On the origin of microturbulence in hot stars

We present results from the first extensive study of convection zones in the envelopes of hot massive stars, which are caused by opacity peaks associated with iron and helium ionization. These convective regions can be located very close to the stellar surface. The region in the Hertzsprung-Russel diagram in which we predict the convection zones and the strength of this convection is in good agreement with the occurrence and strength of microturbulence in massive stars. We further argue that convection close to the surface may trigger clumping at the base of the stellar wind of hot massive stars.