gas (Lucy & Abbott 1993, Springmann 1994, Gayley 1995, de Koter et al. 1997). This combined effect of ionization stratification and multiple line scattering leads to predictions for the ratio of wind momentum over radiative momentum , $\eta = {\mbox{$\dot{M}$}}{\mbox{$v_{\infty}$}}/ (L/c)$, of up to a factor of 10 – alleviating the wind momentum problem (but see Brown et al. 2004).

Last but not least, it appears that the “hot iron bump” (Fe [x]{} – Fe [xiv]{}) in the deep layers of WR stars has been identified as the initiation region of WR winds, conceptually proposed by Nugis & Lamers (2002), and most recently implemented numerically by Gräfener & Hamann (2005). These latter authors could self-consistently solve the dynamics for a carbon-rich WC5 star, thereby showing that radiation pressure is capable of initiating and maintaining the entire wind from below the photosphere to the region where the wind reaches its terminal velocity.

Now that it appears that radiation pressure is the principal driving mechanism for WR winds, we believe the time is ripe to explore the metallicity dependence of WR winds, as has previously been done for O stars (Vink et al. 2001, Kudritzki 2002). Empirically, the issue of an  ($Z$)-dependence 