INFRARED IMAGES OF THE YOUNG CLUSTER NGC-2264

We present the initial results of an extensive infrared imaging survey of the young cluster NGC 2264 and a nearby galactic control field. A large portion of the cluster was imaged in each of the three standard near-infrared colors (J, H, and K) with an infrared array camera. Similar observations were obtained of a large nearby region off the cluster and its associated molecular cloud. Comparison of these observations enabled us to estimate the size of the cluster population and investigate the nature of is members. In the region of the cluster surveyed at 2.2 mum (K), we detected more than 1,650 sources. After correcting for background/foreground field stars we find that the cluster contains 360 (+/- 130) members. We find that the slope of the K luminosity function of the cluster is significantly steeper than that expected for a cluster of ZAMS stars and appears to flatten out or turn over at an apparent K magnitude of roughly 13.0-14.0. Both the slope and the turnover in the luminosity function can be modeled with an underlying cluster mass function which is similar to the Miller-Scalo or local field star IMF, provided that a mass-luminosity relation appropriate for premain-sequence stars applies to the cluster population. From analysis of the JHK color-color diagrams of the cluster and control fields we find that approximately 170 sources observed toward the cluster have colors indicative of intrinsic excess infrared emission. Consequently, infrared excess stars appear to account for a relatively large fraction (50% +/- 20%) of the cluster membership. These stars have near-infrared colors similar to those of young emission-line stars such as classical T Tauri stars and Herbig AeBe stars. Circumstellar disk models can account for the colors of most of these sources. That circumstellar disks are inferred for such a large fraction of the cluster membership argues for disk lifetimes which are at least as long as the age of the cluster (i.e., 5 x 10(6) yr). Many of these stars are also characterized by relatively large amounts of extinction and may be partially embedded in the molecular cloud behind the cluster.