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

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

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

1 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


Mass-loss rates of Galactic Wolf-Rayet stars have been determined from their radio emission power and spectral index ([FORMULA]), accounting for the clumped structure and (potential) variable ionization in their outer winds. The average spectral index between mm- and cm- wavelengths is [FORMULA] 0.77 for WN stars and [FORMULA] 0.75 for WC stars, in contrast with [FORMULA] 0.58 expected for smooth winds. The observed wavelength dependence of [FORMULA] 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  [FORMULA] (clumpy)-log  [FORMULA] (smooth)=-0.19 ([FORMULA] =0.28) for WN stars, and log  [FORMULA] (clumpy)-log  [FORMULA] (smooth)=-0.62 ([FORMULA] =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