Spectral analyses of Wolf-Rayet winds
W.-R. Hamann, L. Koesterke and G. GräfenerUniversität Potsdam, Institut für Physik, Lehrstuhl Astrophysik
Postfach 601553, D-14415 Potsdam, Germany
The analysis of Wolf-Rayet spectra requires adequate model atmospheres
which treat the non-LTE radiation transfer in a spherically expanding
medium. Present state-of-the-art calculations account for complex model
atoms with, typically, a few hundred energy levels and a few thousand
spectral lines of He and CNO elements. In the most recent version of our
model code, blanketing by millions of lines from iron-group elements is
These models have been widely applied for the spectral analysis of WN
stars in the Galaxy and LMC. WN spectra can be well reproduced in most
cases. WC stars have not yet been analyzed comprehensively, because
the agreement with observations becomes satisfactory only when
line-blanketed models are applied.
The introduction of inhomogeneities (clumping), although treated in a
rough approximation, has significantly improved the fit between
synthetic and observed spectra with respect to the electron-scattering
wings of strong lines. The mass-loss rates obtained from spectral
analyses become smaller by a factor 2-3 if clumping is accounted for.
A pre-specified velocity law is adopted for our models, but the radiation pressure can be evaluated from our detailed calculation and can be compared a posteriori with the required wind acceleration. Surprisingly we find that the line-blanketed models are not far from being hydrodynamically consistent, thus indicating that radiation pressure is probably the main driving force for the mass-loss from WR stars.
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