DIFFERENTIAL ROTATION AND THE CONVECTIVE CORE MASS OF UPPER MAIN-SEQUENCE STARS

Accurate two-dimensional models of rotating main-sequence stars have b een computed to test the recently proposed hypothesis that stars with a uniform distribution of specific angular momentum have more massive convective cores and, therefore, longer lifetimes than their rigidly r otating and nonrotating counterparts. The main conclusion is that the numerical models do, indeed, confirm this hypothesis at least for star s with masses below 12 M.. Hence, this phenomenon provides yet another possible explanation for intermediate mass blue stragglers and other peculiar stars that may arise from enhanced core-envelope mixing. In m ore massive configurations, the radiative temperature gradient at the core boundary also increases with an increase in rotation (as in the l ower masses) but the adiabatic gradient increases by an even larger am ount due to a drop in the radiation pressure. Thus, the convective cor es of rotating massive stars always decrease in mass fraction for any distribution of angular velocity.