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 kappa
mechanism operating on an opacity bump at an envelope temperature 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 hr in the model containing
some hydrogen, and ~ 3-12 hr 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 hr-periodic variation of WR 123 recently reported by Lefevre et al. (2005).Comment: 5 pages, 3 figures, accepted by MNRAS letter