Rotational Velocities of Stars in Open Clusters: The Time Dependence Revisited

Abstract

Using well defined rotational velocity distributions of G-type stars in the Hyades + Praesepe and Pleiades clusters, we have reexamined the age dependence of stellar rotation. The shape of the Vsini distribution is an extremely sensitive function of the α index of the braking law (dV/dt = -AV^α). The comparison of Hyades + Praesepe and Pleiades observations favours the value α = 2. The Vsini distributions could not be reproduced with α = 3, the value corresponding to the so-called t^-1/2 law.