THE SODIUM ALUMINUM-OXYGEN ANTICORRELATION IN OMEGA-CENTAURI AND OTHER CLUSTERS

We discuss abundances of O, Na, and Al, as a function of [Fe/H], together with their interrelationships, from a high-dispersion, high signal-to-noise analysis of a (biased) sample of 40 red giants in the chemically inhomogeneous cluster omega Centauri. Accompanying the well-established range in [Fe/H], which in our sample extends from -1.8 to -0.8, we find large variations of O, Na, and Al. At [Fe/H] similar to -1.5, for example, Delta[O/Fe] greater than or equal to 0.9, Delta[Na/Fe] similar to 0.6, and Delta[Al/Fe] similar to 1.1. More important, there are strong ([Na/Fe], [O/Fe]) and ([Al/Fe], [O/Fe]) anticorrelations, and a strong positive correlation between [Na/Fe] and [Al/Fe]. The simplest explanation of these relationships is that they are produced by evolutionary mixing effects as suggested by Denisenkov and Denisenkova in the context of earlier observations of this duster and elaborated upon by Langer, Hoffman, and Sneden for more normal ones. We comment on the importance of the relative sizes of the ranges of intracluster Na and Al variations as a possible diagnostic of putative mixing phenomena.