Wave amplification in line-driven winds.

An analytical investigation of line scattering in perturbed stellar winds is carried out to study the effects of the diffuse radiation field on the instability of line-driven winds. The work represents an attempt to improve previous models which neglected the dynamical effects of the line-scattered photons. Consideration is focused on disturbances in P Cygni line formation in expanding circumstellar envelopes and limited to short wavelengths in radial propagation in the rapidly expanding part of the outflow. Resonance lines are determined to have no effect on the stability of fast acceleration zones and to contribute stability to outer wind regions. The lack of resonance effects produces a significant downward revision in estimates of growth rates and in the amount of instability in line-driven stellar winds.