Astron. Astrophys. 333, 956-969 (1998)

Clumping-corrected mass-loss rates of Wolf-Rayet stars

T. Nugis ¹, P.A. Crowther ² and A.J. Willis <sup>2

1</sup> Tartu Astrophysical Observatory, EE-2444 Tõravere, Estonia
² Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK

Received 2 September 1997 / Accepted 23 January 1998

Abstract

Mass-loss rates of Galactic Wolf-Rayet stars have been determined from their radio emission power and spectral index (), accounting for the clumped structure and (potential) variable ionization in their outer winds. The average spectral index between mm- and cm- wavelengths is 0.77 for WN stars and 0.75 for WC stars, in contrast with 0.58 expected for smooth winds. The observed wavelength dependence of can be explained using clumped wind models in some cases, with shocks (at 30-100 stellar radii) producing a higher ionization zone in the outer wind.

We obtain an empirical formula relating mass-loss with observed optical emission line equivalent widths, with application to stars without measured radio fluxes. Clumping-corrected mass-loss rates are generally lower than those obtained by current smooth wind models. Specifically we find log  (clumpy)-log  (smooth)=-0.19 ( =0.28) for WN stars, and log  (clumpy)-log  (smooth)=-0.62 ( =0.19) for WC stars. New mass-loss rate estimates agree very well with (clumping independent) determinations of WR components in binary systems.

Key words: stars: atmospheres stars: mass-loss stars: Wolf-Rayet radio continuum: stars

Send offprint requests to: T. Nugis

© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

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