The Binary Frequency Among Carbon‐enhanced,s‐Process–rich, Metal‐poor Stars

We discuss radial velocities for a sample of carbon-enhanced, s-process rich,very metal-poor stars (CEMP-s hereafter), analyzed with high-resolutionspectroscopy obtained over multiple epochs. We find that ~68% of the stars inthe sample show evidence of radial velocity variations. The expected detectionfraction for these stars, adopting the measured binary fraction in the field(~60%), and assuming that they share the same period and eccentricitydistribution, is ~22%. Even if one assumes that the true binary fraction ofthese stars is 100%, the expected detection percentage is ~36%. These valuesindicate that the binary fraction among CEMP-s stars is higher than the fieldbinary fraction, suggesting that all of these objects are in double (ormultiple) systems. The fact that the observed frequency of velocity variationexceeds the expected detection fraction in the case of an assumed binaryfraction of 100% is likely due to a more restricted distribution of orbitalperiods for these objects, as compared to normal field binaries. Our resultsindicate that CEMP-s stars are the metal-poor analogues of classical CH-stars.Comment: 22 pages, Accepted for publication on Ap