Stellar rotation: Evidence for a large horizontal turbulence and its effects on evolution

We derive a new expression for the coefficient of diffusion by horizontal turbulence in rotating stars. This new estimate can be up to two orders of magnitude larger than that given by a previous expression. As a consequence the differential rotation on an equipotential is found to be very small, which reinforces Zahn's hypothesis of shellular rotation. The role of the so–called μ–currents, as well as the driving of circulation, are reduced by the large horizontal turbulence. Stellar evolutionary models for a 20 star are calculated with the new coefficient. The new and large tends to limit the size of the convective core and at the same time it largely favours the diffusion of helium and nitrogen to the surface of rotating OB stars, a feature supported by recent observations.