The Binary Nature of the Subgiant CH Stars

Abstract

Repeated radial velocities have been measured for a sample of 10 subgiant CH (sgCH) stars over a period of about 15 years. Long-term velocity variations are exhibited by all but one star, and spectroscopic orbits have been calculated for six of them. The periods are long, ranging from 876 to 4144 days. The distribution of eccentricities and mass functions for sgCH star orbits are similar to those for giant barium and CH stars, exhibiting significant orbital dissipation relative to normal late-type binaries. It is concluded that all sgCH stars are binaries, and like the barium and CH stars, they have had mass transferred from a former asymptotic giant-branch star.

10 Latex pages, including 2 figures. Accepted by PASP. Also available at http://www.hia.nrc.ca/eprints.html

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