2006MNRAS.368L..57T

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 κ mechanism operating on an opacity bump at an envelope temperature of logT~ 6.25. This `deep opacity bump' is due primarily to L-shell bound-free transitions of iron. Periods of the unstable modes span ∼11-21h in the model containing some hydrogen, and ∼3-12h 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.