Lee HARTMANN : University of Michigan
Disc lifetimes as a function of environment and stellar mass
Recent observations with the Spitzer Space Telescope have yielded further insight into the question of disk lifetimes. The much higher sensitivity out to longer wavelengths has led to better-defined "disk frequencies". "Clearing", i.e. elimination of substantial infrared excess emission from small dust particles, seems to occur rather rapidly over a size scale of a few to 10 AU, and is accompanied by the cessation of gas accretion onto the central star. Evidence is now seen for a statistical decline in emission levels of optically-thick disks, suggesting progressive settling and/or dust growth on timescales of millions of years. There is no single timescale for disk evolution; some disks can "clear" on timescales of a million years, while roughly 10% of low-mass star disks last for up to 10 Myr. Environment may play a modest role in setting disk frequencies, even in star clusters, except for those systems very close to massive stars. Disk frequencies plunge to very low values at a given age for central star masses above one solar mass; the reason for this is unknown.Last modified: Sun Jul 9 17:40:18 2006