Research: Hydrodynamical simulations of substellar objects
Since the 1995 discovery of the first Brown Dwarf and the first Extrasolar Giant Planet , hundreds of these Substellar Objects have been detected. Despite the different formation processes of these two types of substellar objects, they have the same physics, chemistry and composition, and can therefore be described by the same models. With a mass smaller than 0.075 times the solar mass, those objects are unable to sustain thermonuclear reactions in their cores. As a result, their surface temperatures are below 2000K. The aim of this work is to simulate the observed spectra of substellar objects. To do so we need first to understand and model the atmosphere of such objects and second to simulate what happens to the radiation as it travels through this atmosphere. The atmospheres of substellar objects are cool and therefore fully convective. And convection, which is the dominant energy transport mechanism, plays also a key role in the thermal structure and chemical mixing of these atmospheres. A lot of progress has recently been made in 1D hydrostatic time-independent atmospheric models. Nevertheless, those simulations cannot take into account the dust settling or the convective overshooting. To treat the effects of convection properly, 3D hydrodynamical simulations are required. In the first part of this work we will use the FLASH code in order to simulate convection in the atmosphere of substellar objects. For this simulations an equation of state that handles low temperatures will be coupled to flash. Once the chemical and thermal structures of the atmosphere have been simulated we will perform radiative transfer simulations using this structure as an input. For this purpose we will use the PHOENIX code, which is a general tool to model the spectra of nearly all types of stellar and planetary objects. It provides modules for the equation of state, the opacities of atoms and molecules and for solving the radiative transfer equation in different geometries. Finally the spectra obtained should be compared with available observations.