The Variability and Rotation of Pre-Main-Sequence Stars in IC 348: Does Intracluster Environment Influence Stellar Rotation?

A variability study of the young cluster IC 348 at Van Vleck Observatory has been extended to a total of 7 yr. Twelve new periodic stars have been found in the last 2 yr, bringing the total discovered by this program to 40. In addition, we confirm 16 of the periods reported by others and resolve some discrepancies. The total number of known rotation periods in the cluster from all studies has now reached 70. This is sufficient to demonstrate that the parent population of K5-M2 stars is rotationally indistinguishable from that in the Orion Nebula Cluster, even though their radii are 20% smaller and they would be expected to spin about twice as fast if angular momentum were conserved. The median radius and therefore the inferred age of the IC 348 stars actually closely matches that of NGC 2264, but the stars spin significantly more slowly. This suggests that another factor besides mass and age plays a role in establishing the rotation properties within a cluster, and we suggest that it is environment. If disk locking were to persist for longer times in less harsh environments because the disks themselves persist for longer times, it could explain the generally slower rotation rates observed for stars in this cluster, whose earliest type star is of class B5. We have also obtained radial velocities, the first for pre-main-sequence stars in IC 348, and v sin i measurements for 30 cluster stars to assist in the study of rotation and as an independent check on stellar radii. Several unusual variable stars are discussed; in some or all cases their behavior may be linked to occultations by circumstellar material. A strong correlation exists between the range of photometric variability and the slope of the spectral energy distribution in the infrared. Nineteen of the 21 stars with I ranges exceeding 0.4 mag show infrared evidence for circumstellar disks.