---
author:
- 'Jorick S. Vink'
- Alex de Koter
title: 'On the metallicity dependence of Wolf-Rayet winds'
---

Introduction {#s_intro}
============

The physics of mass loss from massive stars is fundamental for a range of astrophysical issues, comprising the formation and evolution of individual massive stars, their final fate, in particular the nature of the compact object that is left behind (neutron star or black hole), as well as the input of energy, ionizing radiation, and chemical elements into the interstellar medium (ISM) of the host galaxy. There is growing evidence that long-duration gamma-ray bursts (GRBs) are the result of the collapse of a massive star (Galama et al. 1998, Hjorth et al. 2003). As these cosmological explosions are seen up to high redshift, and consequently at very low metal abundances, one needs to establish the $Z$-dependent properties of their progenitors, quite likely WR stars (e.g. Woosley et al. 1999). Furthermore, the observed properties of GRB are expected to depend on the history of the wind strength of the progenitor. The question that therefore needs to be addressed is: “are the winds of WR stars metallicity dependent?”

Although there are indirect indications for such a metallicity dependence (e.g. Hadfield 