Photometric studies of young stars in clusters: Rotation and disks

We report on photometric monitoring programs aimed at three extremely young clusters in the vicinity of the Sun: the Orion Nebula Cluster (ONC), IC 348, and NGC 2264. Rotation periods for more than 200 pre-main-sequence stars with masses between similar to 0.1 and 1 M-circle dot and ages between similar to 1 and 3 Myr have been discovered as a result of these programs, and this number will soon double. The distribution of rotation periods in IC 348 is indistinguishable from the ONC and the combined sample of stars with M > 0.25 is clearly bimodal with peaks near 2 days and 8 days. NGC 2264 is different, possibly because of a higher age. A correlation between infrared excess emission, indicative of an accretion disk, and corotation radius in units of the stellar radius is shown, which supports the canonical view that disk locking is an important phenomenon in the angular momentum evolution of stars. The half-life for disks based on our analysis is only similar to 1.3 Myr, which puts severe constraints on the time available for giant planet formation.