Stability Analysis of Strange-Modes in Hot Massive Stars with Time-Dependent Convection

TL;DR

This study investigates the stability of strange-modes in hot massive stars considering time-dependent convection, revealing that these modes remain unstable even with convection effects included, and highlighting the role of radiation pressure.

Contribution

It provides the first nonadiabatic analysis of strange-modes with TDC in hot massive stars, showing their persistence and detailed properties under realistic conditions.

Findings

Strange-modes are unstable even with TDC.

Convection suppresses some mode instabilities but not all.

Radiation pressure dominance influences strange-mode instability.

Abstract

We carry out a nonadiabatic analysis of strange-modes in hot massive stars with time-dependent convection (TDC). In envelopes of such stars, convective luminosity is not so dominant as that in envelopes of stars in the redder side of the classical instability strip. Around the Fe opacity bump, however, convection non-negligibly contributes to energy transfer. Indeed, instability of modes excited at the Fe bump is likely to be suppressed with TDC compared with the case of adopting the frozen-in convection approximation. But we make sure that unstable strange-modes certainly appear 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, the phase lag between density and pressure varies from 0 to $180^{\circ}$ in an excitation zone unlike the case of the $\kappa$-mechanism. In addition, we confirm by comparing models with $Z=0$ and $Z=0.02$ that dominance of radiation pressure is important for this type of instability.