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This paper reviews many of the properties relating to the chemical inhomogeneity of globular clusters. Three main types of anomalous stars are found within clusters: the CH stars, weak-G-band stars, and giants with enhanced CN bands. Of these, the CN-enhanced giants are the most common, while the CH stars are the rarest. A number of characteristics of these stars, including the relationship between the carbon and nitrogen abundances; correlations between CN enhancements and atomic line strengths; and the stellar luminosity dependence of C and N abundances, are discussed. The cluster Omega Cen not only contains all three types of the above-mentioned stars but also exhibits a much wider variety of abundance anomalies, including star-to-star iron-peak element variations and the presence of a radial CN gradient. A number of the characteristics of the Omega Cen inhomogeneity are described. Possible mechanisms for establishing internal cluster-abundance variations are summarized, and arguments for and against two of the most popular of these, the mixing and primordial-enrichment hypotheses, are discussed.
Graeme H. Smith (Sun,) studied this question.