Evolution of massive stars: main sequence and close to it

Abstract

We discuss the status of current models for the early evolutionary stages of stars in the initial mass range 10-40 M Q . Effects of the pre-main sequence evolution, mass loss, internal mixing, and changes in atomic and nuclear data are outlined and confronted with several basic observational facts, which are unexplained by standard models. We conclude that especially internal mixing processes deserve much more attention in future investigations, and we show why convective mixing may be less efficient than generally assumed, but more mixing should be present in the radiative zones of at least a fraction of all massive stars.