Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-12-16
Astrophys.J. 625 (2005) 825-832
Astronomy and Astrophysics
Astrophysics
22 pages, Accepted for publication on ApJ
Scientific paper
10.1086/428104
We discuss radial velocities for a sample of carbon-enhanced, s-process rich, very metal-poor stars (CEMP-s hereafter), analyzed with high-resolution spectroscopy obtained over multiple epochs. We find that ~68% of the stars in the sample show evidence of radial velocity variations. The expected detection fraction for these stars, adopting the measured binary fraction in the field (~60%), and assuming that they share the same period and eccentricity distribution, is ~22%. Even if one assumes that the true binary fraction of these stars is 100%, the expected detection percentage is ~36%. These values indicate that the binary fraction among CEMP-s stars is higher than the field binary fraction, suggesting that all of these objects are in double (or multiple) systems. The fact that the observed frequency of velocity variation exceeds the expected detection fraction in the case of an assumed binary fraction of 100% is likely due to a more restricted distribution of orbital periods for these objects, as compared to normal field binaries. Our results indicate that CEMP-s stars are the metal-poor analogues of classical CH-stars.
Beers Timothy C.
Carretta Eugenio
Gratton Raffaele G.
Lucatello Sara
Ryan Sean G.
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