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K.E. Haisch, Jr., E.A. Lada (University of Florida), C.J. Lada (Harvard-Smithsonian CfA)
Young embedded clusters, widely believed to represent the birth places of the majority of stars in the Galaxy (ie. Lada 1992), provide unique opportunities for the study of the early phases of star formation and early stellar evolution in a statistically meaningful way. For example, the dense stellar environments and stellar contents (ie. the presence of O stars) in these clusters may affect the properties of circumstellar disks which are commonly thought to accompany the newly formed young stellar objects (YSOs). Since these disks represent the sites of any subsequent planet formation, determining the properties of disks in cluster environments is essential to evaluating the overall likelihood of planetary formation in the Galaxy.
We present the results of the first systematic near-infrared L (3.4 \mum) band survey of a statistically significant sample of YSOs in five young embedded clusters, Trapezium, NGC 2024, NGC 2071, NGC 2068 and IC 348, which span a range of environments, ages (\leq4 Myr) and stellar contents. From an analysis of the near-IR J (1.25 \mum), H (1.65 \mum), K (2.2 \mum) and L colors, we derive the IR excess fraction for each cluster and compare the results with the excess fractions obtained using only JHK colors. Assuming that these infrared excesses are produced by circumstellar disks, we determine the disk frequency as a function of cluster age and environment. In addition, we examine the robustness of the JHKL and JHK colors in identifying sources surrounded by circumstellar disks.