On the Relationship Between Stellar Rotation and Radius in Young Clusters

We examine the early angular momentum history of stars in young clusters via 197 photometric periods in the Orion Flanking Fields, 83 photometric periods in NGC 2264, and 256 measurements of v sin i in the ONC. We show that PMS stars, even those without observable disks, apparently do not conserve stellar angular momentum as they evolve down their convective tracks, but instead evolve at nearly constant angular velocity. This result is inconsistent with expectations that convective stars lacking disks should spin up as they contract, but paradoxically consistent with disk-locking models. We briefly explore possible resolutions, including disk locking, birthline effects, stellar winds, and planetary companions. We have found no plausible explanations for this paradox.