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A&A 392, 653-669 (2002)
DOI: 10.1051/0004-6361:20020941
Stellar and wind properties of LMC WC4 stars
A metallicity dependence for Wolf-Rayet mass-loss rates
P. A. Crowther1, L. Dessart1, 2, D. J. Hillier3, J. B. Abbott1 and A. W. Fullerton4, 51 Department of Physics & Astronomy, UCL, Gower Street, London WC1E 6BT, UK
e-mail: jba@star.ucl.ac.uk
2 Sterrenkundig Institut, Universiteit Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands
e-mail: L.Dessart@astro.uu.nl
3 Department of Physics & Astronomy, University of Pittsburgh, 3941 O'Hara Street, PA 15260, USA
e-mail: jdh@phyast.pitt.edu
4 Dept. of Physics & Astronomy, University of Victoria, PO Box 3055, Victoria, BC, V8W 3P6, Canada
5 Department of Physics & Astronomy, Johns Hopkins University, 3400 North Charles St., Baltimore, MD 21218, USA
e-mail: awf@pha.jhu.edu
(Received 14 May 2002 / Accepted 21 June 2002 )
Abstract
We use ultraviolet space-based (FUSE, HST) and optical/IR
ground-based
(2.3 m MSSSO, NTT) spectroscopy
to determine the physical parameters of six WC4-type Wolf-Rayet stars in the
Large Magellanic Cloud.
Stellar parameters are revised significantly relative to
Gräfener et al.
(1998)
based on improved observations and more sophisticated model atmosphere codes,
which account for line blanketing and clumping.
We find that stellar luminosities are revised upwards by up to 0.4 dex, with
surface abundances spanning a lower range of
0.1
C/He
0.35 (20-45% carbon by mass) and O/He
0.06
(
10% oxygen by mass).
Relative to Galactic WC5-8 stars at known
distance, and analysed in a similar manner, LMC WC4 stars
possess systematically higher stellar luminosities,
~0.2 dex lower wind densities, yet a similar range
of surface chemistries. We illustrate how the classification
C III
5696 line
is extremely sensitive to wind density, such that this is
the principal difference
between the subtype distribution of LMC and Galactic early-type WC
stars. Temperature differences do
play a role, but carbon abundance does not
affect WC spectral types.
We illustrate the effect of varying temperature and mass-loss rate
on the WC spectral type for
HD 32257 (WC4, LMC) and HD 156385 (WC7, Galaxy) which
possess similar abundances and luminosities.
Using the latest evolutionary models, pre-supernova
stellar masses in the range 11-19
are anticipated for
LMC WC4 stars, with 7-14
for Galactic WC stars with known distances.
These values are consistent with pre-cursors of
bright type-Ic supernovae such as SN 1998bw (alias GRB 980425) for which
a minimum total mass of C and O of 14
has been independently
derived.
Key words: stars: Wolf-Rayet -- stars: fundamental parameters -- stars: evolution -- stars: abundances -- galaxies: Magellanic Clouds
Offprint request: P. A. Crowther, pac@star.ucl.ac.uk
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