Excitation of g modes in Wolf-Rayet stars by a deep opacity bump

Abstract

We examine the stability of ℓ= 1 and ℓ = 2 g modes in a pair of nitrogen-rich Wolf-Rayet stellar models characterized by differing hydrogen abundances. We find that modes with intermediate radial orders are destabilized by a K mechanism operating on an opacity bump at an envelope temperature of log T ≈ 6.25. This 'deep opacity bump' is due primarily to L-shell bound-free transitions of iron. Periods of the unstable modes span ~11-21 h in the model containing some hydrogen, and ~3-12 h in the hydrogen-depleted model. Based on the latter finding, we suggest that self-excited g modes may be the source of the 9.8-h periodic variation of WR 123 recently reported by Lefèvre et al. © 2006 The Authors. Journal compilation © 2006 RAS.