes and boxlets, but the minor axis tubes play an important
role filling in the wasp waists of the boxes and helping to give a
lentil shape to the system. We see no problem in building stable
triaxial models with substantial amounts of chaotic orbits; the
difficulties found by other authors may be due not to a physical cause
but to a limitation of Schwarzschild's method.
ER -
TY - Journal
T1 - The young open cluster Markarian 50
A1 - Baume, Gustavo
A1 - Vázquez, Rubén A.
A1 - Carraro, Giovanni
JO - Monthly Notices of the Royal Astronomical Society
VL - 355
Y1 - 2004/12/1
SP - 475
EP - 484
KW - stars: imaging/ stars: individual: HD 219460/ stars: individual: WR 157/ stars: luminosity function/ mass function/ stars: Wolf-Rayet/ open clusters and associations: individual: Markarian 50
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.355..475B&db_key=AST&high=42a068d47505442
N2 - We report on a deep CCD UBV(RI)C photometric survey in the
region of the young open cluster Markarian 50. The new photometric data
allow us to extend the cluster membership down to V~ 17.5, about 2 mag
deeper than any previous investigation. On the basis of these data we
derive a distance d= 3460 +/- 350 pc (VO-MV= 12.7
+/- 0.2), which turns out to be only slightly lower than previous
estimates. The cluster presents differential reddening, with E(B-V)
values ranging from 0.69 to 1.1. The brightest member (HD 219460) is a
double star, which we separate photometrically for the first time,
providing individual magnitudes and colours for each component. One of
them is a Wolf-Rayet (WR) star and, according to evolutionary models,
the mass of its progenitor should be greater than ~20 Msolar.
The age obtained for the cluster is 7.5 +/- 2 Myr and the mass function
for the most massive stars (M > 1 Msolar) presents a slope
x~ 1.0.
ER -
TY - Journal
T1 - Optical polarization observations in Hogg 22 and NGC 6204
A1 - Martínez, R.
A1 - Vergne, M. M.
A1 - Feinstein, C.
JO - Astronomy and Astrophysics
VL - 419
Y1 - 2004/6/1
SP - 965
EP - 973
KW - ISM: dust/ extinction/ Galaxy: open clusters and associations: individual: NGC 6204/ Galaxy: open clusters and associations: individual: Hogg 22
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...419..965M&db_key=AST&high=42a068d47505442
N2 - We present new (UBVRI) multicolor linear polarimetric data for 22 of the
brightest stars in the area of the open clusters Hogg 22 and NGC 6204 to
study the properties of the ISM (interstellar medium) toward these
clusters and between them. The new data were incorporated in our data
set of previous observations (Waldhausen et al. \cite{waldhausen}),
resulting in 28 observed stars in the region. Our data yield for NGC
6204 a mean polarization percentage of
Plambda_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 -
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=42a068d47505442
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=42a068d47505442
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 - 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=42a068d47505442
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 - 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=42a068d47505442
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 - Imaging study of NGC 3372, the Carina nebula - I. UBVRIJHK photometry of Tr 14, Tr 15, Tr 16 and Car I
A1 - Tapia, Mauricio
A1 - Roth, Miguel
A1 - Vázquez, Rubén A.
A1 - Feinstein, Alejandro
JO - Monthly Notices of the Royal Astronomical Society
VL - 339
Y1 - 2003/2/1
SP - 44
EP - 62
KW - stars: formation/ HII regions/ ISM: individual: NGC 3372/ open clusters and associations: general
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.339...44T&db_key=AST&high=42a068d47505442
N2 - We present the results of a large-scale imaging photometric study of the
stellar population in the northern part of NGC 3372 in the UBVRIJHK
bands with a wavelength coverage from 0.33 to 2.5 mum. The
observations were made at Las Campanas Observatory. The optical CCD
mosaics cover an area approximately of 32 × 22 arcmin2
centred between the Tr 14 and Tr 16 clusters. The survey was extended to
cover 12 × 12 arcmin2 at the location of Tr 15.
Near-infrared NICMOS3 mosaics covering the areas occupied by these
clusters were obtained in the JHK photometric bands. By means of star
counts in V, the centres and sizes of each cluster were redetermined
yielding: Tr 14 (r= 264 arcsec), Tr 15 (r= 320 arcsec) and Tr 16 (r= 320
arcsec). It was confirmed that Cr 232 is not a true cluster. Multicolour
optical photometry was obtained for 4152 stars. Two colour and
colour-magnitude diagrams are presented and analysed for each individual
cluster and compared to those of the field. We confirm the widespread
variations in the dust density and also in the dust size distribution
leading to widely different values of AV and reddening laws
towards Tr 14 and Tr 16. No spatial patterns were found for these
variations. Spectroscopic parallaxes were computed and the results are
consistent with all three clusters being at a similar distance from the
Sun (= 2.7 kpc) but the data have shown very large scatter in
both AV and d. Analyses of the extinction-corrected
colour-magnitude diagrams suggest ages between 3 and 60 million years
for the stars in Tr 15 and between less than 1 and 6 million years for
Tr 14 and Tr 16. A small number of infrared-excess stars were found in
Tr 16 and Tr 14 but not in Tr 15. The distribution of stars in Tr 14
seen in the near-infrared suggests that this cluster is partially
embedded in a molecular cloud. This molecular cloud extends towards the
west reaching its highest density, marked by a CO peak emission, some
three arcmin to the south-west of the nucleus of Tr 14. The rich
ultraviolet field created by the Tr 14 stars ionizes most of the visible
HII region in its vicinity and most of the radio HII region Car I.
Evidence is found of ionization fronts leading into the molecular cloud,
which appears to be `wrapping' the Tr 14 cluster. Deep JHK images of the
Car I region reveal the presence of an embedded stellar population
illuminating a large infrared reflection nebula. It includes at least
one O9-B0 star associated with an ultracompact HII region. Nebulous 2.2
mum emission from three of the mid-infrared sources in the Tr 14
region is also found.
ER -
TY - Journal
T1 - The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI. Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
A1 - Kalberla, P. M. W.
A1 - Burton, W. B.
A1 - Hartmann, Dap
A1 - Arnal, E. M.
A1 - Bajaja, E.
A1 - Morras, R.
A1 - Pöppel, W. G. L.
JO - Astronomy and Astrophysics
VL - 440
Y1 - 2005/9/1
SP - 775
EP - 782
KW - surveys/ radio lines: ISM/ Galaxy: structure
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...440..775K&db_key=AST&high=42a068d47521649
N2 - We present the final data release of observations of lambda21-cm
emission from Galactic neutral hydrogen over the entire sky, merging the
Leiden/Dwingeloo Survey (LDS: Hartmann & Burton 1997, Atlas of
Galactic Neutral Hydrogen) of the sky north of delta = -30° with
the Instituto Argentino de Radioastronomía Survey (IAR: Arnal et
al. 2000, A&AS, 142, 35; and Bajaja et al. 2005, A&A, 440, 767)
of the sky south of delta = -25°. The angular resolution of the
combined material is HPBW ~ 0.6deg. The LSR velocity coverage spans the
interval -450 km s-1 to +400 km s-1, at a
resolution of 1.3 km s-1. The data were corrected for stray
radiation at the Institute for Radioastronomy of the University of Bonn,
refining the original correction applied to the LDS. The rms
brightness-temperature noise of the merged database is 0.07-0.09 K.
Residual errors in the profile wings due to defects in the correction
for stray radiation are for most of the data below a level of 20-40 mK.
It would be necessary to construct a telescope with a main beam
efficiency of etaMB î«¢ 99% to achieve the same accuracy.
The merged and refined material entering the LAB Survey of Galactic H i
is intended to be a general resource useful to a wide range of studies
of the physical and structural characteristices of the Galactic
interstellar environment. The LAB Survey is the most sensitive Milky Way
H i survey to date, with the most extensive coverage both spatially and
kinematically.
ER -
TY - Journal
T1 - A high sensitivity HI survey of the sky at delta ≤ -25 ° . Final data release
A1 - Bajaja, E.
A1 - Arnal, E. M.
A1 - Larrarte, J. J.
A1 - Morras, R.
A1 - Pöppel, W. G. L.
A1 - Kalberla, P. M. W.
JO - Astronomy and Astrophysics
VL - 440
Y1 - 2005/9/1
SP - 767
EP - 773
KW - surveys/ Galaxy: structure/ radio lines: ISM
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...440..767B&db_key=AST&high=42a068d47521649
N2 - We present the final data release of the high sensitivity lambda 21-cm
neutral hydrogen survey of the sky south of delta ≤ -25 °. A
total of 50 980 positions lying on a galactic coordinate grid with
points spaced by (Delta l, Delta b) = (0.5deg/cos b, 0.5deg) were
observed with the 30-m dish of the Instituto Argentino de
Radioastronomía (IAR). The angular resolution of the survey is
HPBW = 0.5deg 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 data are corrected for stray radiation and converted to
brightness temperatures.
ER -
TY - Journal
T1 - G287.84-0.82: an infrared star cluster in the Carina nebula
A1 - Hägele, G. F.
A1 - Albacete Colombo, J. F.
A1 - Barbá, R. H.
A1 - Bosch, G. L.
JO - Monthly Notices of the Royal Astronomical Society
VL - 355
Y1 - 2004/12/1
SP - 1237
EP - 1243
KW - stars: formation/ stars: pre-main-sequence/ open clusters and associations: individual: Carina nebula/ open clusters and associations: individual: G287.84-0.82/ open clusters and associations: individual: NGC 3372/ infrared: stars
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.355.1237H&db_key=AST&high=42a068d47521649
N2 - We have studied the properties of an infrared cluster embedded in the
gas and dust of the southern part of the Carina nebula (NGC 3372), where
the probable existence of current star formation has already been
predicted. We used mid-infrared (A and C bands) and near-infrared
(JHKs) images from the Midcourse Space Experiment and the
Two-Micron All-Sky Survey, respectively, combined with an optical
Halpha narrow-band filter image obtained at the Cerro Tololo
Inter-American Observatory. The infrared star cluster has at least 17
members, and its parameters, radius and stellar density are in very good
agreement with high- to intermediate-mass star formation scenarios. The
detected infrared sources have roughly the same intrinsic infrared
excess determined from their position in colour-colour and
colour-magnitude diagrams, suggesting that these objects could be
related to pre-main-sequence stars of high to intermediate mass.
Furthermore, we present a low-dispersion spectrum of the LS 1883 (O9.5V)
star located near the centre of the infrared cluster. The position of
this object in the colour-colour and colour-magnitude infrared diagrams
lies close to the reddening vector of a zero-age main-sequence O9V
spectral-type star, and it seems to be the first star of this cluster to
emerge. All these facts are consistent with the current star-forming
scenarios associated with highly embedded star clusters.
ER -
TY - Journal
T1 - Carina's defiant Finger: HST observations of a photoevaporating globule in NGC 3372*
A1 - Smith, Nathan
A1 - Barbá, Rodolfo H.
A1 - Walborn, Nolan R.
JO - Monthly Notices of the Royal Astronomical Society
VL - 351
Y1 - 2004/7/1
SP - 1457
EP - 1470
KW - stars: formation/ ISM: globules/ HII regions/ ISM: individual: NGC 3372
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.351.1457S&db_key=AST&high=42a068d47521649
N2 - We present Hubble Space Telescope Wide Field Planetary Camera 2 images
of a prominent externally ionized molecular globule in the Carina Nebula
(NGC 3372), supplemented with ground-based infrared images and
visual-wavelength spectra. This molecular globule has a shape resembling
a human hand, with an extended finger that points toward its likely
source of ionizing radiation. Following an analysis of the spatially
resolved ionization structure and spectrum of the photoevaporative flow
from the Finger, we conclude that the dominant ionizing source is either
the WNL star WR25 (HD 93162), the adjacent O4 If-type star Tr16-244, or
perhaps both. We estimate a mass-loss rate of ~2 × 10-5
Msolar yr-1 from the main evaporating surface of
the globule, suggesting a remaining lifetime of
105.3-106 yr. We find a total mass for the entire
globule of more than 6 Msolar, in agreement with previous
estimates. The hydrogen column density through the globule derived from
extinction measurements is a few times 1022 cm-2,
so the photodissociation region behind the ionization front should be
limited to a thin layer compared to the size of the globule, in
agreement with the morphology seen in H2 images. Although a
few reddened stars are seen within the boundary of the globule in
near-infrared continuum images, these may be background stars. We do not
detect a reddened star at the apex of the finger, for example, down to a
limiting magnitude of mK~= 17. However, considering the
physical properties of the globule and the advancing ionization front,
it appears that future star formation is likely in the Finger globule,
induced by radiation-driven implosion.
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=42a068d47521649
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 - 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=42a068d47521649
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 - The globular cluster systems of NGC 3258 and NGC 3268 in the Antlia cluster
A1 - Dirsch, B.
A1 - Richtler, T.
A1 - Bassino, L. P.
JO - Astronomy and Astrophysics
VL - 408
Y1 - 2003/9/1
SP - 929
EP - 939
KW - galaxies: elliptical and lenticular/ cD/ galaxies: individual: NGC 3258/ NGC 3268/ NGC 3269/ galaxies: star clusters/ galaxies: stellar content/ galaxies: structure
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...408..929D&db_key=AST&high=42a068d47521649
N2 - The Antlia galaxy cluster is the third nearest galaxy cluster after
Virgo and Fornax. We used the wide-field MOSAIC camera of the 4-m CTIO
telescope to search in the brightest cluster galaxies for globular
cluster systems, which were detected in the two larger ellipticals - NGC
3258 and NGC 3268. These galaxies each contain several thousand
clusters; NGC 3258 more than NGC 3268. The color distributions of the
globular cluster systems are clearly bimodal. The peak colors agree with
those of other ellipticals. The radial number density profiles of the
globular cluster systems are indistinguishable for the two galaxies and
no difference in the distribution of red and blue clusters - as observed
in other elliptical galaxies - can be seen. The light profile of NGC
3268 appears to be similar to that of NGC 1399, the central galaxy of
the Fornax cluster. NGC 3258 has a light profile which is steeper at
large radii. Both galaxies exhibit color gradients, becoming bluer
outwards. In NGC 3268, the color and morphology in the inner 3 arcsec
indicate the presence of an inner dusty disk. The globular cluster
systems closely trace the galaxy light in the studied radial regime. The
elongation of the cluster systems of both galaxies is approximately
aligned at large radii with the connecting axis of the two galaxies. We
find specific frequencies within a radial range of 4 arcmin of
SN=3.0+/-2.0 for NGC 3268 and SN=6.0+/-2.5 for NGC
3258.
As a byproduct resulting from surveying our wide-field frames, we
describe a strange absorption feature in the Antlia spiral galaxy NGC
3269, which we argue might be a tiny galactic dust cloud projected onto
NGC 3269.
Based on observations collected at the Cerro Tololo Inter-American
Observatory (CTIO).
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=42a068d47521649
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 - 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=42a068d47521649
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 - 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=42a068d47521649
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 - The Globular Cluster System of NGC 1399. I. A Wide-Field Photometric Study
A1 - Dirsch, B.
A1 - Richtler, T.
A1 - Geisler, D.
A1 - Forte, J. C.
A1 - Bassino, L. P.
A1 - Gieren, W. P.
JO - Astronomical Journal
VL - 125
Y1 - 2003/4/1
SP - 1908
EP - 1925
KW - Galaxies: Elliptical and Lenticular/ cD/ Galaxies: Halos/ Galaxies: Individual: NGC Number: NGC 1399/ Galaxies: Photometry/ Galaxies: Star Clusters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....125.1908D&db_key=AST&high=42a068d47521649
N2 - We present a photometric investigation of the globular cluster
population of NGC 1399, the central galaxy in the Fornax cluster, in
Washington C and Kron R filters within a field of 36'×36',
corresponding to about 200×200 kpc at the Fornax distance. This is
the largest area around this galaxy ever studied with CCD photometry.
The cluster system of NGC 1399 is found to extend farther than 100 kpc
away from the galaxy. The color distribution exhibits a pronounced
bimodality. Within a radial distance of about 55 kpc, the red clusters
are more strongly concentrated toward the center than the blue clusters.
At larger radii, the surface density profiles of the clusters are
indistinguishable and match well the distribution of the galaxy light.
Over the entire radial distance range, the surface brightness profile of
NGC 1399 can be very well fitted by a power law with an exponent of
-1.85 and a core radius of 3.3". No steepening of the luminosity profile
can be detected at large radii. We suggest that the power-law profile of
NGC 1399 results from the galaxy being embedded in a large dark matter
halo, which prevents the stellar density profile from steepening
outward. The cluster system contains 6450+/-700 clusters and the
specific frequency is found to be 5.1+/-1.2 in the V band. While NGC
1399 shows a pronounced color gradient the nearby comparison galaxy NGC
1404 does not show such a gradient. Using simple assumptions about the
underlying population that formed during the same star formation event
as the globular clusters, we present a model in which we use radially
changing local specific frequencies for the red and blue subpopulations
to fit the observations. We find that within 7' the required specific
frequency of the blue clusters alone is a factor of approximately 3
larger than that of the red ones. Outside this radius, however, both
populations have the same high local specific frequency of around 8 and
13 (blue and red clusters, respectively).
Based partly on observations collected at the European Southern
Observatory, Cerro Paranal, Chile; ESO program 66.B-0393.
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=42a068d47521649
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 - A photometric study of the old open clusters Berkeley 73, Berkeley 75 and Berkeley 25
A1 - Carraro, G.
A1 - Geisler, D.
A1 - Moitinho, A.
A1 - Baume, G.
A1 - Vázquez, R. A.
JO - Astronomy and Astrophysics
VL - 442
Y1 - 2005/11/1
SP - 917
EP - 924
KW - open clusters and associations: individual:/ Berkeley 73/ Berkeley 75/ Berkeley 25/ open clusters and associations: general/ Hertzprung-Russell (HR) and C-M diagrams
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...442..917C&db_key=AST&high=42a068d47524120
N2 - CCD BVI photometry of the faint open clusters Berkeley 73, Berkeley 75
and Berkeley 25 are presented. The two latter are previously unstudied
clusters to our knowledge. While Berkeley 73 is found to be of
intermediate-age (about 1.5 Gyr old), Berkeley 75 and Berkeley 25 are
old clusters, with ages greater than 3.0 Gyr. We provide also estimates
of the clusters size. All these clusters lie far away from the Galactic
Center, at R_GC ≥ 16 kpc, and quite high on the Galactic plane, at
|Z⊙| ≥ 1.5 kpc. They are therefore important targets
to probe the properties of the structure of the Galaxy in this
direction, where the Canis Major over-density has been discovered to be
located.
ER -
TY - Journal
T1 - The intermediate-age open clusters Ruprecht 61, Czernik 32, NGC 2225 and 2262
A1 - Carraro, G.
A1 - Baume, G.
A1 - Vázquez, R. A.
A1 - Moitinho, A.
A1 - Geisler, D.
JO - Monthly Notices of the Royal Astronomical Society
VL - 362
Y1 - 2005/9/1
SP - 649
EP - 656
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.362..649C&db_key=AST&high=42a068d47524120
N2 - We present the first BVI CCD photometry to V= 22.0 of four fields
centred on the region of the southern Galactic star clusters Ruprecht
61, Czernik 32, NGC 2225 and 2262 and of four displaced control fields.
These clusters have never been studied before, and we provide for the
first time estimates of their fundamental parameters, specifically
radial extent, age, distance and reddening. We find that the four
clusters are all of intermediate age (around 1Gyr), close to the Sun and
possess lower than solar metal abundance.
ER -
TY - Journal
T1 - Detection of a Young Stellar Population in the Background of Open Clusters in the Third Galactic Quadrant
A1 - Carraro, Giovanni
A1 - Vázquez, Ruben A.
A1 - Moitinho, André
A1 - Baume, Gustavo
JO - Astrophysical Journal
VL - 630
Y1 - 2005/9/1
SP - L153
EP - L156
KW - Galaxy: Structure/ Stars: Hertzsprung-Russell Diagram/ Galaxy: Open Clusters and Associations: General/ Stars: General
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...630L.153C&db_key=AST&high=42a068d47524120
N2 - We report the detection of a young stellar population (<=100 Myr) in
the background of nine young open clusters belonging to a homogenous
sample of 30 star clusters in the third Galactic quadrant (at
217deg<=l<=260deg). Deep and accurate UBVRI
photometry allows us to measure model-independent age and distance for
the clusters and the background population with high confidence. This
population is exactly the same population (the blue plume) recently
detected in three intermediate-age open clusters and suggested to be a
<=1-2 Gyr old population belonging to the Canis Major (CMa)
overdensity (Bellazzini et al.; Martínez-Delgado et al.).
However, we find that the young population in those three clusters and
in six clusters of our sample follows the pattern of the Norma-Cygnus
spiral arm as defined by CO clouds remarkably well, while in the other
three program clusters it lies in the Perseus arm. We finally provide
one example (out of 21) of a cluster that does not show any background
population, demonstrating that this population is not ubiquitous toward
CMa.
ER -
TY - Journal
T1 - Multiwavelength studies of WR 21a and its surroundings
A1 - Benaglia, P.
A1 - Romero, G. E.
A1 - Koribalski, B.
A1 - Pollock, A. M. T.
JO - Astronomy and Astrophysics
VL - 440
Y1 - 2005/9/1
SP - 743
EP - 750
KW - stars: early-type/ stars: individual: WR 21a/ stars: winds/ outflows/ radio continuum:/ stars/ ISM: bubbles/ gamma-rays: observations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...440..743B&db_key=AST&high=42a068d47524120
N2 - We present results of high-resolution radio continuum observations
towards the binary star WR 21a (Wack 2134) obtained with the Australia
Telescope Compact Array (ATCA) at 4.8 and 8.64 GHz. We detected the
system at 4.8 GHz (6 cm) with a flux density of 0.25±0.06 mJy and
set an upper limit of 0.3 mJy at 8.64 GHz (3 cm). The derived spectral
index of alpha < 0.3 (Snu âˆ
nualpha) suggests the presence of non-thermal emission,
probably originating in a colliding-wind region. A second, unrelated
radio source was detected ~10 arcsec north of WR 21a at (RA,
Dec)J2000=(10h25m56.49s, -57°48
arcmin34.4 arcsec), with flux densities of 0.36 and 0.55 mJy at 4.8 and
8.64 GHz, respectively, resulting in alpha = 0.72. H i observations in
the area are dominated by absorption against the prominent H ii region
RCW 49. Analysis of a complete set of archived X-ray observations of WR
21a confirms its strong variability but throws into doubt previous
suggestions by Reig (1999) of a period of years for the system. Finally,
we comment on the association with the nearby EGRET source 3EG
J1027-5817.
ER -
TY - Journal
T1 - The intermediate-age open clusters Ruprecht 4, Ruprecht 7 and Pismis 15
A1 - Carraro, G.
A1 - Geisler, D.
A1 - Baume, G.
A1 - Vázquez, R.
A1 - Moitinho, A.
JO - Monthly Notices of the Royal Astronomical Society
VL - 360
Y1 - 2005/6/1
SP - 655
EP - 661
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.360..655C&db_key=AST&high=42a068d47524120
N2 - We report on BVI CCD photometry to V= 22.0 for three fields centred on
the region of the Galactic star clusters Ruprecht 4, Ruprecht 7 and
Pismis 15 and on three displaced control fields. Ruprecht 4 and Pismis
15 have never been studied before, and we provide, for the first time,
estimates of their fundamental parameters, namely, radial extent, age,
distance and reddening. Ruprecht 7 (Berkeley 33), however, was studied
by Mazur, Kaluzny & Krzeminski. We find that the three clusters are
all of intermediate age (0.8-1.3 Gyr), and with a metallicity close to
or lower than solar.
ER -
TY - Journal
T1 - Luminosity and mass functions of galactic open clusters. II. NGC 4852
A1 - Carraro, G.
A1 - Baume, G.
A1 - Piotto, G.
A1 - Méndez, R. A.
A1 - Schmidtobreick, L.
JO - Astronomy and Astrophysics
VL - 436
Y1 - 2005/6/1
SP - 527
EP - 534
KW - open clusters and associations: individual: NGC 4852/ Hertzsprung-Russell (HR) and C-M diagrams
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...436..527C&db_key=AST&high=42a068d47524120
N2 - We present wide-field deep {UBVI} photometry for the previously
unstudied open cluster NGC 4852 down to a limiting magnitude I~24,
obtained from observations taken with the Wide Field Imager camera
on-board the MPG/ESO 2.2 m telescope at La Silla (ESO, Chile). These
data are used to obtain the first estimate of the cluster basic
parameters, to study the cluster spatial extension by means of star
counts, and to derive the Luminosity (LF) and Mass Function (MF). The
cluster radius turns out to be 5.0±1.0 arcmin. The cluster
emerges clearly from the field down to V=20 mag. At fainter magnitudes,
it is completely confused with the general Galactic disk field. The
stars inside this region define a young open cluster (200 million years
old) 1.1 kpc far from the Sun (m-M = 11.60, E(B-V) = 0.45). The Present
Day Mass Functions (PDMF) from the V photometry is one of the most
extended in mass obtained to date, and can be represented as a power-law
with a slope alpha = 2.3±0.3 and (the Salpeter MF in this
notation has a slope alpha = 2.35), in the mass range 3.2 ≤
{m}/{m⊙} ≤ 0.6. Below this mass, the MF cannot be
considered as representative of the cluster MF, as the cluster merges
with the field and therefore the MF is the result of the combined effect
of strong irregularities in the stellar background and interaction of
the cluster with the dense Galactic field. The cluster total mass at the
limiting magnitude results to be 2570±210 M⊙.
ER -
TY - Journal
T1 - Revisiting the area of the open cluster Stock 16
A1 - Vázquez, R. A.
A1 - Baume, G. L.
A1 - Feinstein, C.
A1 - Nuñez, J. A.
A1 - Vergne, M. M.
JO - Astronomy and Astrophysics
VL - 435
Y1 - 2005/6/1
SP - 883
EP - 883
KW - open clusters and associations: individual: Stock 16/ errata/ addenda/ stars: imaging/ stars: luminosity function/ mass function
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...435..883V&db_key=AST&high=42a068d47524120
N2 - Not Available
ER -
TY - Journal
T1 - Analytical Proper Elements for the Hilda Asteroids I: Construction of a Formal Solution
A1 - Miloni, O.
A1 - Ferraz-Mello, S.
A1 - Beaugé, C.
JO - Celestial Mechanics and Dynamical Astronomy
VL - 92
Y1 - 2005/4/1
SP - 89
EP - 111
KW - Hilda asteroids/ perturbation theory/ proper elements
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005CeMDA..92...89M&db_key=AST&high=42a068d47524120
N2 - In this paper, we present the mathematical basis for the calculation of
proper elements for asteroids in 3:2 mean-motion resonance with Jupiter
from their osculating Keplerian elements. The method is based on a new
resonant Lie-series perturbation theory (Ferraz-Mello, 1997, 2002),
which allows the construction of formal solutions in cases where
resonant and long-period angles appear simultaneously. For the
disturbing function, we used the Beaugé's expansion
(Beaugé, 1996), adapted to include short period terms. In this
paper, the theory is restricted to the planar case and only the
perturbations due to Jupiter are considered.
ER -
TY - Journal
T1 - The Orbits of the Extrasolar Planets HD 82943c and b
A1 - Ferraz-Mello, S.
A1 - Michtchenko, T. A.
A1 - Beaugé, C.
JO - Astrophysical Journal
VL - 621
Y1 - 2005/3/1
SP - 473
EP - 481
KW - Celestial Mechanics/ Stars: Planetary Systems/ Stars: Individual: Henry Draper Number: HD 82943
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...621..473F&db_key=AST&high=42a068d47524120
N2 - The published orbits of the planets HD 82943b and HD 82943c correspond
to a system bound to a catastrophic event in less than 100,000 yr.
Alternative sets of elements and masses, which fit the available
observational data and correspond to regular motions, are presented in
this paper. The planets HD 82943c and b are in a 2:1 mean-motion
resonance and are trapped in the neighborhood of a (0, 0) apsidal
corotation.
ER -
TY - Journal
T1 - The Vela-Puppis open clusters Pismis 8 and Pismis 13
A1 - Giorgi, E. E.
A1 - Baume, G.
A1 - Solivella, G.
A1 - Vázquez, R. A.
JO - Astronomy and Astrophysics
VL - 432
Y1 - 2005/3/1
SP - 491
EP - 500
KW - Galaxy: open clusters and associations: individual: Pismis 8/ Pismis 13/ stars: luminosity function/ mass function/ stars: Hertzsprung-Russell (H-R) and C-M diagrams
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...432..491G&db_key=AST&high=42a068d47524120
N2 - CCD UBVI imaging photometry was carried out in the fields of the open
clusters Pismis 8 and Pismis 13, located in the Vela-Puppis region in
our Galaxy. MK spectral types have also been determined for a number of
stars located in the fields of these two clusters which were used to
secure membership among the brightest stars. Since our photometry goes
to a fainter limit than previous studies we could provide better
reddening, distance and age determinations. Both clusters are located
close to the edge of the local arm in the third quadrant. Pismis 8 is a
cluster about 5-7 My old located at 2000 pc from the Sun, while Pismis
13 was found at 2750 pc with a probable age of about 100 My. The
estimate of the slopes of the mass functions in both cases yielded x≈
1.7 and x≈ 2.1 for Pismis 8 and 13 respectively.
Based on observations collected at the University of Toronto Southern
Observatory, Las Campanas, Chile, and the Complejo Astronómico El
Leoncito, San Juan, Argentina. 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/432/491
ER -
TY - Journal
T1 - New giant HII regions in the southern sky
A1 - Firpo, V.
A1 - Bosch, G.
A1 - Morrell, N.
JO - Monthly Notices of the Royal Astronomical Society
VL - 356
Y1 - 2005/2/1
SP - 1357
EP - 1361
KW - HII regions/ galaxies: individual: NGC 2997/ galaxies: individual: NGC 7552/ galaxies: starburst
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.356.1357F&db_key=AST&high=42a068d47524120
N2 - We present results of a search for giant HII regions in southern
galaxies. Using high-resolution spectra, obtained with the Magellan
Inamori Kyocera Echelle (MIKE) at the Las Campanas Magellan II
telescope, we were able to resolve the emission-line profiles and
determine the intrinsic velocity dispersion of the ionized gas. Out of
four observed regions, selected from previous CCD narrow-band
photometry, we detected three HII regions showing supersonic velocity
dispersion, characteristic of giant HII regions, and their location in
diagnostic diagrams suggests that a powerful starburst is the source of
ionization energy.
ER -
TY - Journal
T1 - Revisiting the area of the open cluster Stock 16
A1 - Vázquez, R. A.
A1 - Baume, G. L.
A1 - Feinstein, C.
A1 - Nuñez, J. A.
A1 - Vergne, M. M.
JO - Astronomy and Astrophysics
VL - 430
Y1 - 2005/2/1
SP - 471
EP - 480
KW - Galaxy: open clusters and associations: individual: WR 50/ stars: luminosity function/ mass function\ Galaxy: open clusters and associations: individual: WR 51/ stars: imaging
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...430..471V&db_key=AST&high=42a068d47524120
N2 - Deep CCD UBV(RI)C photometry has been carried out in the area
of the open cluster Stock 16. The different photometric diagrams
indicate the presence of three superimposed stellar groups, all composed
of early type stars. The first of them, the cluster Stock 16, suffers
from slightly variable reddening with a mean color excess <
EB-V> = 0.51 . The second group, reddened by <
EB-V> = 0.84 , includes the Wolf-Rayet star WR 50 (a
WC7+OB), and the third one, with a mean < EB-V> = 1.18
, also includes another Wolf-Rayet star, WR 51 (a WN4+OB?). Our results
confirm the distance and reddening already stated for Stock 16 but
include new members. Concerning the other two highly reddened groups, we
show that the first one - located at a distance of 3600 pc - is probably
related to an anonymous OB association behind Cen OB1 also at 3600 pc
already mentioned in the literature; the other seems to be a distant OB
association - at more than 9000 pc - which may belong to the Scutum-Crux
spiral arm. In these two groups we find evidence that the absorption
law, AV/EB-V = R amounts to 4.0 approximately. The
ages of the different star populations in the zone range from 5 ×
106 yr to 6.4 × 106 yr for Stock 16, 8
× 106 for the second most reddened group and 5 ×
106 for the probable association in Scutum-Crux. A
determination of the IMF slope of Stock 16 was also carried out for
stars in the mass range 1.8 < M < 14 M⊙, giving
a normal value x = 1.3.
Based on observations collected at the University of Toronto Southern
Observatory (UTSO), 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/cgi-bin/qcat?J/A+A/430/471
ER -
TY - Journal
T1 - G287.84-0.82: an infrared star cluster in the Carina nebula
A1 - Hägele, G. F.
A1 - Albacete Colombo, J. F.
A1 - Barbá, R. H.
A1 - Bosch, G. L.
JO - Monthly Notices of the Royal Astronomical Society
VL - 355
Y1 - 2004/12/1
SP - 1237
EP - 1243
KW - stars: formation/ stars: pre-main-sequence/ open clusters and associations: individual: Carina nebula/ open clusters and associations: individual: G287.84-0.82/ open clusters and associations: individual: NGC 3372/ infrared: stars
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.355.1237H&db_key=AST&high=42a068d47524120
N2 - We have studied the properties of an infrared cluster embedded in the
gas and dust of the southern part of the Carina nebula (NGC 3372), where
the probable existence of current star formation has already been
predicted. We used mid-infrared (A and C bands) and near-infrared
(JHKs) images from the Midcourse Space Experiment and the
Two-Micron All-Sky Survey, respectively, combined with an optical
Halpha narrow-band filter image obtained at the Cerro Tololo
Inter-American Observatory. The infrared star cluster has at least 17
members, and its parameters, radius and stellar density are in very good
agreement with high- to intermediate-mass star formation scenarios. The
detected infrared sources have roughly the same intrinsic infrared
excess determined from their position in colour-colour and
colour-magnitude diagrams, suggesting that these objects could be
related to pre-main-sequence stars of high to intermediate mass.
Furthermore, we present a low-dispersion spectrum of the LS 1883 (O9.5V)
star located near the centre of the infrared cluster. The position of
this object in the colour-colour and colour-magnitude infrared diagrams
lies close to the reddening vector of a zero-age main-sequence O9V
spectral-type star, and it seems to be the first star of this cluster to
emerge. All these facts are consistent with the current star-forming
scenarios associated with highly embedded star clusters.
ER -
TY - Journal
T1 - The young open cluster Markarian 50
A1 - Baume, Gustavo
A1 - Vázquez, Rubén A.
A1 - Carraro, Giovanni
JO - Monthly Notices of the Royal Astronomical Society
VL - 355
Y1 - 2004/12/1
SP - 475
EP - 484
KW - stars: imaging/ stars: individual: HD 219460/ stars: individual: WR 157/ stars: luminosity function/ mass function/ stars: Wolf-Rayet/ open clusters and associations: individual: Markarian 50
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.355..475B&db_key=AST&high=42a068d47524120
N2 - We report on a deep CCD UBV(RI)C photometric survey in the
region of the young open cluster Markarian 50. The new photometric data
allow us to extend the cluster membership down to V~ 17.5, about 2 mag
deeper than any previous investigation. On the basis of these data we
derive a distance d= 3460 +/- 350 pc (VO-MV= 12.7
+/- 0.2), which turns out to be only slightly lower than previous
estimates. The cluster presents differential reddening, with E(B-V)
values ranging from 0.69 to 1.1. The brightest member (HD 219460) is a
double star, which we separate photometrically for the first time,
providing individual magnitudes and colours for each component. One of
them is a Wolf-Rayet (WR) star and, according to evolutionary models,
the mass of its progenitor should be greater than ~20 Msolar.
The age obtained for the cluster is 7.5 +/- 2 Myr and the mass function
for the most massive stars (M > 1 Msolar) presents a slope
x~ 1.0.
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=42a068d47524120
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 - Collisional Origin of Families of Irregular Satellites
A1 - Nesvorný, David
A1 - Beaugé, Cristian
A1 - Dones, Luke
JO - Astronomical Journal
VL - 127
Y1 - 2004/3/1
SP - 1768
EP - 1783
KW - Planets and Satellites: Formation
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127.1768N&db_key=AST&high=42a068d47524120
N2 - A distinctive feature of the irregular moons of the giant planets is
their orbital grouping. Previously, the prograde and retrograde groups
of irregular moons at Jupiter were believed to be groups of fragments
produced by the disruption of two large moons. More recently, we have
shown that the retrograde group has not one but probably four or more
parent bodies. We also found that fragments were launched from two of
the four identified parent moons, producing two clusters of irregular
moons with members of each group having similar orbits. Named the Ananke
and Carme families, these two groups consist of seven and nine known
member moons, respectively. The origin of this orbital clustering is
unknown. Current rates of collisions among satellites in the retrograde
group are too low to explain them. Collisions with cometary impactors
are even less likely. Groups of irregular satellites with similar
inclinations at Saturn are also yet to be explained. It is conceivable
that the satellite families are remnants from early epochs of solar
system formation when impactors were more numerous. In this paper we
investigate the possibility that satellite families formed via
collisions between large parent moons and stray planetesimals. We find
that the Ananke and Carme families at Jupiter could indeed have been
produced by this mechanism, unless the residual disk of planetesimals in
heliocentric orbit was already severely depleted when the irregular
satellites formed. Conversely, we find that formation of the Himalia
group of prograde Jovian satellites by the same mechanism is unlikely
unless a massive residual planetesimal disk was still present when the
progenitor moon of the Himalia group was captured. We place constraints
on the mass of the residual disk (1) when satellites were captured, and
(2) when the Ananke and Carme families formed. These values depend
sensitively on the assumed size-frequency distribution of planetesimals.
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=42a068d47524120
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 - The old open clusters Saurer A, B and C revisited
A1 - Carraro, Giovanni
A1 - Baume, Gustavo
JO - Monthly Notices of the Royal Astronomical Society
VL - 346
Y1 - 2003/11/1
SP - 18
EP - 26
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.346...18C&db_key=AST&high=42a068d47524120
N2 - We report deep (V~ 24.0) VI CCD photometry of three fields centred in
the regions of the old open clusters Saurer A, B and C. In the case of
Saurer A, which is considered one of the oldest known open clusters, we
also provide a comparison field. From the analysis of the photometry we
claim that Saurer A is as old as M67 (~5 Gyr), but more metal-poor (Z=
0.008). Moreover, it turns out to be the open cluster with the largest
galactocentric distance so far detected.
As for Saurer B, it closely resembles NGC 2158, and indeed is of
intermediate age (1.8-2.2 Gyr) and significantly reddened. In this case
we revise both the age and the distance with respect to previous
studies, but we are not able to establish clearly the cluster metal
abundance.
Finally, Saurer C has an age of about 2 Gyr, but we emphasize that the
precise determination of its properties is hampered by the heavy field
star contamination.
All of the photometry is available at the WEBDA data base:
http://obswww.unige.ch/webda/navigation.html.
ER -
TY - Journal
T1 - Chandra/Very Large Array Follow-Up of TeV J2032+4131, the Only Unidentified TeV Gamma-Ray Source
A1 - Butt, Yousaf M.
A1 - Benaglia, Paula
A1 - Combi, Jorge A.
A1 - Corcoran, Michael
A1 - Dame, Thomas M.
A1 - Drake, Jeremy
A1 - Kaufman Bernadó, Marina
A1 - Milne, Peter
A1 - Miniati, Francesco
A1 - Pohl, Martin
A1 - Reimer, Olaf
A1 - Romero, Gustavo E.
A1 - Rupen, Michael
JO - Astrophysical Journal
VL - 597
Y1 - 2003/11/1
SP - 494
EP - 512
KW - Gamma Rays: Observations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...597..494B&db_key=AST&high=42a068d47524120
N2 - The High Energy Gamma Ray Astronomy (HEGRA) Cerenkov telescope array
group recently reported a steady and extended unidentified TeV gamma-ray
source lying at the outskirts of Cygnus OB2. This is the most massive
stellar association known in the Galaxy, estimated to contain ~2600
OB-type members alone. It has been previously argued that the
large-scale shocks and turbulence induced by the multiple interacting
supersonic winds from the many young stars in such associations may play
a role in accelerating Galactic cosmic rays. Indeed, Cyg OB2 also
coincides with the nonvariable MeV-GeV range unidentified EGRET source,
3EG 2033+4118. We report on the near-simultaneous follow-up observations
of the extended TeV source region with the Chandra X-Ray Observatory and
the Very Large Array radio telescope, obtained in order to explore this
possibility. Analysis of the CO, H I, and IRAS 100 mum emissions shows
that the TeV source region coincides with an outlying subgroup of
powerful OB stars that have evacuated or destroyed much of the ambient
atomic, molecular, and dust material and that may be related to the very
high energy emissions. An interesting supernova-remnant-like structure
is also revealed near the TeV source region in the CO, H I, and radio
emission maps. Applying a numerical simulation that accurately tracks
the radio to gamma-ray emission from primary hadrons as well as primary
and secondary e+/-, we find that the broadband spectrum of
the TeV source region favors a predominantly nucleonic-rather than
electronic-origin for the high-energy flux, although deeper X-ray and
radio observations will help confirm this. A very reasonable, ~0.1%,
conversion efficiency of Cyg OB2's extreme stellar wind mechanical
luminosity to nucleonic acceleration to ~PeV (1015 eV)
energies is sufficient to explain the multifrequency emissions.
ER -
TY - Journal
T1 - NGC 1883: a neglected intermediate-age open cluster located in the outskirts of the Galactic disc
A1 - Carraro, Giovanni
A1 - Baume, Gustavo
A1 - Villanova, Sandro
JO - Monthly Notices of the Royal Astronomical Society
VL - 343
Y1 - 2003/8/1
SP - 547
EP - 551
KW - Hertzsprung/ Russell (HR) diagram/ open clusters and associations: general/ open clusters and associations: individual: NGC 1883
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003MNRAS.343..547C&db_key=AST&high=42a068d47524120
N2 - We report on BVI CCD photometry of a field centred in the region of the
open cluster NGC 1883, down to V= 21. This cluster has never been
studied so far; we provide, for the first time, estimates of its
fundamental parameters - namely radial extent, age, distance and
reddening. We find that the cluster has a radius of about 2.5 arcmin,
and shows signatures of dynamical relaxation. NGC 1883 is located in the
anticentre direction, and exhibits a reddening in the range E(B-V) =
0.23-0.35, depending on the metal abundance. It turns out to be of
intermediate age (1 Gyr old), and is quite distant for an open cluster.
In fact, it is located 4.8 kpc from the Sun, and more than 13 kpc from
the Galactic centre. This results makes NGC 1883 one of the most
peripheral old open clusters, with important consequences for the trend
of the metallicity with distance in the outer Galactic disc.
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=42a068d47524120
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 - 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=42a068d47524120
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 - 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=42a068d47524120
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 - 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=42a068d47524120
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 - 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=42a068d47524120
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 - 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=42a068d47524120
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 - Are the hosts of gamma-ray bursts sub-luminous and blue galaxies?
A1 - Le Floc'h, E.
A1 - Duc, P.-A.
A1 - Mirabel, I. F.
A1 - Sanders, D. B.
A1 - Bosch, G.
A1 - Diaz, R. J.
A1 - Donzelli, C. J.
A1 - Rodrigues, I.
A1 - Courvoisier, T. J.-L.
A1 - Greiner, J.
A1 - Mereghetti, S.
A1 - Melnick, J.
A1 - Maza, J.
A1 - Minniti, D.
JO - Astronomy and Astrophysics
VL - 400
Y1 - 2003/3/1
SP - 499
EP - 510
KW - galaxies: starburst/ galaxies: evolution/ cosmology: observations/ gamma rays: bursts
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...400..499L&db_key=AST&high=42a068d47524120
N2 - We present K-band imaging observations of ten gamma-ray burst (GRB) host
galaxies for which an optical and/or radio afterglow associated with the
GRB event was clearly identified. Data were obtained with the Very Large
Telescope and New Technology Telescope at ESO (Chile), and with the
Gemini-North telescope at Mauna Kea (Hawaii). Adding to our sample nine
other GRB hosts with K-band photometry and determined redshifts
published in the literature, we compare their observed and absolute K
magnitudes as well as their R-K colours with those of other distant
sources detected in various optical, near-infrared, mid-infrared and
submillimeter deep surveys. We find that the GRB host galaxies, most of
them lying at 0.5<~ z la1 .5, exhibit very blue colours, comparable
to those of the faint blue star-forming sources at high redshift. They
are sub-luminous in the K-band, suggesting a low stellar mass content.
We do not find any GRB hosts harbouring R- and K-band properties similar
to those characterizing the luminous infrared/submillimeter sources and
the extremely red starbursts. Should GRBs be regarded as an unbiased
probe of star-forming activity, this lack of luminous and/or reddened
objects among the GRB host sample might reveal that the detection of GRB
optical afterglows is likely biased toward unobscured galaxies. It would
moreover support the idea that a large fraction of the optically-dark
GRBs occur within dust-enshrouded regions of star formation. On the
other hand, our result might also simply reflect intrinsic properties of
GRB host galaxies experiencing a first episode of very massive star
formation and characterized by a rather weak underlying stellar
population. Finally, we compute the absolute B magnitudes for the whole
sample of GRB host galaxies with known redshifts and detected at optical
wavelengths. We find that the latter appear statistically even less
luminous than the faint blue sources which mostly contributed to the
B-band light emitted at high redshift. This indicates that the formation
of GRBs could be favoured in particular systems with very low
luminosities and, therefore, low metallicities. Such an intrinsic bias
toward metal-poor environments would be actually consistent with what
can be expected from the currently-favoured scenario of the
``collapsar''. The forthcoming launch of the SWIFT mission at the end of
2003 will provide a dramatic increase of the number of GRB-selected
sources. A detailed study of the chemical composition of the gas within
this sample of galaxies will thus allow us to further analyse the
potential effect of metallicity in the formation of GRB events.
Based on observations with the Very Large Telescope, obtained at the
European Southern Observatory in Chile under proposal 67.B-0611(A).
Based on observations with the Gemini-North Telescope, obtained at Mauna
Kea (Hawaii) under proposal GN-2001A-Q-58.
Appendix A is only available in electronic form at
http://www.edpsciences.org
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=42a068d47524120
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 - An HI interstellar bubble surrounding WR85 and RCW118
A1 - Vasquez, J.
A1 - Cappa, C.
A1 - McClure-Griffiths, N. M.
JO - Monthly Notices of the Royal Astronomical Society
VL - 362
Y1 - 2005/9/1
SP - 681
EP - 688
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.362..681V&db_key=AST&high=42a068d47528003
N2 - We analyse the distribution of the interstellar matter in the environs
of the Wolf-Rayet star LSS3982 (= WR85, WN6+OB?) linked to the optical
ring nebula RCW118. Our study is based on neutral hydrogen 21-cm line
data belonging to the Southern Galactic Plane Survey (SGPS).
The analysis of the HI data allowed the identification of a neutral
hydrogen interstellar bubble related to WR85 and the 25-arcmin-diameter
ring nebula RCW118. The HI bubble was detected at a systemic velocity of
-21.5 km s-1, corresponding to a kinematical distance of 2.8
+/- 1.1 kpc, compatible with the stellar distance. The neutral structure
is about 25 arcmin in radius or 21 +/- 8 pc, and is expanding at 9 +/- 2
km s-1. The associated ionized and neutral masses amount to
3000 Msolar. The carbon monoxide (CO) emission distribution
depicts a region lacking CO coincident in position and velocity with the
HI structure. The 9.3-arcmin-diameter inner optical nebula appears to be
related to the approaching part of the neutral atomic shell. The HI void
and shell are the neutral gas counterparts of the optical bubble and
have very probably originated in the action of the strong stellar wind
of the central star during the O-type and WR phases on the surrounding
interstellar medium. The HI bubble appears to be in the momentum
conserving stage.
ER -
TY - Journal
T1 - The origin and nature of Neptune-like planets orbiting close to solar type stars
A1 - Brunini, Adrián
A1 - Cionco, Rodolfo G.
JO - Icarus
VL - 177
Y1 - 2005/9/1
SP - 264
EP - 268
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..177..264B&db_key=AST&high=42a068d47528003
N2 - The sample of known exoplanets is strongly biased to masses larger than
the ones of the giant gaseous planets of the Solar System. Recently, the
discovery of two extrasolar planets of considerably lower masses around
the nearby Stars GJ 436 and rho Cancri was reported. They are like our
outermost icy giants, Uranus and Neptune, but in contrast, these new
planets are orbiting at only some hundredth of the Earth Sun distance
from their host stars, raising several new questions about their origin
and constitution. Here we report numerical simulations of planetary
accretion that show, for the first time through N-body integrations that
the formation of compact systems of Neptune-like planets close to the
hosts stars could be a common by-product of planetary formation. We
found a regime of planetary accretion, in which orbital migration
accumulates protoplanets in a narrow region around the inner edge of the
nebula, where they collide each other giving rise to Neptune-like
planets. Our results suggest that, if a protoplanetary solar environment
is common in the Galaxy, the discovery of a vast population of this sort
of `hot cores' should be expected in the near future.
ER -
TY - Journal
T1 - Separating C Stars from Dust in the Central Region of the Seyfert 2 Galaxy NGC 1241
A1 - Dottori, Horacio
A1 - Díaz, Rubén J.
A1 - Carranza, Gustavo
A1 - Lípari, Sebastián
A1 - Santos, João, Jr.
JO - Astrophysical Journal
VL - 628
Y1 - 2005/8/1
SP - L85
EP - L88
KW - Galaxies: Active/ Galaxies: Individual: NGC Number: NGC 1241/ Galaxies: ISM/ Galaxies: Nuclei/ Galaxies: Photometry/ Galaxies: Stellar Content
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...628L..85D&db_key=AST&high=42a068d47528003
N2 - The Seyfert 2 galaxy NGC 1241 presents a 1.5 kpc large circumnuclear
ring (CNR) of star formation embracing a small bar plus leading arms.
Those structures are Paalpha emitters but barely seen in Halpha. It
also presents stellar trailing arms inside the CNR. Gemini and HST
imagery allow the construction of high-resolution (V-H) and
(J-Ks) color maps, as well as a (J-Ks) versus K
color-magnitude diagram of this complex region. The CNR is heavily
obscured in V, but a fairly transparent window appears in the direction
of the nucleus. Nonetheless, the nucleus presents a (J-Ks)
color that is redder than the CNR. The CNR is composed of extremely
young H II regions still enshrouded in their dust cocoons. However, the
nuclear (J-Ks) color cannot be explained in this manner.
Therefore, we propose the contribution of C stars as the most feasible
mechanism for explaining the colors. If the nuclear stellar population
is comparable to that of the Large Magellanic Cloud bar, 500 C stars and
25,000 asymptotic giant branch O-rich stars inside 50 pc may reproduce
the observed colors. C stars release enriched material to the nuclear
environment, probably fueling the central engine of this Seyfert 2
galaxy during the lifetime of stars with masses in the range 2
MsolarCstar<6 Msolar (C-star
phase). The ejected material that remains trapped in the central
potential might also explain the systematically observed increased
strength of the optical CN bands in Seyfert 2 galaxies and is consistent
with the significant contribution of intermediate age stars to the
optical continuum of low-luminosity active galactic nuclei.
ER -
TY - Journal
T1 - H I bubbles surrounding southern optical ring nebulae: Anon (WR 23) and RCW 52
A1 - Cappa, C.
A1 - Niemela, V. S.
A1 - Martín, M. C.
A1 - McClure-Griffiths, N. M.
JO - Astronomy and Astrophysics
VL - 436
Y1 - 2005/6/1
SP - 155
EP - 163
KW - ISM: bubbles/ Hii regions
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...436..155C&db_key=AST&high=42a068d47528003
N2 - We analyze the interstellar medium in the environs of two hot and
massive stars, HD 92809 (=WR 23, WC6) and LSS 1887 (O8V), which ionize
the optical ring nebulae Anon (WR 23) and RCW 52, respectively. Our
analysis is based on neutral hydrogen (Hi) 21 cm line data, which reveal
interstellar bubbles surrounding the massive stars and their optical
ring nebulae. The Hi bubble related to WR 23 is 13.3 pc in radius and is
expanding at 10 km s-1. The associated atomic neutral mass is
830 M_⊙. The Hi structure related to LSS 1887 is about 6.3 pc in
radius, has an expansion velocity of 7 km s-1 and an
associated atomic neutral mass of 100 M_⊙. These Hi features are
the neutral counterparts of the optical ring nebulae and were mainly
created by the action of the stellar winds of the massive stars on their
environs. The dynamical age of the Hi bubble around WR 23
(7×105 yr) suggests that it was created during the WR
phase of stellar evolution. However, the large tangential motions of WR
23 and LSS 1887 suggest that part of the observed optical and Hi
structures may be due to a bow shock. The analysis of the distribution
of emission in the far infrared and in the CO(1-0) molecular line in the
environs of WR 23 and LSS 1887 reveals that there are also infrared and
molecular counterparts of the detected Hi bubbles.
ER -
TY - Journal
T1 - Hilda asteroids among Jupiter family comets
A1 - di Sisto, Romina P.
A1 - Brunini, Adrián
A1 - Dirani, Lorena D.
A1 - Orellana, Rosa B.
JO - Icarus
VL - 174
Y1 - 2005/3/1
SP - 81
EP - 89
KW - Comets/ Asteroids/ Dynamical evolution/ Resonance
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..174...81D&db_key=AST&high=42a068d47528003
N2 - Hilda asteroids and comets are similar from the compositional point of
view. The D-taxonomic class prevailing among Hildas has all the
characteristics found in cometary spectra. Jupiter Family Comets (JFCs)
coming from the trans-neptunian region are under the gravitational
control of Jupiter, making them a dynamically unstable population with a
mean dynamical lifetime of 104 to 105 years. In
contrast, Hilda asteroids residing in the 3:2 mean motion resonance with
Jupiter are a very stable population. But once they escape from the
resonance, they are dynamically controlled by Jupiter, and in this sense
their behavior resembles that of JFC. We performed a numerical
simulation to analyze the dynamical evolution that Hildas follow after
escaping from the resonance, and their contribution to the JFC
population. We found that 8% of the particles leaving the resonance end
up impacting Jupiter. 98.7% of the escaped Hildas live at least 1000
years as a JFC, with a mean lifetime of 1.4×106 years.
In particular, escaped Hildas stay mainly in the region of perihelion
distances greater than 2.5 AU. On the other hand, the number of escaped
Hildas reaching the inner Solar System (q<2.5 AU) is negligible. So,
there are almost no Hilda asteroids among the NEO population. We also
analyzed the possibility that the Shoemaker-Levy 9 were an escaped Hilda
asteroid. In this case, it would be possible to give stronger
constraints to its pre-capture orbital elements.
ER -
TY - Journal
T1 - Methods for computing giant planet formation and evolution
A1 - Benvenuto, O. G.
A1 - Brunini, A.
JO - Monthly Notices of the Royal Astronomical Society
VL - 356
Y1 - 2005/2/1
SP - 1383
EP - 1395
KW - planets and satellites: formation/ galaxies: evolution
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.356.1383B&db_key=AST&high=42a068d47528003
N2 - We present a numerical code for computing all stages of the formation
and evolution of giant planets in the framework of the core instability
mechanism. This code is a non-trivial adaption of the stellar binary
evolution code and is based on a standard Henyey technique. To
investigate the performance of this code we applied it to the
computation of the formation and evolution of a Jupiter mass object from
a half Earth core mass to ages in excess of the age of the Universe.
We also present a new smoothed linear interpolation algorithm devised
especially for the purpose of circumventing some problems found when
some physical data (e.g. opacities, equation of state, etc.) are
introduced into an implicit algorithm like the one employed in this
work.
ER -
TY - Journal
T1 - On The Origin of The High-Perihelion Scattered Disk: The Role of The Kozai Mechanism And Mean Motion Resonances
A1 - Gomes, Rodney S.
A1 - Gallardo, Tabaré
A1 - Fernández, Julio A.
A1 - Brunini, Adrián
JO - Celestial Mechanics and Dynamical Astronomy
VL - 91
Y1 - 2005/1/1
SP - 109
EP - 129
KW - Edgeworth--Kuiper belt/ scattered disk/ Kozai/ comets: dynamics/ Edgeworth&ndash/ Kuiper belt
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005CeMDA..91..109G&db_key=AST&high=42a068d47528003
N2 - We study the transfer process from the scattered disk (SD) to the
high-perihelion scattered disk (HPSD) (defined as the population with
perihelion distances q > 40 AU and semimajor axes a>50 AU) by
means of two different models. One model (Model 1) assumes that SD
objects (SDOs) were formed closer to the Sun and driven outwards by
resonant coupling with the accreting Neptune during the stage of outward
migration (Gomes 2003b, Earth, Moon, Planets 92, 29 42.). The other
model (Model 2) considers the observed population of SDOs plus clones
that try to compensate for observational discovery bias
(Fernández et al. 2004, Icarus , in press). We find that the
Kozai mechanism (coupling between the argument of perihelion,
eccentricity, and inclination), associated with a mean motion resonance
(MMR), is the main responsible for raising both the perihelion distance
and the inclination of SDOs. The highest perihelion distance for a body
of our samples was found to be q = 69.2 AU. This shows that bodies can
be temporarily detached from the planetary region by dynamical
interactions with the planets. This phenomenon is temporary since the
same coupling of Kozai with a MMR will at some point bring the bodies
back to states of lower-q values. However, the dynamical time scale in
high-q states may be very long, up to several Gyr. For Model 1, about
10% of the bodies driven away by Neptune get trapped into the HPSD when
the resonant coupling Kozai-MMR is disrupted by Neptune's
migration. Therefore, Model 1 also supplies a fossil HPSD, whose bodies
remain in non-resonant orbits and thus stable for the age of the solar
system, in addition to the HPSD formed by temporary captures of SDOs
after the giant planets reached their current orbits. We find that about
12 15% of the surviving bodies of our samples are incorporated into
the HPSD after about 4 5 Gyr, and that a large fraction of the
captures occur for up to the 1:8 MMR (a â‹ 120 AU), although we
record captures up to the 1:24 MMR (a ≃ 260 AU). Because of the
Kozai mechanism, HPSD objects have on average inclinations about 25°
50°, which are higher than those of the classical Edgeworth Kuiper
(EK) belt or the SD. Our results suggest that Sedna belongs to a
dynamically distinct population from the HPSD, possibly being a member
of the inner core of the Oort cloud. As regards to 2000 CR105
, it is marginally within the region occupied by HPSD objects in the
parametric planes (q,a) and (a,i), so it is not ruled out that it might
be a member of the HPSD, though it might as well belong to the inner
core.
ER -
TY - Journal
T1 - The scattered disk population as a source of Oort cloud comets: evaluation of its current and past role in populating the Oort cloud
A1 - Fernández, Julio A.
A1 - Gallardo, Tabaré
A1 - Brunini, Adrián
JO - Icarus
VL - 172
Y1 - 2004/12/1
SP - 372
EP - 381
KW - Edgeworth-Kuiper belt/ Scattered disk/ Oort cloud/ dynamics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Icar..172..372F&db_key=AST&high=42a068d47528003
N2 - We have integrated the orbits of the 76 scattered disk objects (SDOs),
discovered through the end of 2002, plus 399 clones for 5 Gyr to study
their dynamical evolution and the probability of falling in one of the
following end states: reaching Jupiter's influence zone, hyperbolic
ejection, or transfer to the Oort cloud. We find that nearly 50% of the
SDOs are transferred to the Oort cloud (i.e., they reach heliocentric
distances greater than 20,000 AU in a barycentric elliptical orbit),
from which about 60% have their perihelia beyond Neptune's orbit
(31 AU1 km incorporated into the Oort cloud is about 5
yr-1, which might be a non-negligible fraction of comet
losses from the Oort cloud (probably around or even above 10%).
Therefore, we conclude that the Oort cloud may have experienced and may
be even experiencing a significant renovation of its population, and
that the trans-neptunian belt---via the scattered disk---may be
the main feeding source.
ER -
TY - Journal
T1 - Catalog of Double Nucleus Disk Galaxies
A1 - Gimeno, Germán N.
A1 - Díaz, Rubén J.
A1 - Carranza, Gustavo J.
JO - Astronomical Journal
VL - 128
Y1 - 2004/7/1
SP - 62
EP - 67
KW - Galaxies: Nuclei/ Galaxies: Peculiar/ Galaxies: Statistics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....128...62G&db_key=AST&high=42a068d47528003
N2 - We have compiled a catalog of disk galaxies that have a double nucleus,
through systematic examination of existing catalogs and publications.
The Catalog of Double Nucleus Disk Galaxies includes 107 objects,
together with their basic data. The aim of the catalog is to provide a
more systematic and homogeneous basis for the study of the relevance of
galaxy interactions and minor mergers in the formation of these double
nuclei. We have also investigated possible correlations between
geometric and photometric parameters of the double nuclei and their host
galaxies. The preliminary results indicate the presence of several
significant correlations that should be considered in any theoretical
scenario describing minor mergers and disk galaxy evolution.
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=42a068d47528003
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 - 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=42a068d47528003
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=42a068d47528003
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 Scattered Disk Population and the Oort Cloud
A1 - Fernández, Julio A.
A1 - Gallardo, Tabaré
A1 - Brunini, Adrián
JO - Earth Moon and Planets
VL - 92
Y1 - 2003/6/1
SP - 43
EP - 48
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003EM%26P...92...43F&db_key=AST&high=42a068d47528003
N2 - The trans-Neptunian belt has been subject to a strong depletion that has
reduced its primordial population by a factor of one hundred over the
solar system's age. One by-product of such a depletion process is the
existence of a scattered disk population in transit from the belt to
other places, such as the Jupiter zone, the Oort cloud or interstellar
space. We have integrated the orbits of the scattered disk objects
(SDOs) so far discovered by 2500 Myr to study their dynamical time
scales and the probability of falling in each of the end states
mentioned above, paying special attention to their contribution to the
Oort cloud. We found that their dynamical half-time is close to 2.5 Gyr
and that about one third of the SDOs end up in the Oort cloud.
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=42a068d47528003
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 - PKS 1622-253: A Weakly Accreting, Powerful Gamma-Ray Source
A1 - Punsly, Brian
A1 - Rodríguez, Luis F.
A1 - Tingay, Steven J.
A1 - Cellone, Sergio A.
JO - Astrophysical Journal
VL - 633
Y1 - 2005/11/1
SP - L93
EP - L96
KW - Accretion/ Accretion Disks/ Black Hole Physics/ Galaxies: Active/ Galaxies: Jets/ Galaxies: Quasars: General/ Galaxies: Quasars: Individual: Alphanumeric: PKS 1622-253
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...633L..93P&db_key=AST&high=42a068d47531851
N2 - We discuss new deep radio observations of PKS 1622-253 and their
implications for the energetics of the central engine that powers this
strong high-energy gamma-ray source. Combining archival infrared and
optical measurements with new millimeter observations, we show that even
though the accretion flow in PKS 1622-253 is underluminous by quasar
standards, a powerful superluminal jet is launched with a higher kinetic
luminosity than most EGRET blazars. Only a few percent of the total jet
kinetic luminosity is required to power even the most powerful gamma-ray
flares that are observed. The implication is that a high-accretion
system is not required in order to power the strongest high-energy
gamma-ray sources.
ER -
TY - Journal
T1 - On the evolutionary status of Be stars. I. Field Be stars near the Sun
A1 - Zorec, J.
A1 - Frémat, Y.
A1 - Cidale, L.
JO - Astronomy and Astrophysics
VL - 441
Y1 - 2005/10/1
SP - 235
EP - 248
KW - stars: emission-line/ Be/ stars: evolution/ stars: rotation/ stars: fundamental parameters (classification/ colors/ luminosities/ masses/ radii/ temperatures/ etc.)
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...441..235Z&db_key=AST&high=42a068d47531851
N2 - A sample of 97 galactic field Be stars were studied by taking into
account the effects induced by the fast rotation on their fundamental
parameters. All program stars were observed in the BCD
spectrophotometric system in order to minimize the perturbations
produced by the circumstellar environment on the spectral photospheric
signatures. This is one of the first attempts at determining stellar
masses and ages by simultaneously using model atmospheres and
evolutionary tracks, both calculated for rotating objects. The stellar
ages (tau) normalized to the respective inferred time that each
rotating star can spend in the main sequence phase (tau_MS) reveal a
mass-dependent trend. This trend shows that: a) there are Be stars
spread over the whole interval 0 î«¥ tau/tau_MS î«¥ 1 of the
main sequence evolutionary phase; b) the distribution of points in the
(tau/tauMS,M/M⊙) diagram indicates that
in massive stars (M  12~M⊙) the Be phenomenon is
present at smaller tau/tau_MS age ratios than for less massive stars
(M  12~M⊙). This distribution can be due to: i)
higher mass-loss rates in massive objets, which can act to reduce the
surface fast rotation; ii) circulation time scales to transport angular
momentum from the core to the surface, which are longer the lower the
stellar mass.
ER -
TY - Journal
T1 - Outflowing disk formation in B[e] supergiants due to rotation and bi-stability in radiation driven winds
A1 - Curé, M.
A1 - Rial, D. F.
A1 - Cidale, L.
JO - Astronomy and Astrophysics
VL - 437
Y1 - 2005/7/1
SP - 929
EP - 933
KW - stars: early-type/ stars: mass-loss/ stars: rotation/ stars: winds/ outflows
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...437..929C&db_key=AST&high=42a068d47531851
N2 - The effects of rapid rotation and bi-stability upon the density contrast
between the equatorial and polar directions of a B[e] supergiant are
re-investigated. Based on a new slow solution for different high
rotational radiation-driven winds and the fact that bi-stability allows
a change in the line-force parameters (alpha, k, and delta), the
equatorial densities are about 10^2-104 times higher than the
polar ones. These values are in qualitative agreement with the
observations.
ER -
TY - Journal
T1 - Revealing the nature of double-periodic blue variables in the Magellanic Clouds
A1 - Mennickent, R. E.
A1 - Cidale, L.
A1 - Díaz, M.
A1 - Pietrzynski, G.
A1 - Gieren, W.
A1 - Sabogal, B.
JO - Monthly Notices of the Royal Astronomical Society
VL - 357
Y1 - 2005/3/1
SP - 1219
EP - 1230
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.357.1219M&db_key=AST&high=42a068d47531851
N2 - We present the first spectroscopic data for a sample of the recently
discovered blue double-periodic variables in the Magellanic Clouds. The
optical spectrum of these objects is dominated by Balmer and helium
absorption lines and a continuum with a blue or sometimes flat slope.
Spectral classification yields B spectral types and luminosity classes
mostly of type III. However, the Hbeta absorption line is weaker than
expected for the spectral classification in most objects. For two
objects, OGLE 05060009-6855025 and OGLE 05195898-6917013 we obtained
time-resolved spectroscopy, finding radial velocity variations
consistent with binarity. Phasing the short-term photometric variability
of these two systems with their spectroscopic ephemeris, we find that
they can be interpreted as ellipsoidal variations of the brighter
component in a close binary system. From the analysis of their
short-term light curves and radial velocities, we estimate that the
cooler component could be a B-type dwarf. Our findings support the
hypothesis that double-periodic variables are close binary systems
consisting of two B-type stars. The shorter periodicity in non-eclipsing
systems should be the ellipsoidal variation of the more evolved
component. Regarding the long-term periodicity, we find their origin in
or around the brighter star, as the oscillations virtually disappear at
primary eclipse. Their nature remains unknown, at the present time. We
also report the discovery of three (two of them eclipsing) new
double-periodic variables in the Large Magellanic Cloud. One of them
shows a shortening of the long-term period by approximately 20 per cent
in a couple of cycles, which coincides with an increase of the maximum
oscillation brightness.
ER -
TY - Journal
T1 - The low-luminosity galaxy population in the NGC5044 Group
A1 - Cellone, Sergio A.
A1 - Buzzoni, Alberto
JO - Monthly Notices of the Royal Astronomical Society
VL - 356
Y1 - 2005/1/1
SP - 41
EP - 53
KW - galaxies: clusters: individual: NGC 5044 Group/ galaxies: dwarf/ galaxies: kinematics and dynamics/ galaxies: photometry
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.356...41C&db_key=AST&high=42a068d47531851
N2 - We present multicolour imaging for a sample of 33 dwarf and
intermediate-luminosity galaxies in the field of the NGC5044 Group,
complemented with mid-resolution spectroscopy for a subsample of 13
objects. With these data, a revised membership and morphological
classification is made for the galaxies in the sample. We were able to
confirm all but one of the `definite members' included in the
spectroscopic subsample, galaxies which were originally classified based
on morphological criteria. An important fraction of background galaxies,
however, is probably present among `likely' and `possible' members.
The presence of a nucleus could be detected in just five out of the nine
galaxies originally classified as dE,N, confirming the intrinsic
difficulty of photographic-plate morphological classification for this
kind of object. Our deep surface photometry provided clear evidence for
disc structure in at least three galaxies previously catalogued as dE or
dS0. Their transition-type properties are also evident from the
colour-magnitude diagram, where they lie near the late-type galaxy
locus, suggesting an evolutionary connection between a parent
disc-galaxy population and at least some present-day dEs.
Six new dSph candidates were also found, most of them at small projected
distances from NGC5044, the central galaxy of the group.
The NGC5044 Group appears clearly defined in redshift space, with a mean
heliocentric radial velocity of r>= 2461 +/- 84km
s-1 (z= 0.0082), and a moderate dispersion of
sigmavr= 431 km s-1. Our kinematical
data show no luminosity segregation for early-type galaxies: both dwarf
and bright E/S0 systems show very similar velocity distributions
(sigmavr~ 290 km s-1). This is in
contrast to late-type galaxies, which seem to display a broader
distribution (sigmavr~ 680 km s-1).
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=42a068d47531851
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 - 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=42a068d47531851
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 - 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=42a068d47531851
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 - 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=42a068d47531851
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 - NP Pavonis : Differential Corrections Analysis of the UBV Observations
A1 - Cerruti, M. A.
JO - Revista Mexicana de Astronomia y Astrofisica
VL - 39
Y1 - 2003/1/1
SP - 141
EP - 148
KW - Binaries: close/ Binaries: eclipsing/ Stars: individual (NP)
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003RMxAA..39..141C&db_key=AST&high=42a068d47531851
N2 - The first photoelectric analysis of the NPbinary system based on U, B,
and V light curves and modeled using the Wilson & Devinney approach,
is presented. The light curves are defined by 3861 individual
observations. The components and the orbit appears to be in general
stable. The primary, more massive, more luminous is the greater
component, eclipsed at primary minimum and is detached from its Roche
lobe (94%). The secondary nearly fills its Roche lobe (99%) and has a
temperature difference of Delta = - 1330^oK. The absolute elements were
obtained supposing that the primary follows the mass-luminosity
relation.
ER -
TY - Journal
T1 - Washington photometry of open cluster giants: two moderately metal-poor anticentre clusters
A1 - Celeste Parisi, M.
A1 - Clariá, Juan J.
A1 - Piatti, Andrés E.
A1 - Geisler, Douglas
JO - Monthly Notices of the Royal Astronomical Society
VL - 363
Y1 - 2005/11/1
SP - 1247
EP - 1256
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.363.1247C&db_key=AST&high=42a068d47505366
N2 - New photometric data in the Washington system are presented for red
giant candidates in NGC 1817 and 2251, two open clusters located towards
the Galactic anticentre direction. In the case of NGC 2251, the
Washington data are supplemented with new UBV and David Dunlap
Observatory (DDO) photoelectric photometry. Published radial velocities
are used to separate field stars from cluster giants. The photometric
data yield an effective temperature and metal abundance for each cluster
member. Five independent Washington abundance indices yield mean
metallicities of [Fe/H]= 0.25 +/- 0.04 for NGC 1817 and 2251,
respectively. From combined BV and DDO data, we also derive E(B-V) =
0.21 +/- 0.03 and [Fe/H]DDO=-0.14 +/- 0.05 for NGC 2251. Both
objects are then found to be on the metal-poor side of the distribution
of open clusters, their metallicities being compatible with the
existence of a radial abundance gradient in the disc. Using the WEBDA
Open Cluster data base and the available literature, we re-examined the
overall properties of a sample of 30 clusters located towards the
Galactic anticentre with the distances, ages and metallicities
available. This cluster sample presents no evidence of an abundance
gradient perpendicular to the Galactic plane, nor is an age-metallicity
relation found. However, a radial abundance gradient of -0.093 dex
kpc-1 is derived over a Galactocentric distance of 14 kpc, a
gradient which is in keeping with most recent determinations. This value
practically does not change when all clusters with basic parameters
known up to this date are considered.
ER -
TY - Journal
T1 - Characterization of intensity and spatial variations along coronal loops. II. A TRACE case study
A1 - Borgazzi, A.
A1 - Costa, A.
JO - Astronomy and Astrophysics
VL - 441
Y1 - 2005/10/1
SP - 327
EP - 335
KW - Sun: corona/ waves/ Sun: magnetic fields/ instabilities
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...441..327B&db_key=AST&high=42a068d47505366
N2 - We describe dynamical features and evolutionary characteristics of
brightening coronal loops. We describe intensity variations, both in
space and time, along a coarse grain loop structure, confirming high
speed velocity scenarios. We apply the method to TRACE space-born images
that show a compound of several magnetic threads. MICA ground-based
images display a unique non-resolved loop structure. We confirm that a
coherent behavior of the intensity along neighboring magnetic tubes
occurs, i.e. we obtain a similar pattern from both telescopes: each has
two branches, suggesting the sliding down of plasma in both directions
from a given position on the loop structure. The apparent sliding down
occurs in approximately 12 min. After the first appearance, TRACE
registers two reiterations of the phenomenon suggesting a wave-based
explanation. The feasibility of wave-based and flow-based models is
analyzed. In either case, in order to explain the coherent coronal
behavior the scenario of apparently non-interacting coronal threads
requires theoretical explanations that consider uniform chromospheric
conditions covering the footpoints of all the related magnetic tubes. We
suggest a characteristic longitude of coherence.
ER -
TY - Journal
T1 - The WEBT campaign to observe AO 0235+16 in the 2003-2004 observing season. Results from radio-to-optical monitoring and XMM-Newton observations
A1 - Raiteri, C. M.
A1 - Villata, M.
A1 - Ibrahimov, M. A.
A1 - Larionov, V. M.
A1 - Kadler, M.
A1 - Aller, H. D.
A1 - Aller, M. F.
A1 - Kovalev, Y. Y.
A1 - Lanteri, L.
A1 - Nilsson, K.
A1 - Papadakis, I. E.
A1 - Pursimo, T.
A1 - Romero, G. E.
A1 - Teräsranta, H.
A1 - Tornikoski, M.
A1 - Arkharov, A. A.
A1 - Barnaby, D.
A1 - Berdyugin, A.
A1 - Böttcher, M.
A1 - Byckling, K.
A1 - Carini, M. T.
A1 - Carosati, D.
A1 - Cellone, S. A.
A1 - Ciprini, S.
A1 - Combi, J. A.
A1 - Crapanzano, S.
A1 - Crowe, R.
A1 - di Paola, A.
A1 - Dolci, M.
A1 - Fuhrmann, L.
A1 - Gu, M.
A1 - Hagen-Thorn, V. A.
A1 - Hakala, P.
A1 - Impellizzeri, V.
A1 - Jorstad, S.
A1 - Kerp, J.
A1 - Kimeridze, G. N.
A1 - Kovalev, Yu. A.
A1 - Kraus, A.
A1 - Krichbaum, T. P.
A1 - Kurtanidze, O. M.
A1 - Lähteenmäki, A.
A1 - Lindfors, E.
A1 - Mingaliev, M. G.
A1 - Nesci, R.
A1 - Nikolashvili, M. G.
A1 - Ohlert, J.
A1 - Orio, M.
A1 - Ostorero, L.
A1 - Pasanen, M.
A1 - Pati, A.
A1 - Poteet, C.
A1 - Ros, E.
A1 - Ros, J. A.
A1 - Shastri, P.
A1 - Sigua, L. A.
A1 - Sillanpää, A.
A1 - Smith, N.
A1 - Takalo, L. O.
A1 - Tosti, G.
A1 - Vasileva, A.
A1 - Wagner, S. J.
A1 - Walters, R.
A1 - Webb, J. R.
A1 - Wills, W.
A1 - Witzel, A.
A1 - Xilouris, E.
JO - Astronomy and Astrophysics
VL - 438
Y1 - 2005/7/1
SP - 39
EP - 53
KW - galaxies: active/ BL Lacertae objects: general/ BL Lacertae objects: individual: AO 0235+16
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...438...39R&db_key=AST&high=42a068d47505366
N2 - A multiwavelength campaign to observe the BL Lac object AO
0235+16 (z=0.94) was set up by the Whole Earth Blazar
Telescope (WEBT) collaboration during the observing seasons 2003-2004
and 2004-2005, involving radio, near-IR and optical photometric
monitoring, VLBA monitoring, optical spectral monitoring, and three
pointings by the XMM-Newton satellite. Here we report on the results of
the first season, which involved the participation of 24 optical and
near-IR telescopes and 4 radio telescopes, as well as the first
XMM-Newton pointing, which occurred on January 18-19, 2004. Unpublished
data from previous epochs were also collected (from 5 optical-NIR and 3
radio telescopes), in order to fill the gap between the end of the
period presented in Raiteri et al. (2001) and the start of the WEBT
campaign. The contribution of the southern AGN, 2 arcsec distant from
the source, is taken into account. It is found to especially affect the
blue part of the optical spectrum when the source is faint. In the
optical and near-IR the source has been very active in the last 3 years,
although it has been rather faint most of the time, with noticeable
variations of more than a magnitude over a few days. In contrast, in the
radio bands it appears to have been ``quiescent'' since early
2000. The major radio (and optical) outburst predicted to peak around
February-March 2004 (with a six month uncertainty) has not occurred yet.
When comparing our results with the historical light curves, two
different behaviours seem to characterize the optical outbursts: only
the major events present a radio counterpart. The X-ray spectra obtained
by the three EPIC detectors are well fitted by a power law with
extra-absorption at z=0.524; the energy index in the 0.2-10 keV range is
well constrained: alpha=0.645 ± 0.028 and the 1 keV flux
density is 0.311 ± 0.008~mu Jy. The analysis of the X-ray light
curves reveals that no significant variations occurred during the
pointing. In contrast, simultaneous dense radio monitoring with the 100
m telescope at Effelsberg shows a ~2-3% flux decrease in 6-7 h, which,
if intrinsic, would imply a brightness temperature well above the
Compton limit and hence a lower limit to the Doppler factor delta
î«¢ 46. We construct the broad-band spectral energy distribution of
January 18-19, 2004 with simultaneous radio data from Effelsberg,
optical data from the Nordic Optical Telescope (NOT), optical-UV data
from the Optical Monitor onboard XMM-Newton, and X-ray data by the EPIC
instruments. Particular care is taken to correct data for extinction due
to both the Milky Way and the z=0.524 absorber. The resulting SED
suggests the existence of a bump in the UV spectral region.
ER -
TY - Journal
T1 - Exploring the INTEGRAL Sources in Search for New Microquasars
A1 - Ribó, M.
A1 - Combi, J. A.
A1 - Mirabel, I. F.
JO - Chinese Journal of Astronony and Astrophysics
VL - 5
Y1 - 2005/6/1
SP - 1
EP - 6
KW - X-rays: binaries/ X-rays: galaxies/ X-rays: individual: (AX J1639.0-4642/ IGR J16393-4643/ IGR J18027-1455/ IGR J21247+5058)
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ChJAA...5S...1R&db_key=AST&high=42a068d47505366
N2 - Here we present a search for new microquasars among the sources detected
with the INTEGRAL satellite (IGR sources). We focus on radio emitting
IGR sources and report the discovery of two new probable extragalactic
sources behind the galactic plane, as well as the detection at higher
energies of the ASCA source AX J1639.0-4642, probably a new microquasar
in the Galaxy and coincident with a high-energy gamma-ray emitting EGRET
source.
ER -
TY - Journal
T1 - On the Nature of the Unidentified X-ray/gamma-ray Sources Igr J18027 1455 and Igr J21247+5058
A1 - Combi, J. A.
A1 - Ribó, M.
A1 - Mirabel, I. F.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
SP - 385
EP - 391
KW - X-ray:galaxies/ radio continuum: galaxies/ infrared: galaxies
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297..385C&db_key=AST&high=42a068d47505366
N2 - We present a multiwavelength study of the environment of the
unidentified X-ray/gamma-ray sources IGR J18027 1455 and IGR J21247 +
5058, recently discovered by the IBIS/ISGRI instrument, onboard the
INTEGRAL satellite. The main properties of the sources found inside
their position error circles, give us clues about the nature of these
high-energy sources.
ER -
TY - Journal
T1 - Identifying Variable gamma-ray Sources Through Radio Observations
A1 - Paredes, Josep M.
A1 - Martí, J.
A1 - Torres, D. F.
A1 - Romero, G. E.
A1 - Combi, J. A.
A1 - Bosch-Ramon, V.
A1 - García-Sáanchez, J.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
SP - 223
EP - 233
KW - gamma-ray sources/ radio sources/ microquasars/ microblazars/ &gamma/ -ray sources
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297..223P&db_key=AST&high=42a068d47505366
N2 - We present preliminary results of a campaign undertaken with different
radio interferometers to observe a sample of the most variable
unidentified EGRET sources. We expect to detect which of the possible
counterparts of the gamma-ray sources (any of the radio emitters in
the field) varies in time with similar timescales as the gamma-ray
variation. If the gamma-rays are produced in a jet-like source, as we
have modelled theoretically, synchrotron emission is also expected at
radio wavelengths. Such radio emission should appear variable in time
and correlated with the gamma-ray variability.
ER -
TY - Journal
T1 - Towards a Population of HMXB/NS Microquasars as Counterparts of Low-Latitude Unidentified EGRET Sources
A1 - Ribó, M.
A1 - Combi, J. A.
A1 - Mirabel, I. F.
JO - Astrophysics and Space Science
VL - 297
Y1 - 2005/6/1
SP - 143
EP - 154
KW - gamma-ray sources/ X-ray binaries/ microquasars/ &gamma/ -ray sources
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Ap%26SS.297..143R&db_key=AST&high=42a068d47505366
N2 - The discovery of the microquasar LS 5039 well within the 95% confidence
contour of the Unidentified EGRET Source (UES) 3EG J1824-1514 was
a major step towards the possible association between microquasars (MQs)
and UESs. The recent discovery of precessing relativistic radio jets in
LS I +61 303, a source associated for long time with 2CG 135+01 and with
the UES 3EG J0241+6103, has given further support to this idea. Finally,
the very recently proposed association between the microquasar candidate
AX J1639.0-4642 and the UES 3EG J1639-4702 points towards a
population of High Mass X-ray Binary (HMXB)/Neutron Star (NS)
microquasars as counterparts of low-latitude unidentified EGRET sources.
ER -
TY - Journal
T1 - G337.2+0.1: A new X-ray supernova remnant?.
A1 - Combi, J. A.
A1 - Benaglia, P.
A1 - Romero, G. E.
A1 - Sugizaki, M.
JO - Astronomy and Astrophysics
VL - 431
Y1 - 2005/2/1
SP - L9
EP - L12
KW - X-ray: individuals: AX J1635.9-4719
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...431L...9C&db_key=AST&high=42a068d47505366
N2 - We present evidence supporting a SNR origin for the radio source
G337.2+0.1, which was discovered along the line of
sight to the Norma spiral arm in the MOST 843-MHz radio survey. The
radio source is spatially superposed to the unidentified ASCA source
AX J1635.9-4719. An analysis of this latter source
reveals that its X-ray spectrum, extended nature, and non-variable flux
are consistent with what is expected for a SNR. In addition, we have
used HI-line observations of the region to look for any effect of the
presumed remnant on the ISM. We have found a well-defined minimum
centered at the position of the radio source in the velocity range of
~ -25 to -19 km s-1. This feature appears as a sharp
absorption dip in the spectrum that might be produced when the continuum
emission from the SNR candidate is absorbed by foreground gas. Hence we
have used it to constrain the distance to the source, which seems to be
a young (age ~ a few 103 yr) and distant (d~14 kpc)
SNR. G337.2+0.1 and AX
J1635.9-4719 would be the radio/X-ray manifestations of this
remnant.
ER -
TY - Journal
T1 - Photometric and spectroscopic study of low mass embedded star clusters in reflection nebulae
A1 - Soares, J. B.
A1 - Bica, E.
A1 - Ahumada, A. V.
A1 - Clariá, J. J.
JO - Astronomy and Astrophysics
VL - 430
Y1 - 2005/2/1
SP - 987
EP - 996
KW - open clusters and associations: individual: GGD 20/ open clusters and associations: individual: vdBH-RN
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...430..987S&db_key=AST&high=42a068d47505366
N2 - An analysis of the candidate embedded stellar systems in the reflection
nebulae vdBH-RN 26, vdBH-RN} 38, vdBH-RN} 53a, GGD 20, ESO 95-RN 18 and
NGC 6595 is presented. Optical spectroscopic data from CASLEO
(Argentina) in conjunction with near infrared photometry from the 2MASS
Point Source Catalogue were employed. The analysis is based on source
surface density, colour-colour and colour-magnitude diagrams together
with theoretical pre-main sequence isochrones. We take into account the
field population affecting the analysis by carrying out a statistical
subtraction. The fundamental parameters for the stellar systems were
derived. The resulting ages are in the range 1-4 Myr and the objects are
dominated by pre-main sequence stars. The observed masses locked in the
clusters are less than 25 M⊙. The studied systems have
no stars of spectral types earlier than B, indicating that star clusters
do not necessarily evolve through an HII region phase. The relatively
small locked mass combined with the fact that they are not numerous in
catalogues suggests that these low mass clusters are not important
donors of stars to the field populations.
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 - Multicolor Photometry of Red Giant Candidates in the Southern Open Cluster NGC 2447
A1 - Clariá, J. J.
A1 - Piatti, A. E.
A1 - Lapasset, E.
A1 - Parisi, M. C.
JO - Baltic Astronomy
VL - 14
Y1 - 2005/1/1
SP - 301
EP - 311
KW - methods: observational/ techniques: photometric: UBV system/ DDO system/ Washington system/ open clusters: metal abundance
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005BaltA..14..301C&db_key=AST&high=42a068d47505366
N2 - Photoelectric photometry in the UBV, DDO and Washington systems is
presented for 14 late-type giant candidates of the southern open cluster
NGC 2447. By applying two independent photometric criteria, nine stars
are found to have a high probability of being cluster giants. The
photometric membership results are in good agreement with those derived
from published Coravel radial velocities. The mean interstellar
reddening EB-V = 0.05±0.04 has been derived from the
confirmed cluster giants. NGC 2447 has a mean ultraviolet excess
= 0.01±0.02 (sigma n) with
respect to solar composition K giants, and a mean cyanogen anomaly
= 0.01±0.02 (sigma n), both
implying a small metal deficiency ([Fe/H] ≃ -0.1). Five
independent Washington abundance indices yield a mean cluster
metallicity of [Fe/H] = -0.09±0.06, in agreement with the two
previous estimates. Therefore, NGC 2447 is found to be slightly
metal-poor.
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=42a068d47505366
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 - 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=42a068d47505366
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=42a068d47505366
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 - Red giants in open clusters. XI. Membership, duplicity, and structure of NGC 2477
A1 - Eigenbrod, A.
A1 - Mermilliod, J.-C.
A1 - Clariá, J. J.
A1 - Andersen, J.
A1 - Mayor, M.
JO - Astronomy and Astrophysics
VL - 423
Y1 - 2004/8/1
SP - 189
EP - 197
KW - stars: binaries: spectroscopic/ techniques: radial velocities/ star: late-type/ Galaxy: open clusters and associations: individual: NGC 2477
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...423..189E&db_key=AST&high=42a068d47505366
N2 - New, accurate radial velocities and photoelectric UBV photometry of 83
red-giant candidates in the field of the rich, intermediate-age open
cluster NGC 2477 ([Fe/H]= -0.05, age ≃1 Gyr)
are presented and discussed. From 49 constant-velocity members we find a
mean cluster velocity of +7.32±0.13 km s-1 and confirm
the membership of 76 of the stars. Among the cluster members, we
identify 26 definite and 1 probable spectroscopic binaries and determine
orbits for 13 of these systems, with periods ranging from 40 to 4578
days. The binary frequency is thus rather high (27/76 = 36%). The
observed internal radial velocity dispersion of the cluster, as
determined from the single member stars, is 0.93 km s-1,
corrected for the small average observational error of 0.22 km
s-1. Fitting King-type models to the observed stellar density
distribution and velocity dispersion, and assuming a distance of 1.25
kpc, we find the core and tidal radii of NGC 2477 to
be 1.8 and 8.1 pc, respectively, and estimate that the mass of cluster
stars down to V = 17, corresponding to ~1 M⊙, is at
least 5400 M⊙. The substantial differential reddening of
NGC 2477 requires a more detailed study before
definitive isochrone fits can be made.
Based on observations collected with the Danish 1.54-m and ESO 1-m
telescopes at the European Southern Observatory, La Silla, Chile, and
with the University of Toronto 0.6-m telescope at Las Campanas
Observatory, Chile.
Full 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/423/189
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=42a068d47505366
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 - 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=42a068d47505366
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 - Did EGRET detect distant supernova remnants?
A1 - Torres, Diego F.
A1 - Romero, Gustavo E.
A1 - Dame, Thomas M.
A1 - Combi, Jorge A.
A1 - Butt, Yousaf M.
JO - Advances in Space Research
VL - 33
Y1 - 2004/1/1
SP - 450
EP - 455
KW - Supernova remnants/ EGRET/ Gamma ray source
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AdSpR..33..450T&db_key=AST&high=42a068d47505366
N2 - It might be thought that supernova remnants (SNRs) more distant than a
few kiloparsec from Earth could not have been detected by the
high-energy gamma-ray experiment EGRET on board of NASA's Compton
Gamma-Ray Observatory. This work analyzes the observational status of
this statement in the light of new CO studies of SNRs.
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=42a068d47505366
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 - On the calibration of the COBE/IRAS dust emission reddening maps
A1 - Dutra, C. M.
A1 - Ahumada, A. V.
A1 - Clariá, J. J.
A1 - Bica, E.
A1 - Barbuy, B.
JO - Astronomy and Astrophysics
VL - 408
Y1 - 2003/9/1
SP - 287
EP - 295
KW - ISM: dust/ extinction/ Galaxy: general/ galaxies: ISM
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...408..287D&db_key=AST&high=42a068d47505366
N2 - In this work we study the spectral properties (3600-6800 Å) of the
nuclear region of early-type galaxies at low (|b|<25deg),
intermediate (including surroundings of the Magellanic Clouds) and high
(South Polar Cap) Galactic latitudes. We determine the E(B-V) reddening
values of the galaxies by matching their continuum distribution with
respect to those of reddening-free spectral galaxy templates with
similar stellar populations. We also compare the spectroscopic reddening
value of each galaxy with that derived from 100 mu m dust emission
(E(B-V)FIR) in its line of sight, and we find that there is
agreement up to E(B-V)=0.25. Beyond this limit E(B-V)FIR
values are higher. Taking into account the data up to E(B-V) ~ 0.7, we
derive a calibration factor of 0.016 between the spectroscopic E(B-V)
values and Schlegel et al.'s (\cite{Schlegel1998}) opacities. By
combining this result with an AK extinction map built within
ten degrees of the Galactic centre using Bulge giants as probes (Dutra
et al. \cite{Dutra2003}), we extended the calibration of dust emission
reddening maps to low Galactic latitudes down to |b|=4deg and
E(B-V)= 1.6 (AV ~ 5). According to this new calibration, a
multiplicative factor of ~0.75 must be applied to the COBE/IRAS dust
emission reddening maps.
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 Pata,
Córdoba and San Juan, Argentina.
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=42a068d47505366
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 - 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=42a068d47505366
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 - 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=42a068d47505366
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 - Ruprecht 3: An old star cluster remnant?
A1 - Pavani, D. B.
A1 - Bica, E.
A1 - Ahumada, A. V.
A1 - Clariá, J. J.
JO - Astronomy and Astrophysics
VL - 399
Y1 - 2003/2/1
SP - 113
EP - 120
KW - Galaxy: open clusters and stellar associations: general/ open clusters and associations: individual: Ruprecht 3/ methods: observational/ techniques: spectroscopic
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...399..113P&db_key=AST&high=42a068d47505366
N2 - 2MASS J and H photometry and integrated spectroscopy are employed to
study the nature of the poorly populated compact concentration of stars
Ruprecht 3, which was previously catalogued as an open cluster. The
integrated spectrum remarkably resembles that of a moderately metal-rich
globular cluster. The distribution of the object stars in the
colour-magnitude diagram is compatible with that of a 1.5 +/- 0.5 Gyr
open cluster or older, depending on whether the bluer stars are
interpreted as turnoff stars or blue stragglers, respectively. We derive
for the object a distance from the Sun dsun = 0.72
+0.04-0.03 kpc and a colour excess E(B-V) = 0.04.
Although a globular cluster remnant cannot be ruled out, the integrated
spectrum resemblance to that of a globular cluster probably reflects a
stochastic effect owing to the few brighter stars. The structural and
photometric properties of Ruprecht 3 are compatible with what would be
expected for an intermediate-age open cluster remnant.
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 - 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=42a068d47505366
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 - A multi-frequency study of the spectral index distribution in the SNR CTB 80
A1 - Castelletti, G.
A1 - Dubner, G.
JO - Astronomy and Astrophysics
VL - 440
Y1 - 2005/9/1
SP - 171
EP - 177
KW - ISM: individual objects: CTB 80/ pulsar: individual: PSR B1951+32/ ISM: supernova remnants/ radio continuum: ISM
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...440..171C&db_key=AST&high=42a068d47507410
N2 - We have conducted a study at radio wavelengths of the spectral behaviour
of the supernova remnant (SNR) CTB 80. Based on an homogenised data set
of integrated flux densities, we calculated for the whole SNR a radio
index alpha = -0.36 ± 0.02 . The shape of the global spectrum
suggests absorption by ionized gas in the interstellar medium (ISM)
along the line of sight. Spatial spectral variations across the SNR are
investigated based on high-angular resolution data at 240, 324, 610, and
1380 MHz using different techniques. The three extended arms associated
with this SNR show a clear indication of spectral steepening when moving
outwards from the central nebula, with variations of up to Delta
alpha ~ - 0.9 . However, while the spectral steepening is smooth
along the eastern arm, the northern and soutwestern arms include locally
flatter structures, which in all cases coincide with radio, IR and
optical emission enhancements. We interpret this spectral property as
the result of the combination of two different particle populations:
aging relativistic electrons injected by PSR B1951+32 and particles
accelerated at the sites where the SNR shock front encounters
interstellar gas inhomogeneities. Concerning the central nebula, the
angular resolution of the available database does not permit a detailed
spectral study of the core region, i.e. the 45'' region around PSR
B1951+32, where we can only confirm an average spectral index alpha =
0.0 . The surrounding 8' plateau nebula has an < alpha >~ -
0.25, with a peak of alpha ~ - 0.29 coincident with a secondary
maximun located at the termination of a twisted filament that trails to
the east, behind the pulsar.
ER -
TY - Journal
T1 - Hall effect in incompressible magnetic reconnection
A1 - Morales, Laura F.
A1 - Dasso, Sergio
A1 - Gómez, Daniel O.
JO - Journal of Geophysical Research (Space Physics)
VL - 110
Y1 - 2005/4/1
SP - 04204
KW - Magnetospheric Physics: Magnetic reconnection (7526/ 7835)/ Magnetospheric Physics: Magnetopause and boundary layers/ Magnetospheric Physics: Numerical modeling/ Magnetospheric Physics: Solar wind/magnetosphere interactions/ Space Plasma Physics: Magnetic reconnection (2723/ 7526)
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005JGRA..11004204M&db_key=AST&high=42a068d47507410
N2 - Theoretical models of magnetic reconnection have been traditionally
developed within the framework of magnetohydrodynamics (MHD). However,
in low-density astrophysical plasmas like those found in the
magnetopause and the magnetotail, kinetic effects such as the Hall
current are expected to play a significant role. We present results from
externally driven magnetic reconnection simulations, within the
framework of incompressible Hall MHD in 2 1/2 dimensions. We evaluate
the relevance of the Hall current in the reconnection process by
performing a set of simulations with different values of the Hall
parameter. We compute the corresponding reconnection rates as a function
of time and explore the spatial structure of the fields in the
surroundings of the diffusion region.
ER -
TY - Journal
T1 - Photometric Observations of Southern Abell Clusters Redshifts Survey Clusters: Galaxy Luminosity Profiles
A1 - Coenda, Valeria
A1 - Donzelli, Carlos José
A1 - Muriel, Hernan
A1 - Quintana, Hernan
A1 - Infante, Leopoldo
A1 - Lambas, Diego García
JO - Astronomical Journal
VL - 129
Y1 - 2005/3/1
SP - 1237
EP - 1248
KW - Galaxies: Clusters: General/ Surveys
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AJ....129.1237C&db_key=AST&high=42a068d47507410
N2 - We have analyzed CCD images of 14 Abell clusters in the R filter of the
Southern Abell Clusters Redshifts Survey (SARS) with cz<40,000 km
s-1. We have obtained the luminosity profiles for 507
galaxies, of which 232 (46%) have known redshifts. In order to fit the
luminosity profiles, we used the de Vaucouleurs law for bulge systems
and an exponential profile for disk systems, and we also fitted the
Sérsic's law (rn) to all galaxy profiles. We have
found that 162 galaxies (32%) in the sample have pure r1/4
profiles, 168 (33%) have pure exponential profiles, and 93 (18%) have
luminosity profiles that are well fitted by a combination of bulge and
disk profiles. On the other hand, we could not fit the classical
bulge+disk profile to the remaining 84 galaxies (17%) of the sample. For
such cases we have used only the Sérsic law. We have also
analyzed how seeing and sky cleaning affect the structural and
photometric parameters obtained through profile fitting. In addition, we
have studied several relations between these parameters. We have found
that bulges and disks show consistency with a unique relation in the
mue-logre plane. We also found that bulges and
disks obey a magnitude-size relation in the sense that large bulges and
disks (large re values) have high luminosities. On the other
hand, Sérsic-law fitting parameters n, rs, and
mus show a strong correlation, in agreement with the
findings of other authors, suggesting that not only elliptical galaxies
but all galaxies are likely to be understood as a one-parameter family.
ER -
TY - Journal
T1 - Chandra Spatially Resolved Spectroscopic Study and Multiwavelength Imaging of the Supernova Remnant 3C 397 (G41.1-0.3)
A1 - Safi-Harb, S.
A1 - Dubner, G.
A1 - Petre, R.
A1 - Holt, S. S.
A1 - Durouchoux, P.
JO - Astrophysical Journal
VL - 618
Y1 - 2005/1/1
SP - 321
EP - 338
KW - ISM: Individual: Alphanumeric: G41.1-0.3/ ISM: Individual: Alphanumeric: 3C 397/ Stars: Neutron/ ISM: Supernova Remnants/ X-Rays: ISM
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...618..321S&db_key=AST&high=42a068d47507410
N2 - We present a Chandra observation of the supernova remnant (SNR) 3C 397
(G41.1-0.3) obtained with the Advanced CCD Imaging Spectrometer
(ACIS-S). Previous studies of this SNR have shown that the remnant
harbors a central X-ray ``hot spot'' suggestive of a compact object
associated with 3C 397. With the Chandra data, we can rule out the
nature of the hot spot as a pulsar or a pulsar wind nebula and put an
upper limit on the flux of a hidden compact object of
FX(0.5-10keV)~6×10-13 ergs cm-2
s-1. We found two point sources in the observed Chandra
field. We argue that neither of them is associated with 3C 397 and that
the hard source, CXO J190741.2+070650, which is characterized by a
heavily absorbed spectrum with a strong Fe line, is a newly discovered
active galactic nucleus. The Chandra image reveals arcsecond-scale
clumps and knots that are strongly correlated with the radio VLA image,
except for the X-ray hot spot. Our Chandra spatially resolved
spectroscopic study shows that one-component models are inadequate and
that at least two nonequilibrium ionization thermal components are
needed to fit the spectra of each selected region. The derived average
spectral parameters are consistent with the previous global ASCA fits
performed by Safi-Harb and coworkers. However, the hard component
requires a high abundance of Fe indicating the presence of hot Fe
ejecta. When comparing the eastern with the western lobe, we find that
the column density, the brightness, and the ionization timescales are
generally higher for the western side. This result, combined with our
study of the 3C 397 environs at millimeter wavelengths, indicates a
denser medium to the west of the SNR. Our multiwavelength imaging and
spectral study favors the scenario in which 3C 397 is a ~5300 year old
SNR expanding in a medium with a marked density gradient and is likely
to be encountering a molecular cloud on the western side. We propose
that 3C 397 will evolve into a mixed-morphology SNR.
ER -
TY - Journal
T1 - Model-independent large-scale magnetohydrodynamic quantities in magnetic clouds
A1 - Dasso, S.
A1 - Gulisano, A. M.
A1 - Mandrini, C. H.
A1 - Démoulin, P.
JO - Advances in Space Research
VL - 35
Y1 - 2005/1/1
SP - 2172
EP - 2177
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AdSpR..35.2172D&db_key=AST&high=42a068d47507410
N2 - Magnetic clouds are the interplanetary manifestation of coronal mass
ejections, which are transient expulsions of major quantities of
magnetized plasma, from the Sun toward the heliosphere. The magnetic
flux and helicity are two key physical magnitudes to track solar
structures from the photosphere-corona to the interplanetary medium. To
determine the content of flux and helicity in magnetic clouds, we have
to know their 3D structure. However, since spacecrafts register data
along a unique direction, several aspects of their global configuration
cannot be observed. We present a method to estimate the magnetic flux
and the magnetic helicity per unit length in magnetic clouds, directly
from in situ magnetic observations, assuming only a cylindrical symmetry
for the magnetic field configuration in the observed cross-section of
the cloud. We select a set of 20 magnetic clouds observed by the
spacecraft Wind and estimate their magnetic flux and their helicity per
unit length. We compare the results obtained from our direct method with
those obtained under the assumption of a helical linear force-free
field. This direct method improves previous estimations of helicity in
clouds.
ER -
TY - Journal
T1 - A multi-wavelength study of the western lobe of W50 powered by the galactic microquasar SS 433
A1 - Moldowan, A.
A1 - Safi-Harb, S.
A1 - Fuchs, Y.
A1 - Dubner, G.
JO - Advances in Space Research
VL - 35
Y1 - 2005/1/1
SP - 1062
EP - 1065
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AdSpR..35.1062M&db_key=AST&high=42a068d47507410
N2 - W50 remains the only supernova remnant (SNR) confirmed to harbor a
microquasar: the powerful enigmatic source SS 433. Our past study of
this fascinating SNR revealed two X-ray lobes distorting the radio shell
as well as non-thermal X-rays at the site of interaction between the SS
433 eastern jet and the eastern lobe of W50. In this paper we present
the results of a 75 ks Chandra ACIS-I observation of the peak of
W50-west targeted to: (1) determine the nature of the X-ray emission and
(2) correlate the X-ray emission with that in the radio and infrared
domains. We have confirmed that at the site of interaction between the
western jet of SS 433 and dense interstellar gas the X-ray emission is
non-thermal in nature. The helical pattern observed in radio is also
seen with Chandra. No correlation was found between the infrared and
X-ray emission.
ER -
TY - Journal
T1 - Large scale MHD properties of interplanetary magnetic clouds
A1 - Dasso, S.
A1 - Mandrini, C. H.
A1 - Démoulin, P.
A1 - Luoni, M. L.
A1 - Gulisano, A. M.
JO - Advances in Space Research
VL - 35
Y1 - 2005/1/1
SP - 711
EP - 724
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AdSpR..35..711D&db_key=AST&high=42a068d47507410
N2 - Magnetic Clouds (MCs) are the interplanetary manifestation of Coronal
Mass Ejections. These huge astrophysical objects travel from the Sun
toward the external heliosphere and can reach the Earth environment.
Depending on their magnetic field orientation, they can trigger intense
geomagnetic storms. The details of the magnetic configuration of clouds
and the typical values of their magnetohydrodynamic magnitudes are not
yet well known. One of the most important magnetohydrodynamic quantities
in MCs is the magnetic helicity. The helicity quantifies several aspects
of a given magnetic structure, such as the twist, kink, number of knots
between magnetic field lines, linking between magnetic flux tubes, etc.
The helicity is approximately conserved in the solar atmosphere and the
heliosphere, and it is very useful to link solar phenomena with their
interplanetary counterpart. Since a magnetic cloud carries an important
amount of helicity when it is ejected from the solar corona, estimations
of the helicity content in clouds can help us to understand its
evolution and its coronal origin. In situ observations of magnetic
clouds at one astronomical unit are in agreement with a local helical
magnetic structure. However, since spacecrafts only register data along
a unique direction, several aspects of the global configuration of
clouds cannot be observed. In this paper, we review the general
properties of magnetic clouds and different models for their magnetic
structure at one astronomical unit. We describe the corresponding
techniques to analyze in situ measurements. We also quantify their
magnetic helicity and compare it with the release of helicity in their
solar source for some of the analyzed cases.
ER -
TY - Journal
T1 - XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source observations of SNR RX J1713.7-3946
A1 - Cassam-Chenaï, G.
A1 - Decourchelle, A.
A1 - Ballet, J.
A1 - Sauvageot, J.-L.
A1 - Dubner, G.
A1 - Giacani, E.
JO - Astronomy and Astrophysics
VL - 427
Y1 - 2004/11/1
SP - 199
EP - 216
KW - acceleration of particles/ radiation mechanisms: non-thermal/ ISM: supernova remnants/ ISM: individual objects: G347.3-0.5 (RX J1713.7-3946)/ X-rays: ISM/ stars: individual: 1WGA J1713.4-3949
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...427..199C&db_key=AST&high=42a068d47507410
N2 - We present new results from the observations of the supernova remnant
(SNR) RX J1713.7-3946 (also
G347.3-0.5) performed in five distinct pointings with
the EPIC instrument on board the satellite XMM-Newton. RX J1713.7-3946
is a shell-type SNR dominated by synchrotron radiation in the X-rays.
Its emission (emission measure and photon index) as well as the
absorption along the line-of-sight has been characterized over the
entire SNR. The X-ray mapping of the absorbing column density has
revealed strong well-constrained variations (0.4 × 1022
cm-2 ≤ NH ≤ 1.1 × 1022
cm-2) and, particularly, a strong absorption in the
southwest. Moreover, there are several clues indicating that the shock
front of RX J1713.7-3946 is impacting the clouds responsible for the
absorption as revealed for instance by the positive correlation between
X-ray absorption and X-ray brightness along the western rims. The CO and
HI observations show that the inferred cumulative absorbing column
densities are in excellent agreement with the X-ray findings in
different parts of the remnant on condition that the SNR lies at a
distance of 1.3 ± 0.4 kpc, probably in the Sagittarius galactic
arm, instead of the commonly-accepted value of 6 kpc. An excess in the
CO emission is found in the southwest suggesting that the absorption is
due to molecular clouds. A search for OH masers in the southwestern
region has been unsuccessful, possibly due to the low density of the
clouds. The X-ray mapping of the photon index has also revealed strong
variations (1.8 ≤ Gamma ≤ 2.6). The spectrum is steep in the
faint central regions and flat at the presumed shock locations,
particularly in the southeast. Nevertheless, the regions where the shock
impacts molecular clouds have a steeper spectrum than those where the
shock propagates into a low density medium. The search for the thermal
emission in RX J1713.7-3946 has been unsuccessful leading to a number
density upper limit of 2 × 10-2 cm-3 in the
ambient medium. This low density corresponds to a reasonable kinetic
energy of the explosion provided that the remnant is less than a few
thousand years old. A scenario based on a modified ambient medium due to
the effect of a progenitor stellar wind is proposed and leads to an
estimate of RX J1713.7-3946's progenitor mass between 12 and 16
M⊙. The X-ray bright central point source 1WGA
J1713.4-3949 detected at the center of SNR RX J1713.7-3946 shows
spectral properties very similar to those of the Compact Central Objects
found in SNRs and consistent in terms of absorption with that of the
central diffuse X-ray emission arising from the SNR. It is highly
probable that the point source 1WGA J1713.4-3949 is the compact relic of
RX J1713.7-3946's supernova progenitor.
ER -
TY - Journal
T1 - Spectral Distribution of the Cross Helicity in the Solar Wind
A1 - Milano, L. J.
A1 - Dasso, S.
A1 - Matthaeus, W. H.
A1 - Smith, C. W.
JO - Physical Review Letters
VL - 93
Y1 - 2004/10/1
SP - 155005
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004PhRvL..93o5005M&db_key=AST&high=42a068d47507410
N2 - There are a variety of theoretical and observational indications that
fluctuation energy in astrophysical and space plasma turbulence is
distributed anisotropically in space relative to the magnetic field
direction. The cross helicity, represented by correlations between
velocity and magnetic field fluctuations, enters a magnetohydrodynamic
description on equal footing with the energy, but its anisotropy has not
been examined in the same degree of detail. Here we employ Advanced
Coronal Explorer data to examine the rotational symmetry of the cross
helicity. We find that the normalized cross helicity is associated more
or less equally with all angular components of the fluctuations. This
favors turbulence models that allow for cross communication between
parallel and perpendicular wave numbers, suggesting that
``wavelike'' and ``turbulencelike'' fluctuations are
strongly coupled.
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=42a068d47507410
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 - Geometry of the non-thermal emission in SN 1006. Azimuthal variations of cosmic-ray acceleration
A1 - Rothenflug, R.
A1 - Ballet, J.
A1 - Dubner, G.
A1 - Giacani, E.
A1 - Decourchelle, A.
A1 - Ferrando, P.
JO - Astronomy and Astrophysics
VL - 425
Y1 - 2004/10/1
SP - 121
EP - 131
KW - acceleration of particles/ magnetic fields/ ISM: cosmic rays/ ISM: supernova remnants/ X-rays: individuals: SN 1006
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...425..121R&db_key=AST&high=42a068d47507410
N2 - SN 1006 is the prototype of shell supernova remnants,
in which non-thermal synchrotron emission dominates the X-ray spectrum.
The non-thermal emission is due to the cosmic-ray electrons accelerated
behind the blast wave. The X-ray synchrotron emission is due to the
highest energy electrons, and is thus a tracer of the maximum energy
electrons may reach behind a shock. We have put together all XMM-Newton
observations to build a full map of SN 1006. The very low brightness
above 2 keV in the interior indicates that the bright non-thermal limbs
are polar caps rather than an equator. This implies that the ambient
magnetic field runs southwest to northeast, along the Galactic plane. We
used a combined VLA/Parkes radio map to anchor the spectrum at low
energy, and model the spectra with synchrotron emission from a cut-off
power-law electron distribution, plus a thermal component. We present
radial and azimuthal profiles of the cut-off frequency. The cut-off
frequency decreases steeply with radius towards the center and with
position angle away from the maximum emission. The maximum energy
reached by accelerated particles, as well as their number, must be
higher at the bright limbs than elsewhere. This implies interesting
constraints for acceleration at perpendicular shocks. Overall the
XMM-Newton data is consistent with the model in which the magnetic field
is amplified where acceleration is efficient.
Based on observations obtained with XMM-Newton, an ESA science mission
with instruments and contributions directly funded by ESA member states
and the USA (NASA).
ER -
TY - Journal
T1 - New High-Resolution Radio Observations of the Supernova Remnant CTB 80
A1 - Castelletti, G.
A1 - Dubner, G.
A1 - Golap, K.
A1 - Goss, W. M.
A1 - Velázquez, P. F.
A1 - Holdaway, M.
A1 - Rao, A. Pramesh
JO - Astronomical Journal
VL - 126
Y1 - 2003/11/1
SP - 2114
EP - 2124
KW - ISM: Individual: Alphanumeric: CTB 80/ Stars: Pulsars: Individual: Alphanumeric: PSR B1951+32/ Radio Continuum/ Stars: Neutron/ ISM: Supernova Remnants
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....126.2114C&db_key=AST&high=42a068d47507410
N2 - We report new high-resolution and high-sensitivity radio observations of
the extended supernova remnant (SNR) CTB 80 (G69.0+2.7) at 240, 324,
618, and 1380 MHz. The imaging of CTB 80 at 240 and 618 MHz was
performed using the Giant Metrewave Radio Telescope in India. The
observations at 324 and 1380 MHz were obtained using the Very Large
Array of the National Radio Astronomy Observatory in its C and D
configurations. The new radio images reveal faint extensions for the
asymmetric arms of CTB 80. The arms are irregular, with filaments and
clumps of size 1' (or 0.6 pc at a distance of 2 kpc). The radio image at
1380 MHz is compared with IR and optical emission. The IR-radio
correspondence is excellent along the north arm of CTB 80. Ionized gas
observed in the [S II] line perfectly matches the west and north edges
of CTB 80. The central nebula associated with the pulsar PSR B1951+32
was investigated with an angular resolution of 10"×6". The new
radio image obtained at 618 MHz shows with superb detail structures in
the 8'×4' east-west ``plateau'' nebula that hosts the pulsar on
its western extreme. A twisted filament, about 6' in extent (~3.5 pc),
trails behind the pulsar in an approximate west-east direction. In the
bright ``core'' nebula (size~45"), located to the west of the plateau,
the images show a distortion in the morphology toward the west; this
feature corresponds to the direction in which the pulsar escapes from
the SNR with a velocity of ~240 km s-1. Based on the new
observations, the energetics of the SNR and of the pulsar wind nebula
are investigated.
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/ 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=42a068d47507410
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 - 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=42a068d47507410
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 - 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=42a068d47507410
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 - 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=42a068d47509203
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=42a068d47509203
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 - The spectroscopic orbits and other parameters of the symbiotic binary FN Sgr
A1 - Brandi, E.
A1 - Mikolajewska, J.
A1 - Quiroga, C.
A1 - Belczynski, K.
A1 - Ferrer, O. E.
A1 - García, L. G.
A1 - Pereira, C. B.
JO - Astronomy and Astrophysics
VL - 440
Y1 - 2005/9/1
SP - 239
EP - 248
KW - stars: binaries: eclipsing/ stars: binaries: symbiotic/ stars: fundamental parameters/ stars: individual: FN Sgr
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...440..239B&db_key=AST&high=42a068d47511140
N2 - We present a study of the eclipsing symbiotic binary FN Sgr with a
period of 568.3 days determined photometrically and confirmed
spectroscopically. The hot component underwent a 2.5 mag eruption
covered by most of our spectroscopic observations. In particular, we
have determined for the first time spectroscopic orbits based on the
radial velocity curves for both components. A set of blue absorption
lines resembling an A-F type star is present in all our spectra and they
seem to be associated with the hot component. Based on the light curve,
we derive the red giant's radius (140~ R⊙) and the
orbital inclination (i = 80°). We find that FN Sgr is similar to
other S-type symbiotic binaries, composed by an M 5-type giant (M_g=1.5
M⊙) and a hot white dwarf (Mh = 0.7~
M⊙, R_h= 0.2~ R⊙) with a binary
separation of ~1.6 AU. The red giant is just filling its Roche lobe and
a geometrically and optically thick accretion disk is likely to be
present around the low-mass accretor. The evolution of Th and
Lh along the active phase argues in favour of accretion disk
instabilities similar to those of Z And. We have also studied spectral
changes and photometric variations as a function of both the hot
component activity and the orbital motion.
ER -
TY - Journal
T1 - Globular clusters as tracers of stellar bimodality in elliptical galaxies: the case of NGC 1399
A1 - Forte, Juan C.
A1 - Faifer, Favio
A1 - Geisler, Doug
JO - Monthly Notices of the Royal Astronomical Society
VL - 357
Y1 - 2005/2/1
SP - 56
EP - 68
KW - galaxies: clusters: individual: NGC 1399/ galaxies: haloes/ galaxies: star clusters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.357...56F&db_key=AST&high=42a068d47511140
N2 - Globular cluster systems (GCSs) frequently show a bimodal distribution
of cluster integrated colours. This work explores the arguments to
support the idea that the same feature is shared by the diffuse stellar
population of the galaxy they are associated with. The particular case
of NGC 1399, one of the dominant central galaxies in the Fornax cluster,
for which a new B surface brightness profile and (B-RKC)
colours are presented, is discussed taking advantage of a recently
published wide-field study of its GCS. The results show that the galaxy
brightness profile and colour gradient, as well as the behaviour of the
cumulative globular cluster specific frequency, are compatible with the
presence of two dominant stellar populations, associated with the
so-called `blue' and `red' globular cluster families. These globular
families are characterized by different intrinsic specific frequencies
(defined in terms of each stellar population): Sn= 3.3 +/-
0.3 in the case of the red globulars and Sn= 14.3 +/- 2.5 for
the blue ones. We stress that this result does not necessarily conflict
with recent works that point out a clear difference between the
metallicity distribution of (resolved) halo stars and globulars when
comparing their number statistics. The region within 0.5arcmin of the
centre shows a deviation from the model profile (in both surface
brightness and colour) that may be explained in terms of the presence of
a bulge-like high-metallicity component. Otherwise, the model gives an
excellent fit up to 12arcmin (or 66.5Kpc) from the centre, the
galactocentric limit of our blue brightness profile. The inferred
specific frequencies imply that, in terms of their associated stellar
populations, the formation of the blue globulars took place with an
efficiency about six times higher than that corresponding to their red
counterparts. The similarity of the spatial distribution of the blue
globulars with that inferred for dark matter, as well as with that of
the X-ray-emitting hot gas associated with NGC 1399, is emphasized. The
impact of a relatively inconspicuous low-metallicity population, that
shares the properties of the blue globulars, as a possible source of
chemical enrichment early in the formation history of the galaxy is also
briefly discussed.
ER -
TY - Journal
T1 - The Globular Cluster System of NGC 1399. III. VLT Spectroscopy and Database
A1 - Dirsch, B.
A1 - Richtler, T.
A1 - Geisler, D.
A1 - Gebhardt, K.
A1 - Hilker, M.
A1 - Alonso, M. V.
A1 - Forte, J. C.
A1 - Grebel, E. K.
A1 - Infante, L.
A1 - Larsen, S.
A1 - Minniti, D.
A1 - Rejkuba, M.
JO - Astronomical Journal
VL - 127
Y1 - 2004/4/1
SP - 2114
EP - 2132
KW - Cosmology: Dark Matter/ Galaxies: Elliptical and Lenticular/ cD/ Galaxies: Halos/ Galaxies: Individual: NGC Number: NGC 1399/ Galaxies: Kinematics and Dynamics/ Galaxies: Star Clusters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127.2114D&db_key=AST&high=42a068d47511140
N2 - Radial velocities of 468 globular clusters around NGC 1399, the central
galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask
Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest
sample of globular cluster velocities around any galaxy obtained so far.
The mean velocity uncertainty is 50 km s-1. This data sample
is accurate and large enough to be used in studies of the mass
distribution of NGC 1399 and the properties of its globular cluster
system. Here we describe the observations and the reduction procedure,
and we discuss the uncertainties of the resulting velocities. The
complete sample of cluster velocities that is used in a dynamical study
of NGC 1399 is tabulated. A subsample is compared with previously
published values.
Based on observations collected at the European Southern Observatory,
Cerro Paranal, Chile; ESO program 66.B-0393.
ER -
TY - Journal
T1 - The Globular Cluster System of NGC 1399. II. Kinematics of a Large Sample of Globular Clusters
A1 - Richtler, T.
A1 - Dirsch, B.
A1 - Gebhardt, K.
A1 - Geisler, D.
A1 - Hilker, M.
A1 - Alonso, M. V.
A1 - Forte, J. C.
A1 - Grebel, E. K.
A1 - Infante, L.
A1 - Larsen, S.
A1 - Minniti, D.
A1 - Rejkuba, M.
JO - Astronomical Journal
VL - 127
Y1 - 2004/4/1
SP - 2094
EP - 2113
KW - Cosmology: Dark Matter/ Galaxies: Elliptical and Lenticular/ cD/ Galaxies: Halos/ Galaxies: Individual: NGC Number: NGC 1399/ Galaxies: Kinematics and Dynamics/ Galaxies: Star Clusters
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127.2094R&db_key=AST&high=42a068d47511140
N2 - We study the kinematics and dynamics of the globular cluster system of
NGC 1399, the brightest elliptical galaxy near the center of the Fornax
cluster of galaxies. The observational data consists of
medium-resolution spectra, obtained at the Very Large Telescope with
FORS2 and the Mask Exchange Unit (MXU). Our sample comprises 468 radial
velocities in the magnitude range 20R<23. This is the
largest sample of globular cluster velocities around any galaxy obtained
so far. Typical velocity uncertainties are 50 km s-1,
significantly improving on earlier samples. The radial range is
2'', corresponding to 11 kpc to 50 kpc
of galactocentric distance. The shape of the velocity distribution of
the sample is compatible with being a Gaussian distribution. However,
under moderate error selection, a slight asymmetry is visible between
high and low radial velocities. We find bright clusters with radial
velocities below 800 km s-1, while they are not found at the
corresponding high-velocity side above 2000 km s-1. There is
the possibility that unbound clusters and/or objects in the foreground
contaminate the NGC 1399 cluster sample. Under strong error selection,
practically no objects are found with velocities lower than 800 km
s-1 or higher than 2000 km s-1. Since the extreme
velocities influence the velocity dispersion considerably, uncertainty
regarding the exact value of the dispersion remains. With the above
velocity limits, we derive a projected velocity dispersion for the total
sample of 274+/-9 km s-1 which within the uncertainties
remains constant over the entire radial range. Without any velocity
restriction, it increases to 325 km s-1. Guided by the
bimodal color distribution of clusters, we distinguish between red
clusters (C-R>1.6) and blue clusters (C-R<1.6), and find velocity
dispersions for these groups of 255+/-13 and 291+/-14 km s-1,
respectively, again radially constant. Any possible rotation of either
of these cluster populations is below the detection limit, with the
exception of a weak signature of rotation for the blue clusters more
distant than 6'. Spherical models point to a circular velocity of
419+/-30 km s-1, assuming isotropy for the red clusters. This
value is constant out to 40 kpc. The inferred dark halo potential can be
well represented by a logarithmic potential. A halo of the NFW type also
provides a good fit to the observations. The orbital structure of the
clusters can only be weakly constrained. It is consistent with isotropy
for the red clusters and a slight tangential bias for the blue clusters.
Some mass profiles derived from X-ray analyses do not agree with a
constant circular velocity within our radial range, irrespective of its
exact value. Interpreting the extreme low radial velocities as space
velocities of bound clusters near their pericentric distances would
require an extension of the cluster system of at least 200 kpc.
Implications for formation scenarios of the cluster system are briefly
commented on.
Based on observations collected at the European Southern Observatory,
Cerro Paranal, Chile; ESO program 66.B-0393.
ER -