The evaporation of spherical clouds in a hot gas. III - Suprathermal evaporation

A steady-state model is developed for the thermal evaporation of isolated spherical clouds in the limit where the collisional mean free path of the hot ambient electrons is very much larger than the characteristic length scale associated with the evaporative outflow. The process is referred to as suprathermal evaporation. The energy equation used takes in both the effects of direct Coulomb collisions between the suprathermal particles and the thermal gas of the evaporative outflow, as well as flux-limited conductive heating of the outflow. The fluid dynamical equation for the flow make possible two categories of solution: one in which conductive heating dominates near the cloud, the other in which Coulomb heating dominates. In the first type of solution, the mass loss rate is found to be an eigenvalue of the equations; in the second type, the effects of the radiative losses in the cloud interior must be considered to determine the mass loss rate.