Towards simulating convection in substellar objects

Abstract

Convection is the main energy transport mechanism in the interior of substellar objects and therefore plays a crucial role in its resulting structure. Most of the existing models use the mixing length theory approximation to account for the effects of convection. Nevertheless, this approximation is inadequate when considering certain convective effects, and it is therefore relevant to simulate convection explicitly. Due to the low temperatures encountered in substellar objects, chemical phenomena such as molecule formation, have to be considered. To do so, we couple a state of the art equation of state (ACES-EOS) to the FLASH code. This ACES-EOS is a module of the PHOENIX code and can be used for temperatures as low as 100K. We present the results of a test case, where we simulate an object with 2800 K effective temperature and log(g)=5. In this M-dwarf test simulation using the “FLASH+ACES-EOS” code, we found granule-like structures with warmer and less dense regions moving upwards and colder denser regions moving downwards. The “FLASH+ACES-EOS” temperature, density and pressure altitude-mean-profiles are in very good agreement with PHOENIX/1D models and the rms z-velocity values of around 0.2km/s are similar to those obtained by previous studies.