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The Role of Mixing and Primordial Abundance Variations in 47 Tucanae and ω Centauri

Published online by Cambridge University Press:  14 August 2015

John Norris
John Norris*
Affiliation:
Mount Stromlo and Siding Spring Observatory, Australian National University

Extract

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It has become clear in recent years that widespread and complex abundance variations exist among the stars of several globular clusters. ω Cen is the prime example, containing CH stars, weak-G-band stars, CN strong stars, TiO stars, and (not least) RR Lyrae stars possessing an anomalous range in calcium line strengths. (Harding 1962; Freeman and Rodgers 1975; Norris and Bessell 1975, 1977; Dickens and Bell 1976; Bessell and Norris 1976; Lloyd Evans 1977) The extent to which these phenomena result from primordial abundance variations or from the mixing to the surface of material processed by nuclear reactions is currently the subject of some debate. The present paper presents a short account of investigations of the giant and horizontal branches of 47 Tuc and of several giants in ω Cen. The results were obtained in collaboration with M. S. Bessell and K. C. Freeman, and will be fully reported in papers being prepared for submission to Astrophysical Journal. Most emphasis will be placed on 47 Tuc, where we have sought to address four problems. (i) How widespread are the CN anomalies reported by McClure and Osborn (1974), Bell, Dickens, and Gustafsson (1975), and Hesser, Hartwick, and McClure (19 77) - both throughout the HR diagram and in relative frequency? (ii) Is there any correlation between the relative frequency of the CN anomaly with radial position in the cluster, which might correlate with the color gradients observed by Gascoigne and Burr (1956) and Chun (1976)? (iii) Is there any evidence for G-band variations similar to those found generally in the metal poor ([Fe/H]< −1) globular clusters? (cf. Zinn 1973, 1977; Mallia 1975; Norris and Zinn 1977) (iv) Are the CN variations accompanied by variations in the abundance of the heavy elements?

Type
Part IV: HR Diagrams, Clusters
Information
Symposium - International Astronomical Union , Volume 80: The HR Diagram , 1978 , pp. 195 - 204
Copyright
Copyright © Reidel 1978 

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