Disk-Locking Regulates Stellar Rotation in Young Clusters: Insights from NGC 2264

Many young clusters possess extended main sequences, a phenomenon commonly ascribed to stellar rotation. However, the mechanism behind their very wide stellar rotation distributions remains unclear. A proposed explanation is that magnetic star-disk interaction can regulate stellar rotation, i.e., protostars with longer disk lifetimes will eventually evolve into slow rotators, and vice versa. To examine this hypothesis, we took the star forming region, NGC 2264, as a test bed. We have studied its high-mass pre-main-sequence and zero-age main-sequence stars. We found that on average, disk-less pre-main-sequence stars rotate faster than their disk-bearing counterparts. The stellar rotation distribution of its zero-age main-sequence stars is similar to evolved young clusters. We conclude that disk-locking may play a crucial role in the rotational velocity distribution of intermediate-mass early-type stars. We suggest that the observed wide stellar rotation distribution in many young clusters can occur in their early stages.