Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem

We compare the angular momentum extracted by a wind from a pre-main-sequencestar to the torques arising from the interaction between the star and itsKeplerian accretion disk. We find that the wind alone can counteract thespin-up torque from mass accretion, solving the mystery of why accretingpre-main-sequence stars are observed to spin at less than 10% of break-upspeed, provided that the mass outflow rate in the stellar winds is ~10% of theaccretion rate. We suggest that such massive winds will be driven by somefraction $\epsilon$ of the accretion power. For observationally constrainedtypical parameters of classical T-Tauri stars, $\epsilon$ needs to be between afew and a few tens of percent. In this scenario, efficient braking of the starwill terminate simultaneously with accretion, as is usually assumed to explainthe rotation velocities of stars in young clusters.Comment: Accepted by ApJ Letter