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Model Atmospheres and Spectra: The Role of Dust

Published online by Cambridge University Press:  26 May 2016

France Allard ,
Tristan Guillot ,
Hans-Günter Ludwig ,
Peter H Hauschildt ,
Andreas Schweitzer ,
David R. Alexander  and
Jason W. Ferguson
France Allard
Affiliation:
CRAL-ENS, 46 Allée d'Italie, 69364 Lyon Cedex 07, France
Tristan Guillot
Affiliation:
Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 04, France
Hans-Günter Ludwig
Affiliation:
Lund Observatory, Box 43, 22100 Lund, Sweden
Peter H Hauschildt
Affiliation:
Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
Andreas Schweitzer
Affiliation:
Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
David R. Alexander
Affiliation:
Dept. of Physics, Wichita State University, Wichita, KS 67260–0032, USA
Jason W. Ferguson
Affiliation:
Dept. of Physics, Wichita State University, Wichita, KS 67260–0032, USA

Abstract

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Brown dwarf atmospheres form molecules, then high temperature condensates (corundum, titanates, silicates, and iron compounds), and then low temperature condensates (ices) as they cool down over time. These produce large opacities which govern entirely their spectral energy distribution. Just as it is important to know molecular opacities (TiO, H2O, CH4, etc.) with accuracy, it is imperative to understand the interplay of processes (e.g. condensation, sedimentation, coagulation, convection) that determines the radial and size distribution of grains. Limiting case models have shown that young, hot brown (L) dwarfs form dust mostly in equilibrium, while at much cooler stages (late T dwarfs) all high temperature condensates have sedimented out of their photospheres. But this process is gradual and all intermediate classes of brown dwarfs can partly be understood in terms of partial sedimentation of dust. With new models accounting for these processes, we describe the effects they may have upon brown dwarf spectral properties.

Type
Part 7. Atmospheres and Internal Structure
Information
Symposium - International Astronomical Union , Volume 211: Brown Dwarfs , 2003 , pp. 325 - 332
Copyright
Copyright © Astronomical Society of the Pacific 2001 

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