Issue |
A&A
Volume 452, Number 1, June II 2006
|
|
---|---|---|
Page(s) | 273 - 284 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20053859 | |
Published online | 17 May 2006 |
Effects of metallicity, star-formation conditions, and evolution in B and Be stars
I. Large Magellanic Cloud, field of NGC 2004
1
GEPI, UMR 8111 du CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France e-mail: christophe.martayan@obspm.fr
2
Royal Observatory of Belgium, 3 avenue circulaire, 1180 Brussels, Belgium
3
Institut d'Astrophysique de Paris (IAP), 98bis boulevard Arago, 75014 Paris, France
4
Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, 3001 Belgium
Received:
19
July
2005
Accepted:
15
January
2006
Aims.To statistically study the effects of the metallicity, star-formation conditions, and evolution on the behaviour of massive stars and, more particularly, of B and Be stars, we observed large samples of stars in the Magellanic Clouds for the first time. In this article we present the first part of this study.
Methods.Spectroscopic observations of hot stars belonging to the young cluster LMC-NGC 2004 and
its surrounding region were carried out with the VLT-GIRAFFE facilities in MEDUSA mode.
We determined the fundamental parameters (Teff, ,
, and radial velocity)
for all B and Be stars in the sample thanks to a code developed in our group. The effect
of fast rotation (stellar flattening and gravitational darkening) are taken into account
in this study. We also determined the age of observed clusters. We then compared the mean
obtained for field and cluster B and Be stars in the Large Magellanic Cloud (LMC)
with the ones in the Milky Way (MW).
Results.We find, in particular, that Be stars rotate
faster in the LMC than in the MW, in the field as well as in clusters. We discuss the
relations between , metallicity, star-formation conditions, and stellar evolution
by comparing the LMC with the MW. We conclude that Be stars began their main sequence
life with an initial rotational velocity higher than the one for B stars. It is
probable that only part of the B stars, those with a sufficient initial rotational velocity,
can become Be stars. This result may explain the differences in the proportion of Be
stars in clusters with similar ages.
Key words: stars: early-type / stars: emission-line, Be / galaxies: Magellanic Clouds / stars: fundamental parameters / stars: evolution / stars: rotation
© ESO, 2006
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