INSTABILITIES IN LINE-DRIVEN STELLAR WINDS .5. EFFECT OF AN OPTICALLY THICK CONTINUUM

We extend our earlier analyses of the linear instability of line-driven stellar winds to the case, relevant to Wolf-Rayet stars, in which the continuum remains optically thick well above the sonic point. We find that an optically thick flow driven by pure scattering lines is stabilized by the drag effect of the diffuse, scattered radiation. However, even a relatively small photon destruction probability epsilon can cause a flow with continuum optical thickness tau-c >> 1 to remain unstable, with a growth rate of epsilon-tau-c-omega*, where omega* is the usual large growth rate that applies in the outer, optically thin part of the wind. The implications of these results for the variability characteristics of winds from Wolf-Rayet stars are briefly discussed.