SIMBAD references

The main sequence evolution of massive stars is calculated under the assumption that an unspecified mixing process were able to keep the models homogeneous during some fraction of the core hydrogen burning phase. The mixing could be due to rotation. The results are used to discuss discrepancies in stellar parameters between recent spectral analyses of OB stars and standard stellar evolution theory. The observed surface helium abundances serve as input to determine the duration of the mixing. It is shown that mixing on the main sequence alone cannot explain the derived values, although the agreement becomes much better when using the tracks presented here.