Rotational evolution of young stars: IC 348 and NGC 2362

Evolution of young stars' rotation is investigated by using evolutionary tracks considering conservation of angular momentum and simulations of disk-locking. By assuming that the disk-locking mechanism prevents the expected spin up in the pre-main sequence, we used rotating evolutionary models and observational data to constraint disk lifetimes and locking periods of low-mass stars in the young clusters IC 348 and NGC 2362. We aim at understanding the rotational period distributions of these clusters' stars,
which are known to be bimodal and dichotomic. The evolution is assumed to occur with conservation of angular momentum
for fast rotators and a constant angular velocity before spinning up to the ZAMS for moderate rotators. We generated sets of evolutionary tracks and estimated a mass and an age for all stars. We found a mean age of 2.5 Myr for IC 348 and 3.3 Myr for NGC 2362. Most of stellar masses were found to be in the ranges of 0.1-0.8 M$_{\odot}$ for both clusters. In order to investigate the disk-locking effects in these stars, two hypotheses were tested and compared with observational disk indicators available in the literature. In hypothesis 1, we considered that peaks at longer periods in the period distribution are formed by stars with angul
ar velocities locked to a circumstellar disk. Hypothesis 2 considers that rotation period distributions of both clusters were
similar to that of Orion Nebula Cluster (ONC) when they had, on average, the same age as the ONC (1 Myr). This scenario implies that some of stars of IC 348 and NGC 2362 were kept locked in their disks during their first million years, and, after that, they evolved conserving their angular momentum. We, then, simulated period distributions for IC 348 and NGC 2362 at about 1 Myr and obtained that they were similar to that of ONC. Our results favor hypothesis 2 and indicate that the disk-locking mechanism seems to operate in young stars with a locking period of about 8 days during a mean disk lifetime of about 1-1.5 Myr.