Abstract
Observations reveal that the rotational velocities of young low mass stars differ significantly depending on whether or not they show accretion disk signatures. Slower rotational velocities are found for those stars apparently surrounded by accretion disks suggesting that the disk may play a fundamental role in regulating the angular velocity of the central star, countering the tendency of the star to spin up both from contraction toward the main sequence and from accretion of disk material of high specific angular momentum. This would imply that the initial angular momentum of a forming star is the angular momentum it carries when its accretion disk is dissipated. The observed order of magnitude range in rotational velocities among ZAMS stars of a given mass in young clusters might then result in part from a range in timescales for disk dissipation: stars which lost their disks early would be among the most rapid rotators, while those which retained their disks the longest would populate the low velocity end of the ZAMS rotational velocity distribution.
