NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Momentum deposition on Wolf-Rayet winds: Nonisotropic diffusion with effective gray opacityWe 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 potons 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 identfying 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.
Document ID
19950054923
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Gayley, Kenneth G.
(Univ. of Delaware, Newark, DE United States)
Owocki, Stanley P.
(Univ. of Delaware, Newark, DE United States)
Cranmer, Steven R.
(Univ. of Delaware, Newark, DE United States)
Date Acquired
August 16, 2013
Publication Date
March 20, 1995
Publication Information
Publication: The Astrophysical Journal, Part 1
Volume: 442
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A86522
Funding Number(s)
CONTRACT_GRANT: NSF AST-91-15136
CONTRACT_GRANT: NAG5-1657
CONTRACT_GRANT: NAGW-2624
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available