David HOLLENBACH : NASA Ames Research Center
Disc Dispersal Mechanisms
We briefly review the evidence pertaining to the lifetimes of planet-forming disks of gas and dust around young stars and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, 4) photoevaporation caused by the heating of the disk surface by ultraviolet radiation, and 5) planet formation. Viscous accretion likely dominates in the inner regions of disks, while photoevaporation is likely the most important dispersal mechanism for the outer regions. This review focuses on photoevaporation caused by the presence of a nearby, UV-luminous star as well as by the central star itself. We discuss the effects of both the EUV (hydrogen-ionizing) and FUV fluxes, with emphasis on new results on the photoevaporation by FUV fluxes from the central star and the dependence of photoevaporation lifetimes on the central stellar mass. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter or gas-poor giants like Neptune around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We propose to use infrared spectroscopy to constrain and validate photoevaporation models.Last modified: Sun Jul 9 17:41:49 2006