Disk locking and the presence of slow rotators among solar-type stars in young star clusters

The simultaneous presence of both the so-called ultrafast rotators and slowly rotating stars among the solar-type stars (similar to0.6-1.2 M.) in the same young star clusters has been a puzzle in the field of stellar rotation. No model to date has been able to explain both by a single mechanism intrinsic to the star, and questions about the appropriate initial conditions for models often complicate the problem. In this paper, using the same starting conditions for the models that we used in examining the origin of the ultrafast rotators in young star clusters, we show that the slowest rotators demand an extrinsic mechanism. Assuming that this mechanism is a disk-star interaction, we determine that a disk-locking timescale of a few Myr must operate for this type of star. If, instead of allowing (radial) differential rotation, we enforce solid-body rotation, the models require timescales about 2-3 times as long.