DIFFERENTIAL ROTATION, CIRCULATION AND TURBULENCE IN RADIATIVE ZONES OF STARS

We examine the steady state circulation and differential rotation in t he radiative zones of early-type stars, following Zahn's assumption of latitude-independent rotation. The formulation includes in a consiste nt way the turbulence produced by shear, and the rotational and barocl inic forces driving the circulation. The angular momentum transfer by the combined action of meridional circulation and turbulence results i n a differential rotation in the radiative zone. In its turn, the diff erential rotation causes the circulation (due to deviations from the s pherical symmetry) and turbulence (due to instabilities associated wit h the shear stresses). Numerical results are given for the steady stat e in a 20 M. main sequence star. The circulation flow is very weak nea r the surface, and mixing between the internal and surface layers is p ractically absent even at high rotation rates. However, during the ini tial stage of evolution before the steady state is reached, a fraction of matter from the deep layers can be transported to the surface.