Stability analysis of strange-modes in hot massive stars with time-dependent convection

Abstract

Abstract We carry out a nonadiabatic analysis of strange-modes in hot massive stars with time-dependent convection (TDC). In the envelopes of such stars, convective luminosity is not so dominant as it is in the envelopes of stars on the redder side of the classical instability strip. Around the Fe opacity bump, however, convection contributes nonnegligibly to energy transfer. Indeed, we find that the instability of modes excited at the Fe bump is likely to be weaker with TDC as compared with the case of adopting the frozen-in convection (FC) approximation. But we confirm that unstable strange-modes certainly remain in hot massive stars even by taking into account TDC. We also examine properties of the strange-mode instability, which is related to destabilization of strange-modes without adiabatic counterparts. In this type of instability, a phase lag between density and pressure varies from 0° to 180° in an excitation zone, unlike the case of the κ-mechanism. In addition, we confirm by comparing two models with Z = 0 and Z = 0.02 that the dominance of radiation pressure is important for this type of instability.