3,340 research outputs found
Constraining the third dredge-up via carbon stars in the Magellanic Clouds
We use the available data for Magellanic Cloud carbon stars to constrain the
efficiency of the third dredge-up process in TP-AGB models. We show that star
counts in LMC clusters provide quite stringent limits to the lifetime of the
C-star phase, with a duration between 2 and 3 Myr for stars in the mass range
from 1.5 to 2.8 Msun. Together with the luminosity functions of field C stars,
this information allows us to re-calibrate the third dredge-up parameters log
T_b_dred and lambda in TP-AGB models that include variable molecular opacities
(Marigo 2002). Preliminary results are presented here.Comment: in proceedings of the St. Luc conference ``CNO in the Universe'',
eds. C. Charbonnel, D. Schaerer, & G. Meynet, ASP Conference Series, in pres
Stellar populations in the Galactic bulge
AIMS:The aim of this paper is to study the characteristics of the stellar
populations and the metallicity distribution in the Galactic bulge. We study
the entire stellar population, but also retrieve information using only the red
clump stars. METHODS: To study the characteristics of the stellar populations
and the metallicity distribution in the Galactic bulge, we compared the output
of the galaxy model TRILEGAL, which implements the Binney et al. (1997) bulge
model, with observations from 2MASS and OGLE-II. A minimisation procedure has
been set up to retrieve the best fitting model with different stellar
populations and metallicity distributions. RESULTS: Using the TRILEGAL code we
find that the best model resembling the characteristics of the Galactic bulge
is a model with the distance to the Galactic centre kpc, the major axis ratios of the bar , and the angle between the
Sun-centre line and the bar . Using these
parameters the best model is found for a burst of 8 Gyr, although it is almost
indistinguishable from models with ages of 9 and 10 Gyr. The metallicity
distribution found is consistent with metallicity distributions in the
literature based on spectroscopic results.Comment: A&A accepte
Clump stars in the Solar Neighbourhood
Hipparcos data has allowed the identification of a large number of clump
stars in the Solar Neighbourhood. We discuss our present knowledge about their
distributions of masses, ages, colours, magnitudes, and metallicities. We point
out that the age distribution of clump stars is ``biased'' towards
intermediate-ages. Therefore, the metallicity information they contain is
different from that provided by the local G dwarfs. Since accurate abundance
determinations are about to become available, these may provide useful
constraints to chemical evolution models of the local disc.Comment: 6 pages, proc. of the Sept. 20-24, 1999 Vulcano Workshop "The
chemical evolution of the Milky Way: stars vs. clusters", eds. F. Matteucci,
F. Giovanell
Evolution of zero-metallicity massive stars
We discuss the evolutionary properties of primordial massive and very massive
stars, supposed to have formed from metal-free gas. Stellar models are
presented over a large range of initial masses (8 Msun <= Mi <= 1000 Msun),
covering the hydrogen- and helium-burning phases up to the onset of carbon
burning. In most cases the evolution is followed at constant mass. To estimate
the possible effect of mass loss via stellar winds, recent analytic formalisms
for the mass-loss rates are applied to the very massive models (Mi >= 120
Msun).Comment: Invited talk at IAU Symp. 212, ``A Massive Star Odyssey, from Main
Sequence to Supernova'', K.A. van der Hucht, A. Herrero, C. Esteban (eds.), 7
pages, 5 postscript figure
The Garching-Bonn Deep Survey (GaBoDS) Wide-Field-Imaging Reduction Pipeline
We introduce our publicly available Wide-Field-Imaging reduction pipeline
THELI. The procedures applied for the efficient pre-reduction and astrometric
calibration are presented. A special emphasis is put on the methods applied to
the photometric calibration. As a test case the reduction of optical data from
the ESO Deep Public Survey including the WFI-GOODS data is described. The
end-products of this project are now available via the ESO archive Advanced
Data Products section.Comment: 6 pages, 3 figures, proceedings of ESO Calibration Workshop 200
Extended star formation history of the star cluster NGC 2154 in the Large Magellanic Cloud
The colour-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud star cluster NGC 2154 and its adjacent field has been analysed using Padova stellar models to determine the clusterÂŽs fundamental parameters and its star formation history. Deep BR CCD photometry, together with synthetic CMDs and integrated luminosity functions, has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyr, which began approximately 2.3 Gyr ago and ended 1.1 Gyr ago. However, the physical reality of such a prolonged period of star formation is questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70 per cent) seems to exist in NGC 2154.Fil: Baume, Gustavo Luis. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: Carraro, Giovanni. UniversitĂ di Padova; ItaliaFil: Costa, E.. Universidad de Chile; ChileFil: Mendez, R. A.. Universidad de Chile; ChileFil: Girardi, L.. Osservatorio Astronomico di Padova; Itali
The nature of the giant diffuse non-thermal source in the A3411-A3412 complex
VLA deep radio images at 1.4 GHz in total intensity and polarization reveal a
diffuse non-thermal source in the interacting clusters A3411 - A3412. Moreover
a small-size low power radio halo at the center of the merging cluster A3411 is
found. We present here new optical and X-ray data and discuss the nature and
properties of the diffuse non-thermal source. We suggest that the giant diffuse
radio source is related to the presence of a large scale filamentary structure
and to multiple mergers in the A3411-A3412 complex.Comment: 7 pages, 6 figures, accepted for publication in MNRA
Uncertainties in stellar evolution models: convective overshoot
In spite of the great effort made in the last decades to improve our
understanding of stellar evolution, significant uncertainties remain due to our
poor knowledge of some complex physical processes that require an empirical
calibration, such as the efficiency of the interior mixing related to
convective overshoot. Here we review the impact of convective overshoot on the
evolution of stars during the main Hydrogen and Helium burning phases.Comment: Proc. of the workshop "Asteroseismology of stellar populations in the
Milky Way" (Sesto, 22-26 July 2013), Astrophysics and Space Science
Proceedings, (eds. A. Miglio, L. Girardi, P. Eggenberger, J. Montalban
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