Presupernova evolution of rotating massive stars. II. Evolution of the surface properties

We investigate the evolution of the surface properties of models for rotati ng massive stars, i.e., their luminosities, effective temperatures, surface rotational velocities, and surface abundances of all isotopes, from the ze ro-age main sequence to the supernova stage. Our results are based on the g rid of stellar models by Heger, Langer, & Woosley, which covers solar metal licity stars in the initial-mass range 8-25 M.. Results are parameterized b y initial mass, initial rotational velocity and major uncertainties in the treatment of the rotational mixing inside massive stars. Rotationally induc ed mixing processes widen the main. sequence and increase the core hydrogen -burning lifetime, similar to the effects of convective overshooting. It ca n also significantly increase the luminosity during and after core hydrogen burning, and strongly affects the evolution of the effective temperature. Our models predict surface rotational velocities for various evolutionary s tages, in particular for blue supergiants, red supergiants, and for the imm ediate presupernova stage. We discuss the changes of the surface abundances due to rotationally induced mixing for main sequence and post-main-sequenc e stars. We single out two characteristics by which the effect of rotationa l mixing can be distinguished from that of massive close binary mass transf er, the only alternative process leading to nonstandard chemical surface ab undances in massive stars. A comparison with observed abundance anomalies i n various types of massive stars supports the concept of rotational mixing in massive stars and indicates that it is responsible for most of the obser ved abundance anomalies.