WC stars and their role in the life cycle of massive stars
Andreas Sander, Wolf-Rainer Hamann
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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