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. Simi lar observations were obtained of a large nearby region off the cluste r and its associated molecular cloud. Comparison of these observations enabled us to estimate the size of the cluster population and investi gate the nature of is members. In the region of the cluster surveyed a t 2.2 mum (K), we detected more than 1,650 sources. After correcting f or background/foreground field stars we find that the cluster contains 360 (+/- 130) members. We find that the slope of the K luminosity fun ction 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 a pparent K magnitude of roughly 13.0-14.0. Both the slope and the turno ver in the luminosity function can be modeled with an underlying clust er mass function which is similar to the Miller-Scalo or local field s tar IMF, provided that a mass-luminosity relation appropriate for prem ain-sequence stars applies to the cluster population. From analysis of the JHK color-color diagrams of the cluster and control fields we fin d that approximately 170 sources observed toward the cluster have colo rs indicative of intrinsic excess infrared emission. Consequently, inf rared 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 classica l T Tauri stars and Herbig AeBe stars. Circumstellar disk models can a ccount for the colors of most of these sources. That circumstellar dis ks are inferred for such a large fraction of the cluster membership ar gues for disk lifetimes which are at least as long as the age of the c luster (i.e., 5 x 10(6) yr). Many of these stars are also characterize d by relatively large amounts of extinction and may be partially embed ded in the molecular cloud behind the cluster.