SODIUM OXYGEN ABUNDANCE ANTICORRELATIONS AND DEEP-MIXING SCENARIOS FOR GLOBULAR-CLUSTER GIANTS

We explore and extend the suggestion that Na-23 might be produced in the interior of an evolving low-mass globular-cluster giant and mixed to the surface (Kudryashov and Tutukov 1988; Denisenkov and Denisenkova 1990). The reaction rates alone show that sodium will be produced by proton captures on Ne-22 in the region of a globular-cluster giant in which oxygen is being depleted. A more detailed calculation shows that significant amounts of the much more abundant Ne-20 can be transformed in Na-23 on somewhat longer time scales. Atmospheric oxygen depletions that are the result of very deep mixing are bound to be accompanied by sodium enhancements due to Ne-22 (p,gamma) Na-23 reactions; they are quite likely to be accompanied by larger sodium enhancements that begin with proton captures on Ne-20. One cannot argue that a Na-O anticorrelation is strong evidence for a primordial account of the observed variations in O and Na. We find that Al-27 can also be produced by very deep mixing and that the aluminum enhancements that would result are likely to be smaller than the sodium enhancements. Finally, we suggest a number of ways in which the consequences of this sort of very deep mixing might be distinguished from primordial variations in oxygen, sodium, and aluminum.