1994A&A...290..819L

Based on recent progress in the theory of stellar structure and evolution, in the theory of stellar atmospheres and winds, and in the observational data base, we propose a new scenario for the evolution of very massive stars (M_ZAMS>40M_☉) in our Galaxy. A sample evolutionary calculation for a 60M_☉ star, incorporating recent theoretical results about violent pulsational instabilities in very massive stars, is critically compared with a multitude of observational facts. The relation between those pulsational instabilities and observed line profile variability in O stars is discussed. New wind models for PCygni are computed, with particular emphasis on the determination of its mass and surface He/H-ratio. A detailed comparison of our sequence with the Galactic WR population is performed, considering newly determined surface abundances. Our results suggest a new interpretation of luminous hydrogen-rich late-type WN stars as core hydrogen burning objects, while hot WN stars with small or zero hydrogen abundance are core helium burning stars. PCygni is identified with the hydrogen shell burning phase of our sequence. The observed upper luminosity limit for Galactic hydrogen-free WN stars appears to be consistent with our picture. Hence we propose the following evolutionary sequence for very massive stars: O -> Of -> H-rich WN -> LBV -> H-poor WN -> H-free WN -> WC -> SN.