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Astron. Astrophys. 348, L45-L48 (1999)

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Letter to the Editor

An explanation of observed trends in the X-ray emission from single Wolf-Rayet stars

R. Ignace and L.M. Oskinova

University of Glasgow, Kelvin Bldg, Department of Physics and Astronomy, Glasgow, G12 8QQ, Scotland UK

Received 10 May 1999 / Accepted 14 July 1999


The O and early B star winds show empirical correlations between X-ray ([FORMULA]) and Bolometric ([FORMULA] luminosity as well as wind properties such as wind momentum and wind kinetic energy. Wolf-Rayet stars do not. We discuss scaling relations to qualitatively explain this lack of correlation among the WR winds and to quantitatively reproduce the observed ratio of X-ray luminosities between the N-rich WN types and C-rich WC types. If (a) the filling factor of hot X-ray emitting gas varies as [FORMULA] for stars of different mass loss and terminal speed and (b) the ambient Wolf-Rayet wind component is optically thick to the hot gas X-rays, then a lack of correlation between [FORMULA] and wind parameters is to be expected. The emergent X-ray emission then depends only on factors relating to relative abundances and ionization. The observed ratio [FORMULA] is consistent with our scaling analysis using typical WN and WC abundances.

Key words: stars: abundances – stars: early-type – stars: mass-loss – stars: Wolf-Rayet – X-rays: stars

Send offprint requests to: rico@astro.gla.ac.uk

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999