Asymptotic giant and red giant branch stars in globular clusters.
Abstract
Stars of unusual composition were found in the course of a spectroscopic survey of the red-giant (RG) and asymptotic-giant branch (AGB) stars of the metal-weak globular clusters M92 and M22. These stars have unusually strong CN and CH band strengths and apparently strong metal (Fe, Ca, Mn) lines as well. They may be mixed stars in which the atmospheric hydrogen is depleted and the C, N and 0 abundances enhanced. The typical RG and AGB stars exhibit no apparent spectroscopic differences. A moderate resolution spectrophotometric survey also revealed no difference in the spectral energy distributions except for wavelengths below the Balmer jump. These observations can be explained by a surface gravity difference resulting from the observed luminosity difference between the AGB and RG and a mass loss not exceeding 0.2 dex. Key words: globular clusters - post-horizontal-branch evolution
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 1971
- Bibcode:
- 1971A&A....14..111S