Poster abstract

Since the 1995 discovery of the first Brown Dwarf and the first Extrasolar Giant Planet, hundreds of these Sub-stellar Objects (SSO) have been detected. With surface temperatures below 2000K, convection is the dominant energy transport mechanism and plays a key role in the thermal structure and chemical mixing of their atmospheres. Modeling such cool atmospheres has proven to be challenging. An enormous progress has been made in the treatment of opacities and in the development of an Equation of State (EOS), but the mixing length theory (MLT) is still widely used as an approximation for convection.
We treat convection in a more realistic way. We use the FLASH Code to perform 3D hydrodynamical simulations in order to study the various effects of convection in the SSO atmospheres. Since molecules form at such low temperatures and these chemical processes can energetically play an important role for the onset of convection, the choice of the EOS is crucial. We have coupled to the FLASH code a realistic and detailed EOS, which is a module of the PHOENIX code. This EOS can handle the low temperatures encountered in the sub-stellar objects' atmospheres through a detailed treatment of the physical and chemical phenomena.
We will present the advantages and limitations of this approach, and the current status of the project.