WN stars in the LMC: parameters and atmospheric abundances
W.-R. Hamann, L. Koesterke
The spectra of 18 WN stars in the Large Magellanic Cloud (LMC) are
quantitatively analyzed by means of "standard" Wolf-Rayet model
atmospheres, using the helium and nitrogen lines as well as the spectral
energy distribution. The hydrogen abundance is also determined. Carbon
is included for a subset of 4 stars. The studied sample covers all
spectral subtypes (WN2 ... WN9) and also includes one WN/WC transition
The luminosities of the program stars span a wide range (
L/Lsun = 5.0 ... 6.5). Due to the given LMC membership, these
results are free from uncertainties inferred from the distance. 50 % of
the studied stars (both, late and early WN subtypes) have rather low
luminosity (L/Lsun < 5.5). This puts tough constraints on
their evolutionary formation. If coming from single stars, it provides
evidence for strong internal mixing processes.
The empirical mass-loss rates are scaled down by a factor of about two
due to the impact of clumping, compared to previous studies adopting
homogeneous winds. There is no obvious strong correlation between the
mass-loss rates and other parameters like luminosity, temperature and
The stellar parameters for the present LMC sample are not systematically different from those of the Galactic WN stars studied previously with the same techniques, in contrast to the expected metallicity effects.
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