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Astron. Astrophys. 337, 223-232 (1998)


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Inference of steady stellar wind [FORMULA] laws from optically thin emission lines

III. Inversion of total line intensity distributions

R. Ignace 1, J.C. Brown 1, J.E. Milne 1 and J.P. Cassinelli 2

1 Department of Physics and Astronomy, University of Glasgow, Glasgow, UK
2 Department of Astronomy, University of Wisconsin-Madison, USA

Received 26 February 1998 / Accepted 15 May 1998

Abstract

The variation with wavelength for a sequence of total intensities of stellar wind lines is considered as a basis for deriving the wind velocity law [FORMULA]. In particular, we focus on the case where the continuum formation in the wind is dominated by the free-free opacity so that the inner radius increases with wavelength, as is realized in some massive winds like those of the Wolf-Rayet stars. The line emission in the wind occurs exterior to the continuum photosphere, hence lines observed at different wavelengths probe different regions of the wind acceleration. A major consequence of these physical conditions is the opportunity to infer [FORMULA], even if non-monotonic. Numerical examples are given to test the method, in which smooth and non-smooth monotonic [FORMULA], non-monotonic [FORMULA], and the effects of noise are addressed. In the absence of noise, the inversion of the simulated data for radius [FORMULA] and expansion velocity [FORMULA] is excellent. Even with noise at the 15% level, the recovery for [FORMULA] remains reasonably robust, though the results for [FORMULA] are more strongly affected. Although more sophisticated techniques are required to infer [FORMULA] from noisy data, the simpler considerations presented here provide a basic theoretical framework for applying the inversion and indicate the potential of the method for deriving the wind flow structure.

Key words: line: profiles – stars: early-type – stars: mass-loss – stars: Wolf-Rayet

Send offprint requests to: R. Ignace

© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998

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