Stellar rotation and disks in the orion nebula cluster

The new Wide Field Imager attached to the MPG/ESO 2.2 m telescope on La Silla, Chile, has been used to monitor 2000 stars in the Orion Nebula Cluster (ONC) at 815 nm on 45 nights between 25 Dec 1998 and 28 Feb 1999. Over 400 periodic variables have been found, most or all of which are rotating, spotted T Tauri stars (TTS), more than doubling the number of known rotation periods for cluster members. Masses and ages are available for 335 of these from the literature. We confirm the existence of a bimodal period distribution for stars with M > 0.25 M-circle dot. A surprising new result is that stars of lower mass tend to rotate faster than higher mass stars, perhaps indicating that their disks have dissipated more rapidly in the harsh cluster environment. In the mass range 0.1 - 1 M-circle dot between 40% and 80% of the stars have the variability characteristics of weak-line TTS (WTTS), suggesting that the halflife for accretion disks is similar to 1 Myr in this cluster and probably even smaller for the lower mass stars.