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

Abstract

ABSTRACT We explore and extend the suggstion that 23Na might be produced in the interior of an evolving low-mass globular cluster giant and mixed to the surface (Kudryashov & Tutukov 1988, Denisenkov & Denisenkova 1990). The reaction rates alone show that sodium will be produced by proton captures on 22Ne in the region of a globulr cluster giant in which oxygen is being depleted. A more detailed calculation shows that significant amounts of the much more abundant 20Ne can be transformed into 23Na on somewhat longer timescales. Atmospheric oxygen depletions that are the result of very deep mixing are bound to be accompanied by sodium enhancements due to 22Ne(p,gamma)23Na reactions; they are quite likely to be accopanied by larger sodium enhancements that begin with proton captures on 20Ne. 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 27Al 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.