Convective envelopes in rotating OB stars

Aims. We study the effects of rotation on the outer convective zones of massive stars. Methods. We examine the effects of rotation on the thermal gradient and on the Solberg-Hoiland term by analytical developments and by numerical models. Results. 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 M-circle dot 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.