Radiation Hydrodynamics Simulations of Dust Clouds in the Atmospheres of Substellar Objects

摘要

The temperature structure and the motions in the atmospheres of cool stars are affected by the underlying convection zone. The radiation hydrodynamics code CO5BOLD has been developed to simulate (small patches of the) convective surface layers of these stars. Updated opacity tables based on PHOENIX data and a description for the formation, destruction, advective transport, and settling of dust have made the code fit to handle the conditions in brown dwarf atmospheres. Currently, objects from 8500 K down to about 900 K have been simulated. Recently, incident radiation has been included, allowing simulations with conditions found on hot planets. In non-irradiated brown dwarf models we encounter mixing by gravity waves and in the cooler models convection within the clouds. The qualitative effects of incident radiation are surprisingly small, as long as the effective temperature of the object stays well below the dust condensation temperature. Beyond that point, there are no layers where dust could form, anymore.