Issue |
A&A
Volume 373, Number 2, July II 2001
|
|
---|---|---|
Page(s) | 555 - 571 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20010596 | |
Published online | 15 July 2001 |
Stellar evolution with rotation. VII.
Low metallicity models and the blue to red supergiant ratio in the SMC
Geneva Observatory 1290 Sauverny, Switzerland e-mail: Georges.Meynet@obs.unige.ch
Corresponding author: A. Maeder, Andre.Maeder@obs.unige.ch
Received:
15
March
2001
Accepted:
12
April
2001
We calculate a grid of models with and without
the effects of axial rotation for massive stars in the range of 9
to and metallicity
appropriate for the
SMC. Remarkably, the ratios
of the angular velocity to the break-up angular velocity
grow strongly during the evolution of high mass stars,
contrary to the situation at
.
The reason is that at low Z, mass loss is smaller and the removal
of angular momentum during evolution much weaker, also there is an
efficient outward transport of angular momentum
by meridional circulation. Thus, a much larger
fraction of the stars at lower Z reach
break-up velocities and rotation may thus be
a dominant effect at low
Z. The models with rotation well
account for the long standing problem of the large numbers
of red supergiants observed in low Z galaxies, while current
models with mass loss were predicting no red supergiants.
We discuss in detail the physical effects of rotation which
favour a redwards evolution in the HR diagram. The models also predict
large N enrichments during the evolution of
high mass stars. The predicted relative N-enrichments
are larger at Z lower than solar and this is
in very good agreement with the observations for A-type supergiants
in the SMC.
Key words: stars: evolution / stars: rotation / supergiant / magellanic clouds
© ESO, 2001
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.