Implications of the metallicity dependence of Wolf-Rayet winds

¹ Department of Physics and Astronomy, Queen's University Belfast, Belfast, BT7 1NN, Northern Ireland, UK e-mail: j.eldridge@qub.ac.uk
² Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire, ST55BG, UK e-mail: jsv@astro.keele.ac.uk

Received: 4 November 2005
Accepted: 6 March 2006

Abstract

Aims.Recent theoretical predictions for the winds of Wolf-Rayet stars indicate that their mass-loss rates scale with the initial stellar metallicity in the local Universe. We aim to investigate how this predicted dependence affects the models of Wolf-Rayet stars and their progeny in different chemical environments.

Methods.We compute models of stellar structure and evolution for Wolf-Rayet stars for different initial metallicities, and investigate how the scaling of the Wolf-Rayet mass-loss rates affects the final masses, the lifetimes of the WN and WC subtypes, and how the ratio of the two populations vary with metallicity.

Results.We find significant effects of metallicity dependent mass-loss rates for Wolf-Rayet stars. For models that include the scaling of the mass-loss rate with initial metallicity, all WR stars become neutron stars rather than black holes at twice the solar metallicity; at lower Z, black holes have larger masses. We also show that our models that include the mass-loss metallicity scaling closely reproduce the observed decrease of the relative population of WC over WN stars at low metallicities.