WC stars and their role in the life cycle of massive stars

Andreas Sander, Wolf-Rainer Hamann

Institut für Physik und Astronomie, Universität Potsdam, Germany

The spectral analysis of Wolf-Rayet stars requires the detailed model- ing of expanding stellar atmospheres in non-LTE. The Galactic WN stars have been comprehensively analyzed with such models already some years ago. With a similarly comprehensive study, we now analyzed the Galactic WC stars, using the the Potsdam Wolf-Rayet (PoWR) model atmosphere code. Stellar and atmospheric parameters have been derived for more than 50 Galactic WC and two WO stars, covering almost the whole Galactic WC population as far as the stars are single, and un-obscured in the vi- sual. From comparing the empirical WC positions in the Hertzsprung-Russell diagram with evolutionary models, and from supernovae statistics, we conclude that WC stars have evolved from initial masses between 20 and 45 Msun. Only the WO stars might originate from progenitors that have been initially more massive than 45 solar masses. In combination with our previous results from WN analyses, the empirical HRD indi- cates that stars with initial masses above 60 Msun generally do not reach the WC stage, but retain some of their hydrogen envelope thus appearing as a WNL star or LBV till they explode as a supernova.

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