Bimodal cyanogen distributions in moderately metal-poor globular clusters. I - Carbon and nitrogen abundances for six M5 giants

• Published in: Publications of the Astronomical Society of the Pacific Vol. 97; pp. 373 - 381
• Main Authors: Langer, G. E., Kraft, R. P., Friel, E. D.
• Format: Journal Article
• Language: English
• Published: 01.05.1985
• ISSN: 0004-6280; 1538-3873
• DOI: 10.1086/131547

In order to determine carbon and nitrogen abundances for three CN-strong and three CN-weak red giants in the globular cluster M5, spectrum-synthesis techniques are used. It is shown that all six stars have approximately the same luminosity and surface temperature and are, presumably, in the same stage of evolution. CN-strong and CN-weak stars that sit side by side on the C-M diagram are found to have significantly different carbon and nitrogen abundances, but there is no evidence for a difference in the total (C+N) abundance. The CN band strengths indicate that the carbon abundances should be shifted to higher values by about 0.2 dex while the nitrogen abundances should be shifted by about 0.2 dex to lower values. The observed abundances are interpreted by a simple mixing scenario in which C-N processing proceeds at different rates in apparently similar stars.