Issue |
A&A
Volume 507, Number 1, November III 2009
|
|
---|---|---|
Page(s) | L1 - L4 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/200913205 | |
Published online | 27 October 2009 |
Letter to the Editor
Massive binaries as the source of abundance anomalies in globular clusters
1
Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands e-mail: [S.E.deMink;O.R.Pols]@uu.nl
2
Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: nlanger@astro.uni-bonn.de
3
Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Brussels, Belgium e-mail: Robert.Izzard@ulb.ac.be
Received:
29
August
2009
Accepted:
1
October
2009
Abundance anomalies observed in globular cluster stars
indicate pollution with material processed by hydrogen
burning. Two main sources have been suggested: asymptotic giant
branch (AGB) stars and massive stars rotating near the break-up
limit (spin stars).
We propose massive binaries as an alternative source of processed material.
We compute the evolution of a 20 star in a close binary
considering the effects of non conservative mass and
angular momentum transfer and of rotation and tidal interaction to
demonstrate the principle. We find that this system sheds about
10
of material, nearly the entire envelope of the primary
star. The ejecta are enriched in He, N, Na, and Al and depleted
in C and O, similar to the abundance patterns observed in gobular
cluster stars. However, Mg is not significantly depleted in the ejecta of this model.
In contrast to the fast, radiatively driven winds
of massive stars, this material is typically ejected with low
velocity. We expect that it remains inside the potential well of
a globular cluster and becomes available for the formation or
pollution of a second generation of stars.
We estimate that the amount of processed low-velocity material
ejected by massive binaries is greater than the contribution of AGB
stars and spin stars combined, assuming that the majority of
massive stars in a proto-globular cluster interact with a
companion and return their envelope to the interstellar medium.
If we take the possible contribution of intermediate mass stars in binaries into account and assume that the ejecta are diluted
with an equal amount of unprocessed
material, we find that this scenario can potentially provide enough
material to form a second generation of low-mass stars, which is
as numerous as the first generation of low-mass stars,
without the need to make commonly adopted assumptions, such as
preferential loss of the first generation of stars, external
pollution of the cluster, or an anomalous initial mass function.
Key words: stars: abundances / stars: binaries: close / Galaxy: globular clusters: general / ISM: general
© ESO, 2009
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