The Evolution of Rotating 15 M⊙ Stars

Theoretical evolutionary sequences have been generated with the YREC code for a 15 M⊙ star from the ZAMS to core helium exhaustion with a variety of physical assumptions, covering both rotating and non-rotating cases. The non-rotating models agree qualitatively with other models found in the literature. The addition of only rotational distortion has little effect on the models, while the full treatment of rotation results in additional mixing and theoretical tracks that are similar to models with small amounts of convective overshoot. Models which include only rotation have fair agreement with the observed main sequence surface rotation velocities, but rotate too rapidly during the post-main sequence phases. The addition of mass loss at the given rates helps this problem somewhat but does not appear to completely resolve it. Neither the non-rotating models nor the rotating models provide full agreement with the terminal-age main sequence band used by Maeder & Meynet (1987); this may be indicative that additional mixing processes are necessary or that a more recent TAMS, such as that of Stothers (1991), should be used.