Convective envelopes in rotating OB stars

TL;DR

This paper investigates how rotation influences the convective zones in massive OB stars, revealing that rotation enhances equatorial convection and leads to the formation of multiple convective envelopes, which impacts stellar evolution.

Contribution

It provides analytical and numerical analysis showing rotation's significant effect on the thermal gradient and convection zones in OB stars, including the formation of multiple convective envelopes.

Findings

Rotation favors convection at the equator.

A rotating 20 Msun star can have two convective envelopes.

Rotation increases the thickness of convective zones from 4.6% to 13.2% of the stellar radius.

Abstract

We study the effects of rotation on the outer convective zones of massive stars. We examine the effects of rotation on the thermal gradient and on the Solberg--Hoiland term by analytical developments and by numerical models. Writing the criterion for convection in rotating envelopes, we show that the effects of rotation on the thermal gradient are much larger and of opposite sign to the effect of the Solberg-Hoiland criterion. On the whole, rotation favors convection in stellar envelopes at the equator and to a smaller extent at the poles. In a rotating 20 Msun star at 94% of the critical angular velocity, there are two convective envelopes, with the bigger one having a thickness of 13.2% of the equatorial radius. In the non-rotating model, the corresponding convective zone has a thickness of only 4.6% of the radius. The occurrence of outer convection in massive stars has many consequences.