Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2010-07-13
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
final version after proofs
Scientific paper
The determination of the Ba abundance in globular cluster (GC) stars is a very powerful test to address several issues in the framework of multiple population scenarios. We measured the Ba content for a sample of more than 1200 stars in 15 Galactic GCs, using high-resolution FLAMES/Giraffe spectra. We found no variation in [Ba/Fe] ratios for different stellar populations within each cluster; this means that low-mass asymptotic giant branch stars do not significantly contribute to the intra-cluster pollution. Very interestingly, we obtained that the fraction of Ba-stars in first generation (FG) stars is close to the values derived for field stars ($\sim$2\%); on the other hand, second generation (SG) stars present a significant lower fraction. An independent and successful test, based on radial velocity variations among giant stars in NGC~6121, confirms our finding: the binary fraction among FG stars is about $\sim$12\% to be compared with $\sim$1\% of SG stars. This is an evidence that SG stars formed in a denser environment, where infant mortality of binary systems was particularly efficient.
Bragaglia Angela
Carretta Eugenio
D'Orazi Valentina
Gratton Raffaele
Lucatello Sara
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