is the effective temperature at the radius where the Rosseland optical depth equals 2/3. In our studies, we define the stellar radius  and effective temperature  slightly differently, namely at the point where the thermalization optical depth measured in the center of the photometric $V$ band (at 5555 Å) equals $1/\sqrt{3}$ (see Schmutz et al. 1990 and de Koter et al. 1996 for detailed discussions). We note that these two definitions are only marginally different.

If the mass-loss rate for Wolf-Rayet stars is a function of metal abundance, the stellar radius may be expected to depend on $Z$ as well, because it is the wind strength that determines the location of . This adds a complication to the investigation of the mass-loss dependence of Wolf-Rayet stars. Recent WC spectral analyses including line-blanketing show values for  in the range 57 – 110 kK (Dessart et al. 2000, Crowther et al. 2002, Gräfener et al. 2002) – i.e. in some case well below the expected $T_{\rm evol}$ – and large geometrical extensions of WC atmospheres. If we adopt a constant  and $R_{*}$ for all $Z$ models, we may find that we are comparing models with widely different . If, on the other hand, 