Hydrodynamic Photoevaporation of Protoplanetary Disks with Consistent Thermochemistry

Abstract

Photoevaporation is an important dispersal mechanism for protoplanetary disks. We conduct hydrodynamic simulations coupled with ray-tracing radiative transfer and consistent thermochemistry to study photoevaporative winds driven by ultraviolet and X-ray radiation from the host star. Most models have a three-layer structure: a cold midplane, warm intermediate layer, and hot wind, the last having typical speeds similar to 40 km s(-1) and mass-loss rates similar to 10(-9) M-circle dot yr(-1) when driven primarily by ionizing UV radiation. Observable molecules, including CO, OH, and H2O re-form in the intermediate layer and survive at relatively high wind temperatures due to reactions being out of equilibrium. Mass-loss rates are sensitive to the intensity of radiation in energy bands that interact directly with hydrogen. Comparison with previous works shows that mass-loss rates are also sensitive to the treatment of both the hydrodynamics and thermochemistry. Divergent results concerning the efficiency of X-ray photoevaporation are traced in part to differing assumptions about dust and other coolants.