Title: Momentum deposition on Wolf-Rayet winds: Nonisotropic diffusion with effective gray opacity
Abstract: view Abstract Citations (87) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Momentum Deposition in Wolf-Rayet Winds: Nonisotropic Diffusion with Effectively Gray Opacity Gayley, Kenneth G. ; Owocki, Stanley P. ; Cranmer, Steven R. Abstract We derive the velocity and mass-loss rate of a steady state Wolf-Rayet (WR) wind, using a nonisotropic diffusion approximation applied to the transfer between strongly overlapping spectral lines. Following the approach of Friend & Castor (1983), the line list is assumed to approximate a statistically parameterized Poisson distribution in frequency, so that photon transport is controlled by an angle-dependent, effectively gray opacity. We show the nonisotropic diffusion approximation yields good agreement with more accurate numerical treatments of the radiative transfer, while providing analytic insight into wind driving by multiple scattering. We illustrate, in particular, that multiple radiative momentum deposition does not require that photons be repeatedly reflected across substantial distances within the spherical envelope, but indeed is greatest when photons undergo a nearly local diffusion, e.g., through scattering by many lines closely spaced in frequency. Our results reiterate the view that the so-called 'momentum problem' of Wolf-Rayet winds is better characterized as an 'opacity problem' of simply identifying enough lines. One way of increasing the number of thick lines in Wolf-Rayet winds is to transfer opacity from saturated to unsaturated lines, yielding a steeper opacity distribution than that found in OB winds. We discuss the implications of this perspective for extending our approach to W-R wind models that incorporate a more fundamental treatment of the ionization and excitation processes that determine the line opacity. In particular, we argue that developing statistical descriptions of the lines to allow an improved effective opacity for the line ensemble would offer several advantages for deriving such more fundamental W-R wind models. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175441 Bibcode: 1995ApJ...442..296G Keywords: Momentum Transfer; Opacity; Plasma Diffusion; Stellar Envelopes; Stellar Mass Ejection; Stellar Winds; Wolf-Rayet Stars; Anisotropy; Flow Velocity; Line Spectra; Mass Flow Rate; Photon Density; Stellar Models; Astrophysics; DIFFUSION; STARS: MASS LOSS; STARS: WOLF-RAYET full text sources ADS |
Publication Year: 1995
Publication Date: 1995-03-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 81
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