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Paper: Astrophysical Observations of Disk Evolution around Solar Mass Stars
Volume: 341, Chondrites and the Protoplanetary Disk
Page: 131
Authors: Hartmann, L.
Abstract: I review some astrophysical constraints on the evolution of protoplanetary disks. In general, infrared excesses due to dusty disks disappear over timescales of 1-10 Myr; about half of all systems exhibit no detectable near-infrared disk emission at ages of 1-2 Myr. The disappearance of near-infrared dust emission corresponds very well with the cessation of accretion of material onto the central star. Whether this corresponds to the removal of small dust particles throughout the disk, or only such removal in inner disks (within about 1 AU), is not entirely clear, but there are examples of systems with substantial outer disks which have evacuated inner holes. I present new direct evidence that dust evolution is faster in inner disks at ages of roughly 3 Myr, as expected on general theoretical grounds. Our understanding of gas content in disks is very poor, given the high optical depths of strong lines and the lack of good diagnostics for cold molecular hydrogen. The statistical constraint that disk gas reservoirs must be large enough to account for accretion rates during the T Tauri phase indicates that disk gas masses must be at least 0.01 MSolar at ages of ~ 1 Myr. Although most of our studies of disks have been in regions of low stellar density, and most stars are born in clusters, there is new evidence that disk evolution may not be very much different for most stars located within typical young star clusters in the solar neighborhood.
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