The subgiant CH stars

A new class of peculiar stars has been discovered on objective-prism plates. These objects have G-type spectra with weak metallic lines but enhanced features of CH and the s-process elements, and most of these stars have high space velocities. Photometrically they show the high violet opacity seen in other carbon-rich stars of similar temperature. Several lines of evidence indicate visual absolute magnitudes near M9 = +2. These stars are similar in composition to, and much more common per unit volume of space than, the betterknown CII stars. It is proposed that these objects acquire their unusual surface compositions in events that partially mix Population II red giants, and that later, as they evolve back up the red-giant branch, they become CH stars. These "subgiant CII stars" are probably present in several globular clusters. Subject headings: carbon stars - high-velocity stars - Population II stars - spectral classification - stellar evolution