The Anomalous Giant Branch of ω Centauri

Abstract

The giant branch of ω Cen is much narrower in the I, (V-I) diagram than in the V, (B-V) diagram but at least 24 stars which lie on the red side of the giant branch are radial velocity members (Lloyd Evans 1977), (Lloyd Evans, to be published). Spectra of these stars show, with only one exception, stronger metal lines than stars of similar (V-I) color on the main giant branch (comparable to stars in 47 Tuc), strong CN bands where the stellar temperature allows and strong Ba II 4554 Å. The Ba II star RGO 371 (Dickens and Bell 1976) is a typical member of the group. The Cepheid V29 also shows strong CN bands and strong Ba II. A start has been made on a spectroscopic search for stars on the main giant branch showing these anomalies and the sample of stars with VI photometry is being enlarged. An explanation of the properties of these stars would appear to require both a large primordial metal content and mixing of processed material to the surface.