The Role of Binaries in the Carbon Star Phenomenon

This presentation reviews the role that binaries play in the production of Barium, CH, and S stars. New radial velocity observations connrming the binary nature of subgiant CH stars are also discussed. Perhaps the most important part of the presentation is evidence that the early R-type carbon stars exhibit no binaries. It is suggested that they were once all binaries, but having small separations, a coalescing companion has caused them to mix near the helium core ash.