Abstract

Model Atmospheres of Stars, Brown Dwarfs, and Planetary Mass Objects

France Allard (CRAL-ENS)

The spectral transition from Very Low Mass stars (VLMs) to brown dwarfs (BDs) and planetary mass objects (Planemos) requires model atmospheres that can treat with completeness and accuracy line, molecule and dust-cloud formation. One of the essential problems is the determination of the surface velocity field throughout the main sequence down to the BD and planemo mass regimes. We present local radiation hydrodynamic simulations using CO5BOLD (B. Freytag) based on Phoenix’s gas opacities, which account for forsterite formation (2 and 3D) and rotation (3D). The resulting velocity field vs depth and Teff (Freytag et al. 2010) has been used in the general atmosphere code PHOENIX, adapted in static 1D spherical symmetry for the case of VLMs, BDs, and planemos by Allard et al. (1995, 1997, 2001, 2007). The result is a better explanation of the spectral transition from the stellar to the BDs and plenamos regimes. However, clearly, the global properties of rotation can change the averaged properties of these objects. Our project for the period 2011-2015 is therefore to develop global 3D simulations of convection, cloud formation and rotation for these objects, thanks to funding by the Agence Nationale de la Recherche in France.