Repository: Freie Universit├Ąt Berlin, Math Department

Dust in brown dwarfs. IV. Dust formation and driven turbulence on mesoscopic scales

Helling, Ch. and Klein, R. and Woitke, P. and Nowak, U. and Sedlmayr, E. (2004) Dust in brown dwarfs. IV. Dust formation and driven turbulence on mesoscopic scales. Astronomy and astrophysics, 423 (2). pp. 657-675. ISSN 0004-6361

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Abstract

Dust formation in brown dwarf atmospheres is studied by utilising a model for driven turbulence in the mesoscopic scale regime. We apply a pseudo-spectral method where waves are created and superimposed within a limited wavenumber interval. The turbulent kinetic energy distribution follows the Kolmogoroff spectrum which is assumed to be the most likely value. Such superimposed, stochastic waves may occur in a convectively active environment. They cause nucleation fronts and nucleation events and thereby initiate the dust formation process which continues until all condensible material is consumed. Small disturbances are found to have a large impact on the dust forming system. An initially dust-hostile region, which may originally be optically thin, becomes optically thick in a patchy-way showing considerable variations in the dust properties during the formation process. The dust appears in lanes and curls as a result of the interaction with waves, i.e. turbulence, which form larger and larger structures with time. Aiming at a physical understanding of the variability of brown dwarfs, related to structure formation in substellar atmospheres, we work out first necessary criteria for small-scale closure models to be applied in macroscopic simulations of dust-forming astrophysical systems.

Item Type:Article
Uncontrolled Keywords:Low-mass stars ; Dust lane ; Disturbances ; Nucleation ; Kinetic energy ; Spectral method ; Closure model ; Mesoscopic systems ; Turbulence ; Brown dwarf stars ;
Subjects:Mathematical and Computer Sciences > Mathematics > Applied Mathematics
Divisions:Department of Mathematics and Computer Science > Institute of Mathematics > Geophysical Fluid Dynamics Group
ID Code:535
Deposited By: Ulrike Eickers
Deposited On:13 Jul 2009 12:33
Last Modified:13 Jul 2009 12:33

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