Cool Stars 14 - Submitted Abstract # 79
This version created on 05 October 2006

The influence of non-equilibrium dust formation on the atmosphere of
brown dwarfs


Matthias Dehn, Hamburger Sternwarte, Germany
Christiane Helling, University of St Andrews, United Kingdom
Peter Woitke, Sterrewacht Leiden, The Netherlands
Peter H. Hauschildt, Hamburger Sternwarte, Germany

Available dust models often assume phase-equilibrium for dust
formation to deliver the depletion of gas phase elements which form
condensed matter.  These models are successfully used to provide
opacities in radiative transfer codes.  More detailed,
self--consistent modeling of the quasi--static dust problem using a
kinetic approach assumes equilibrium chemistry and considers
nucleation of TiO2 seed particles, a dirty growth and gravitational
drift of the particles (Woitke & Helling 2003, 2004).  Nevertheless,
the feedback on atmospheric structures could not been taken into
account until now:  The problem of coupling the dust formation and its
impact on the radiation field is iteratively being solved using the
classic stellar atmosphere code PHOENIX (Hauschild & Baron 1999) by
solving the frequency dependent radiative transfer and the structure
of the atmosphere in hydrostatic equilibrium.  The dust model by
Woitke & Helling (2003, 2004) and Helling & Woitke 2006) for
oxygen--rich dwarfs needs an atmospheric structure and provides
properties of the dust clouds, which, in turn, allows to calculate
dust opacities as input for the radiative transfer problem.  We
demonstrate recent progress of modeling late--type stars of spectral
type L having effective temperatures of 1700...2100  K.  We discuss
the change of spectral appearance and the change of 2MASS-colors J--K
with varying column density of the dust.

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