Andreas Sander, Wolf-Rainer Hamann, Helge Todt
[Abridged] [...] Aims: The stellar parameters and mass-loss rates of the
GalacticWC stars shall be established. These data shall provide the empirical
basis for studies of (i) the role of WC stars in the evolution of massive
stars, (ii) the wind-driving mechanisms, and (iii) the feedback of WC stars as
input for the chemical and dynamical evolution of galaxies. Methods: We analyze
the nearly complete sample of un-obscured Galactic WC stars, using optical
spectra as well as UV spectra if available. The observations are fitted with
theoretical spectra, using the Potsdam Wolf-Rayet (PoWR) model atmosphere code.
A large grid of line-blanked models has been established for the range of WC
subtypes WC4 - WC8, and smaller grids for the WC9 parameter domain. WO stars
and WN/WC transit types are covered as well using special models. Results:
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 visual. In the Hertzsprung-Russell
diagram, the WC stars reside between the hydrogen and the helium zero-age main
sequences, having luminosities L from 10^4.9 to 10^5.6 Lsun The mass-loss rates
scale very tightly with L^0.8. The two WO stars in our sample turned out to be
outstandingly hot (\approx200 kK) and do not fit into the WC scheme.
Conclusions: From comparing the empirical WC positions in the
Hertzsprung-Russell diagram with evolutionary models, and from recent supernova
statistics, we conclude thatWC stars have evolved from initial masses between
20 and 45 Msun. In contrast to previous assumptions, it seems that WC stars in
general do not descend from the most-massive stars. Only the WO stars might
stem from progenitors that have been more massive than 45 Msun initially.
View original:
http://arxiv.org/abs/1201.6354
No comments:
Post a Comment