Issue |
A&A
Volume 404, Number 3, June IV 2003
|
|
---|---|---|
Page(s) | 975 - 990 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20030512 | |
Published online | 06 June 2003 |
Stellar evolution with rotation
X. Wolf-Rayet star populations at solar metallicity
Geneva Observatory, 1290 Sauverny, Switzerland e-mail: Andre.Maeder@obs.unige.ch
Corresponding author: G. Meynet, Georges.Meynet@obs.unige.ch
Received:
5
February
2003
Accepted:
6
March
2003
We examine the properties of Wolf-Rayet (WR) stars predicted by models
of rotating stars taking account of the new mass loss rates for O-type stars
and WR stars (Vink et al. 2000, 2001; Nugis & Lamers 2000)
and of the wind anisotropies induced by rotation. We find that the rotation velocities v
of WR stars are modest, i.e. about 50 km s-1, not very dependent on the initial v
and masses. For the most massive stars, the evolution of v is very strongly influenced
by the values of the mass loss rates; below ~12 the evolution of rotation
during the MS phase and later phases is dominated by the internal coupling. Massive stars
with extreme rotation may skip the LBV phase.
Models having a typical v for the O-type stars have WR lifetimes on the average two times longer
than for non-rotating models. The increase of the WR lifetimes is mainly due to that of
the H-rich eWNL phase. Rotation allows a transition WN/WC phase to be present for
initial masses lower than 60
. The durations of the other WR subphases are
less affected by rotation. The mass threshold for forming WR stars is lowered from
37 to 22
for typical rotation. The comparisons of the predicted number ratios
WR/O, WN/WC and of the number of transition WN/WC stars show very good agreement with models with
rotation, while this is not the case for models with the present-day mass loss rates
and no rotation.
As to the chemical abundances in WR stars, rotation brings only very small changes
for WN stars, since they have equilibrium CNO values. However, WC stars with rotation
have on average lower C/He and O/He ratios. The luminosity distribution of WC stars
is also influenced by rotation.
Key words: stars: evolution / stars: rotation / stars: Wolf-Rayet
© ESO, 2003
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