Photoevaporation of protostellar disks II. The importance of UV dust properties and ionizing flux

We study the hydrodynamic evolution of protostellar disks under the influence of a central source of ionizing radiation and its stellar wind. Here we examine the effects of an important contribution to the diffuse radiation field – the scattering of hydrogen-ionizing photons on dust grains (dust scattering). We present and discuss the resulting changes in the evolution of the system under a variety of conditions both with and without dust scattering. An important consequence is the significant increase in the photoevaporation rate. Depending on the scattering coefficient assumed, the presence of dust within the ionized region can increase the density and flow of ionized material and correspondingly shorten the disk’s lifetime by a factor of two or more. In addition, the temperature of the ionized outflowing gas is slightly higher and remains more nearly constant over the extent of the ionized region, even in the regions shadowed from direct stellar radiation. We also investigate the influence of other major parameters of the problem, wind velocity, wind mass loss rate, and stellar ionizing flux, by systematically varying these parameters. Over a large range of values of stellar ionizing flux Sstar we find a power law dependence of the disk mass loss rate due to photoionization Ṁph ∝ S0.58 star which is comparable to analytic estimates. Deviations from this power law occurred for moderate valuesSstar >∼ 1047 s−1 due to our finite disk size and for low valuesSstar <∼ 1045 s−1 due to the resulting non-steady flow pattern. Because we have assumed a warm (T ≈ 104 K) wind and have included heating, cooling, ionization, and recombination processes in the stellar wind, we find that the disk’s photoevaporation rate depends on the assumedwind parameters in amanner which can be explained by the loss of UV ionizing photons very close to the central star.