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Article overview
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Neglecting the porosity of hot-star winds can lead to an underestimation
of mass-loss rates | | L. M. Oskinova
; W.-R. Hamann
; A. Feldmeier
; | | Date: |
18 Apr 2007 | | Subject: | Astrophysics (astro-ph) | | Abstract: | Adequate stellar atmosphere models are required for spectral analyses and
mass-loss determinations of massive stars. Present models account for the
inhomogeneity of stellar winds only in the approximation of small-scale
optically thin clumps. Compared to previous homogeneous models, this treatment
has led to a reduction of empirical mass-loss rates by factors of two to three,
and even further reductions are presently discussed. We generalized the Potsdam
Wolf-Rayet (PoWR) model atmosphere code in the ``formal integral’’ in order to
account for clumps which are not necessarily optically thin . The stellar wind
is characterized by the filling factor of the dense clumps, and by their
average separation. Adopting a statistical distribution of clumps, an effective
opacity is obtained and applied for the radiative transfer. Our model shows
that wind porosity has a pronounced effect on the emergent spectrum. Modeling
for the O-type supergiant Zeta Puppis reveals that the optically thin H_alpha
line is not affected by wind porosity, but the PV resonance doublet becomes
significantly weaker when porosity is taken into account. In the case of
Wolf-Rayet stars we demonstrate for two representative models that stronger
lines are typically reduced by a factor of two in intensity, while very weak
lines remain unchanged by porosity effects with a plausible choice of the
clump-separation parameter. Therefore, in the case of Zeta Puppis, the reported
discrepancies between resonance-line and recombination-line diagnostics can be
entirely resolved with the models which include wind porosity, without a
downward revision of the mass-loss rate. As porosity effect reduces the
strength of spectral features, its neglection hitherto in stellar wind modeling
has potentially led to an underestimation of empirical mass-loss rates. | | Source: | arXiv, arxiv.0704.2390 | | Services: | Forum | Review | PDF | Favorites | |
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