The pulsational stability of Wolf-Rayet stars

Abstract

Representative radial and nonradial pulsational modes of five WR star models are calculated. In agreement with Maeder (1984), a hydrogen-free 50-solar-mass model, evolved from an original main-sequence 120-solar-mass model, has a pulsationally unstable radial fundamental mode. All radial overtones are stable in this model, as is typical of massive He stars pulsationally driven by the epsilon effect at their centers. For the other four models, all with some residual surface hydrogen, no radial modes are unstable. Further, no unstable g-type nonradial modes are found for any of the five models. The nonradial modes have large amplitudes outside of the convective core, where they might be expected to be driven by the epsilon mechanism in their hydrogen-burning shells. However, their stability suggests that nonradial pulsations do not contribute to the extreme mass-loss rates observed for WR stars. Radial pulsations can occur for the hot He core burning (WNE, WC, and WO) WR stars, and could possibly cause mass loss, but only very late in their evolution. 22 references.