The Rotation Period Distribution of Pre–Main-Sequence Stars in and around the Orion Nebula

Abstract

We report rotation periods for 254 stars in an area 40' × 80' centered on the Orion Nebula. We show that these stars are likely members of the young (∼106 yr) Orion OBIc/d association. The rotation period distribution we determine, which is sensitive to periods 0.1 < P < 8 days, shows a sharp cutoff for periods P < 0.5 days, corresponding to breakup velocity for these stars. Above 0.5 days the distribution is consistent with a uniform distribution; we do not find evidence for a "gap" of periods at 4–5 days. We find signatures of active accretion among stars at all periods; active accretion does not occur preferentially among slow rotators in our sample. We find no correlation between rotation period and near-IR signatures of circumstellar disks. In addition, we show that the distribution of v sin i among stars in our sample bears striking resemblance to that of low-mass Pleiades stars. We discuss the implications of our findings for the evolution of stellar angular momentum during the pre–main-sequence phase. We argue that all stars in our sample must still deplete angular momentum by factors of roughly 5–10, if they are to preserve their v sin i distribution over approximately the next 100 Myr. We consider in detail whether our findings are consistent with disk-regulated stellar rotation. We do not find observational evidence that magnetic disk-locking is the dominant mechanism in angular momentum evolution during the pre–main-sequence phase.