STRUCTURE AND EVOLUTION OF MASSIVE STARS - MIXING PROCESSES AND STELLAR EVOLUTION

We review some of the mixing processes that may influence the evolutio n of massive stars, such as penetrative convection, and put our emphas is on those which occur in the radiative envelope. There the main tran sport mechanisms are a thermally driven meridian circulation, which de parts significantly from the classical Eddington-Sweet description, to gether with turbulent motions generated by the differential rotation. This rotation-induced mixing will surround the convective core of such stars with a region of decreasing helium content, which may prevent s emi-convection from ever appearing; the extent of this region depends sensitively on the rotation rate. The results are compared with those obtained earlier by Mestel (1953). Work is in progress to verify wheth er stars which rotate sufficiently fast may be thoroughly mixed.