MAGNETIC BRAKING OF G AND K-DWARFS WITHOUT CORE-ENVELOPE DECOUPLING

In the light of recent claims that conventional magnetic braking model s cannot explain the rotational evolution of the rapidly rotating G dw arfs in the alpha Persei and Pleiades clusters, we re-examine the brak ing problem within the simple framework of the Weber-Davis model with thermo-centrifugal wind acceleration. We find that the braking efficie ncy required to follow the evolution of individual stars from the age of the Pleiades to the age of the Sun and beyond is consistent with pr esent knowledge of the solar magnetic field strength, a simple linear dependence of the field strength on the inverse Rossby parameter, and a mass-loss rate that scales roughly as the square of the surface fiel d strength. Dynamo saturation at 15 to 45 times the present solar rota tion rate is required to explain the behaviour of the rapid rotators i n the young clusters, but there is no need to invoke exotic angular mo mentum loss mechanisms or core-envelope decoupling.