Abstract
We develop a model for the rotational braking of late type dwarfs, assuming that it is only occurring in the outer convective envelope. Braking is caused by a magnetic torque acting at the corr6tation radius. We explore two circumstances; one in which braking is due to the mean global magnetic activity of the star, the other where it is caused by a number of localized active regions. We find that only the latter can describe the observed secular decay of the rotational velocity of solar type stars. On the other hand, from the observed relationships between the angular velocity and different indices of chromospheric and coronal activity, we can reproduce the observed behaviour of both types of activity as a function of the stellar mass for stars in the Pleiades and Hyades clusters.
