Multicomponent radiatively driven stellar winds -: III.: Radiative-acoustic waves in a two-component wind

We study the stability of isothermal two-component radiatively driven stellar winds to one-dimensional perturbations larger than the Sobolev length, and radiative-acoustic waves in such stellar winds. We perform linear perturbation analysis in comoving fluid-frames of individual components and obtain the dispersion relation in the common fluid frame. For high density winds the difference between velocities of both components is relatively small and the wind is stable for radiative-acoustic waves discovered originally by Abbott, in accordance with the previous studies of the one-component wind. However, for such high density winds we found new types of waves, including a special case of frozen-in wavy patterns. On the other hand, if the velocity difference between wind components is sufficiently large (for low density winds) then the multicomponent stellar wind is unstable even for large-scale perturbations and ion runaway occurs. Thus, isothermal two-component stationary solutions of the radiatively line-driven stellar wind with an abrupt lowering of the velocity gradient are unstable.