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Paper: Radiation-Hydrodynamics Simulations of Cool Stellar and Substellar Atmospheres
Volume: 448, 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
Page: 855
Authors: Freytag, B.; Allard, F.; Ludwig, H.-G.; Homeier, D.; Steffen, M.
Abstract: In the atmospheres of brown dwarfs, not only molecules but much larger and heavier “dust” particles can form. The latter should sink under the influence of gravity into deeper layers and vanish from the atmosphere, clearing it from condensable material. However, observed spectra can only be reproduced by models assuming the presence of dust and its resulting greenhouse effect in the visible layers. Apparently, hydrodynamical mixing can counteract the gravitational settling. We present new 2D and 3D radiation-hydrodynamics simulations with CO5BOLD of the upper part of the convection zone and the atmosphere of cool stars and brown dwarfs in a range of temperatures and gravities that enable the formation of dust clouds in the visible layers. We find that the differences between 2D and 3D models are remarkably small. Lowering the gravity has a somewhat similar effect on the surface intensity contrast as increasing the effective temperature. The biggest uncertainties of the simulations come from approximations made in the description of the dust chemistry. Global circulation and rotation likely play an important role.
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