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Session 64 - Globular Clusters.
Oral session, Tuesday, January 14
Piers 2/3,
Only two types of carbon stars are known to have abundances and kinematics which are indicative of membership in the Galactic halo: giant CH stars, and their progenitors, dwarf carbon stars (dCs). In both cases, their enhanced abundances of carbon and s-process elements are thought to be the result of mass transfer from evolved, carbon-rich companions which have now faded to become white dwarfs. Radial velocity surveys of field dC and CH stars have demonstrated that these binaries are sufficiently compact that, if present in globular clusters, they are expected to be dynamically hard (i.e., capable of avoiding disruption over a Hubble time). As such, they would represent a new tool for studying the abundance of cluster binaries containing degenerate (white-dwarf) secondaries. We describe the first-ever search for globular cluster dC stars, using CFHT and Keck II observations of the nearby, low-concentration cluster M71. We also discuss the properties of the three known giant CH stars in globular clusters, and interpret the results in terms of models for dynamical evolution of hard binaries in dense environments.
