1991). Nugis & Lamers (2000, 2002) argue that the only meaningful temperature, i.e. one that is independent on the wind strength, is the one that corresponds to the hydrostatic core, as computed in stellar evolution codes. Hence, Nugis & Lamers (2000) list effective core temperatures, termed $T_{\rm evol}$, well in excess of 100 000 K. Their luminosities are of the order of respectively  $\simeq$ 5.8 for WN stars, and  $\simeq$ 5.3 for WC stars.

Due to the large geometrical extent of Wolf-Rayet atmospheres the effective temperature cannot be unambiguously defined. Typically, two effective temperatures play a role, see e.g. Dessart et al. (2000) for WC stars, and Herald et al. (2001) for WN stars. The first is based on the total flux at the inner boundary radius  of the model, and is used to define the stellar luminosity $L_{*} = 4 \pi R_{*}^2
\sigma T_{*}^4$. We note that recent studies incorporating a self-consistent treatment of line blanketing, such as for instance that of Herald et al. (2001) for the WN8 star WR40, tend towards smaller core radii and larger . This has led to a present-day luminosity of = 5.6 for this object. The second temperature that is frequently used 