Nonradial Pulsations in ε Persei

Abstract

We consider the question of whether all the modes detected in the line profile variations of Persei are consistent with nonradial pulsations excited by the kappa mechanism at the opacity Z-bump. We have computed massive (12.5-14 M☉) main-sequence models, adjusting the parameters such that the evolutionary tracks pass around the approximate position of Per on the H-R diagram. A linear nonadiabatic, nonradial pulsation analysis is applied to these models. The periods in the frame corotating with the stellar surface for the observed 2.3-4.5 hr modes are found to be consistent with the Z-bump kappa mechanism. We have found, however, that the longest-period mode (8.48 hr in the observer's frame) cannot be explained by the kappa mechanism. We have examined the effect of rotation on the stability of oscillations and found that the stabilizing effect is weak, so that only a few of the shortest-period modes are stabilized for the rotation speed of Per. No significant difference is found between prograde and retrograde modes in the stability. It is a puzzle why no retrograde mode has been detected in Per, which should equally be excited by the kappa mechanism. We also discuss the observed and theoretical line profile variations of Per in the Appendix.