The unusual red giants in M5, M10 and M92.
Abstract
Summary. The stars that were reported to be unusual red giants in the globular clusters M 5, M 10, and M 92 have been observed spectroscopically at a dispersion of 130 A/mm. The unusual star in M 5 (IV-59) and the one in M 10 (1018) have radial velocities that are consistent with cluster membership. New radial velocity data together with the available proper motion and photometric data indicate that the M 92 stars are not cluster members, but are field stars with normal compositions. The spectrograms of IV-59 and 1018 confirm Osborn's earlier result that these stars have enhanced 24216 CN bands. The unusual strengths of their CN bands are not the result of low surface gravity, but are the result of unusual composition. There is evidence that the CN enhancement in IV-59 is at least partially caused by an over-abundance of carbon. It is suggested that the unusual compositions of IV-59 and 1018 were produced by the same mixing process that produced the carbon- rich atmospheres of the CH stars. Key words: globular clusters - red giants - unusual compositions - CH stars
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 1973
- Bibcode:
- 1973A&A....25..409Z