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I. B. Mihaylov, J. E. Bjorkman (The University of Toledo)
The wind momentum problem in Wolf-Rayet stars has been known for many years. The problem is that the observed radial momentum of the wind greatly exceeds the available photon momentum flux. The resolution of the problem requires that each photon be scattered many times. To do so requires a large number of lines (several per v\infty) distributed across the spectrum. Using a realistic line list, Lucy & Abbott (1993) have shown that the necessary global momentum deposition can indeed be achieved when one accounts for the multiple scatterings. However, Springman & Puls (1998) investigated the local momentum deposition and found that there was a deficit close to the star with a corresponding excess at large radii. The reason for the inconsistency is that the Lucy & Abbott method imposes a velocity law with v\infty taken form observations.
Here we present a method for solving the time independent wind equations by combining the Lucy & Abbott Monte Carlo radiation transfer technique (which accounts for multiple scattering) with the wind critical point equations. Thus we solve self-consistently for the mass loss rate and velocity vs. radius by measuring the local momentum deposition with our radiation transfer code. To test our method, we use a synthetic line list with lines chosen according to the CAK parameterization. We then demonstrate that our method reproduces the analytic CAK solution.
Ultimately we will use our method to determine the self-consistent mass loss rate and terminal speed of line blanketed stellar winds. We will also study how velocity perturbations arising from instabilities in the wind change the line forces and hence the momentum deposition in expanding stellar atmospheres.
This work is supported by NSF Grant AST - 9819928.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.