Are Wolf-Rayet Stellar Winds Driven by Radiation Forces?

We derive a formal condition for an existence of a critical point in optically thick flows. Using recent synthetic quantitative spectroscopy results and recent OPAL opacities we find that Wolf-Rayet stars (of the WRC type and part of the WRN type) satisfy this condition, and we account for the observed mass-loss rates and inferred critical temperatures.

We also show that there is no obvious momentum problem well below the photosphere. A less quantitative discussion is given for critical points with low to moderate optical depth, where non-LTE effects are conjectured to be crucial.