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S. E. Dahm (California Institute of Technology)
An optical and near-infrared (NIR) photometric and spectroscopic survey of an age-selected sample of young clusters was undertaken to trace the evolution of low-mass stars as they emerge from their parental molecular clouds, dissipate their inner circumstellar disks, and contract toward the zero-age main sequence (ZAMS). With a median age of ~1 Myr, the low-mass population of the youngest cluster surveyed is dominated by classical T Tauri stars and embedded infrared sources. At 12.8 Myr, the most evolved cluster is devoid of natal gas and dust and its massive members have already pulled away from the ZAMS. Between these extrema of ages, cluster populations experience dramatic changes as remnant molecular gas disperses, star formation halts, and accretion activity subsides. The current paradigm of circumstellar disk evolution states that viscous accretion abates as planet formation, stellar winds, and accretion processes remove dust and gas from the inner disk. Based upon the decay of strong H\alpha emission and NIR excess, most (~90%) low-mass stars are found to disperse their inner disks rapidly, within 5 Myr. The presence of a small number of strong H\alpha emitters in more evolved clusters, however, suggests that a shallow tail of accretion activity may persist to ages of 10 Myr, even within densely populated environments. Support for this work was provided by NASA through the Graduate Student Researchers Program (GSRP), grant number NGT5-50466.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.