Stellar Convection Theory

Abstract

This meeting, which deals with turbulence in stars, opens with a review on thermal convection. There is no better way to state from the start that among all instabilities that are likely to arise in stars, it is thermal convection which is the most firmly established as a cause for the turbulence that we observe on their surface. Our confidence in this comes mainly from the theoretical prediction that convective instability sets in whenever the density stratification becomes superadiabatic, as is expected in late type stars whose outer layers are very opaque, due to the ionization of the two most abundant elements, hydrogen and helium. And, in these stars at least, thermal convection occurs close enough to the photosphere to influence, be it indirectly, the profile of spectral lines.