Issue |
A&A
Volume 417, Number 1, April I 2004
|
|
---|---|---|
Page(s) | 217 - 234 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20034325 | |
Published online | 16 March 2004 |
Understanding B-type supergiants in the low metallicity environment of the SMC
1
The Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700, Santa Cruz de La Palma, Canary Islands, Spain
2
The Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland
3
Universitäts-Sternwarte München, Scheinstr. 1, 81679, Germany
Corresponding author: C. Trundle, ct@ing.iac.es
Received:
16
September
2003
Accepted:
5
December
2003
Spectroscopic analyses of 7 SMC B-type supergiants and 1 giant have been
undertaken using high resolution optical data obtained on the vlt with
uves. fastwind, a non-LTE, spherical, line-blanketed model atmosphere
code was used to derive atmospheric and wind parameters of these stars as well
as their absolute abundances. Mass-loss rates, derived from Hα
profiles, are in poor agreement with metallicity dependent theoretical
predictions. Indeed the wind-momenta of the SMC stars appear to be in good
agreement with the wind-momentum luminosity relationship (WLR) of Galactic
B-type stars, a puzzling result given that line-driven wind theory predicts a
metallicity dependence. However the galactic stars were analysed using
unblanketed model atmospheres which may mask any dependence on metallicity. A mean
nitrogen enhancement of a factor of 14 is observed in the supergiants whilst
only an enrichment of a factor of 4 is present in the giant, AV216. Similar
excesses in nitrogen are observed in O-type dwarfs and supergiants in the same
mass range, suggesting that the additional nitrogen is produced while the stars
are still on the main-sequence. These nitrogen enrichments can be reproduced by
current stellar evolution models, which include rotationally induced mixing,
only if large initial rotational velocities of 300 km s-1 are invoked. Such
large rotational velocities appear to be inconsistent with observed
distributions for O-type stars and B-type supergiants. Hence it is suggested
that the currently available stellar evolution models require more efficient
mixing for lower rotational velocities.
Key words: stars: atmospheres / stars: early-type / stars: supergiants / stars: mass-loss / stars: abundances / stars: evolution
© ESO, 2004
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