SPIN-DOWN OF RAPIDLY ROTATING, CONVECTIVE STARS

We construct a model for the spin-down of rapidly rotating. convective stars. We assume that rotation and convection cause a star to rotate differentially, that differential rotation and convection generate a magnetic dynamo, that a magnetic dynamo gives rise to mass loss and a magnetically controlled stellar wind, and that such a wind results in angular momentum loss and hence stellar spin-down. Using the model, we show that a protostar accreting from a circumstellar disc reaches an equilibrium rotation period significantly below break-up. We also show that the spin-down rates we derive are consistent with those required to drive the orbital evolution of cataclysmic variables.