*Astron. Astrophys. 335, 1003-1008 (1998)*
## Spectrum formation in clumped stellar winds:
consequences for the analyses of Wolf-Rayet spectra
**
W.-R. Hamann and
L. Koesterke
**
Lehrstuhl Astrophysik, Universität Potsdam, Am Neuen
Palais 10, D-14469 Potsdam, Germany
(wrh@astro.physik.uni-potsdam.de)
*Received 6 March 1998 / Accepted 20 April 1998*
**Abstract**
Inhomogeneous Wolf-Rayet type stellar winds are modeled in a
first-order approximation, assuming that small-scale clumps are
distributed with a constant volume filling factor within an interclump
space which is void. Model calculations as well as analytical
considerations show that the main spectral features, i.e. the strength
of the emission lines, are approximately invariant if the enhanced
density in the clump medium is compensated by a suitable scaling of
the mass-loss rate. Hence, to the first order the mass-loss rate is
the only empirical parameter which is affected by the application of
clumped models for spectral analyses.
In clumpy atmospheres the electron-scattering line wings become
weaker than in homogeneous models. This effect can be used to
determine the degree of clumping empirically. We select Wolf-Rayet
stars of different spectral subclasses and compare their spectra with
adequate models, varying the clumpiness. In all cases, the homogeneous
model can be definitely ruled out because it predicts electron
scattering wings that are significantly stronger than observed. If the
clumps fill 1/4 of the volume, the line wings are in reasonable
agreement, while for a filling factor of 1/16 the wings are possibly
too shallow, but still compatible with the observation within the
error margin. Adopting a filling factor of 1/4 (i.e. the density in
the clumps is enhanced by a factor of four, compared to a smooth model
with same mass-loss rate) as a typical value, the empirical mass-loss
rates become smaller by a factor of two than obtained with homogeneous
models.
**Key words:** radiative
transfer
stars:
atmospheres
stars: fundamental
parameters
stars: mass
loss
stars: Wolf-Rayet
*Send offprint requests to:* W.-R. Hamann
SIMBAD Objects
### Contents
© European Southern Observatory (ESO) 1998
Online publication: June 26, 1998
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