On the Eddington limit and Wolf-Rayet stars

¹ Geneva Observatory, Geneva University, 1290 Sauverny, Switzerland
e-mail: andre.maeder@unige.ch; georges.meynet@unige.ch; sylvia.ekstrom@unige.ch
² Centre de Recherche Astrophysique, École Normale Supérieure de Lyon, 46 allée d’Italie, 69384 Lyon Cedex 07, France
e-mail: cyril.georgy@ens-lyon.fr

Received: 25 October 2011
Accepted: 13 January 2012

Abstract

Aims. We examine some properties of stars evolving close to the classical Eddington limit for electron-scattering opacity, when these stars maintain a chemically homogeneous structure as a result of mixing and/or mass loss.

Methods. We consider analytical relations and models computed with the Geneva code.

Results. Homologous, chemically homogeneous stars evolving with a constant Eddington factor obey a relation of the form μ²M = const. This applies, for example, to Wolf-Rayet (WR) stars in stages without hydrogen. The value of the constant may depend on the metallicity, initial mass, evolutionary stage, and physical processes included in the considered homologous evolutionary sequence. An average value of the constant between 20 and 40 in solar units is consistent with the masses of Galactic WR stars.