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K.E. Haisch Jr., E.A. Lada (Univ. of Florida), C.J. Lada (Harvard-Smithsonian CfA)
We have completed the first extensive program of L band (3.4 \mum) imaging surveys of eight young clusters. Such clusters are likely responsible for producing most of the stars in the Galaxy. The aims of this study were (1) to determine the circumstellar disk fraction in each cluster, (2) investigate the dependence of the disk fraction on cluster age and environment, and (3) determine the disk dissipation timescale, thus providing an evaluation of the overall likelihood and conditions of planet formation in the Galaxy.
The derived disk fractions in the youngest clusters lead us to suggest that the formation of disks is quite common in clusters and not dependent on environment (i.e., star formation in clusters vs. isolation). If no massive stars are present in clusters, we show that disks are not preferentially destroyed in the dense cluster environment. An examination of successively older clusters reveals that the overall disk fraction decreases with increasing cluster age. We show that the rate of the decline appears to be a function of stellar mass, with disks around massive stars having shorter lifetimes compared to disks around lower mass stars. Finally, we derive the disk dissipation timescale and discuss the implications of this timescale on the formation of planetary systems.
This work was supported by a Florida Space Grant Fellowship, ISO grant #961604, NSF grant AST 9733367 to the Univ. of Florida and an ADP (WIRE) grant NAG 5-6751.