Subgiant CH stars. II - Chemical compositions and the evolutionary connection with barium stars

Chemical abundances in 15 subgiant CH stars, five barium stars, and four objects classified as metal-deficient barium stars are determined through model-atmosphere analyses of high-resolution photographic echelle spectrograms. The stars in each of these groups show enhanced surface abundances of carbon and the very heavy elements produced by s-process neutron-capture reactions. The atmospheric parameters of subgiant CH stars are found to be typical of F- and G-type main-sequence stars and subgiants. Barium stars are more luminous G- and K-type giants. Both classes of objects constitute about 1 percent of their respective populations, and exhibit a high incidence (about 100 percent) of the membership in wide spectroscopic binaries. Subgiant CH stars occur on the main sequence, but only in the T(eff) range 6000-6800 K. It is argued that subgiant CH stars are created when an AGB star in a wide binary contaminates its main-sequence companion with carbon and s-processed material.