Other
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001ense.conf...45h&link_type=abstract
Proceeding to the 4th Prague Seminar: Euler & Navier-Stokes Equations - Theory, Numerical Solutions, Apllications; eds. Kozel, P
Other
Dust Formation, Stellar Atmospheres, Brown Dwarfs
Scientific paper
Brown Dwarfs are very faint, low mass star-like objects possibly bridging the gap between stars and planets. Their interior is dominated by convective energy transport which deposits energy, momentum, and matter into the atmosphere. Brown Dwarf atmospheres furthermore provide favorable conditions for the gas--solid phase transition due to their low temperatures and high densities since they are cool and compact objects. Brown Dwarfs are therefore an excellent test bed to study dust formation under turbulent conditions. In Brown Dwarfs, dust-free convective cells originating from the interior convective zone travel radially outward and decay into smaller and smaller eddies. Following Kolmogoroff's assumption, energy is transfered from the largest scales into smaller and smaller scales until the energy is finally dissipated on the Kolmogoroff scale (η ≈ 10-2cm for lref≈104cm) by the viscosity of the gas. Considering that the large scale turbulent motions have a characteristic Mach number M≈ 1, resulting acoustic waves create a turbulent temperature and density field in the atmosphere which influences the dust complex due to its high temperature and density sensitivity. Combining asymptotic techniques and time-dependent, multi-dimensional numerical simulations, we show that on microscopic scales acoustic waves can initiate dust nucleation in otherwise dust-hostile environments. An instable feedback loop occurs which is started by small temperature disturbances which allow the first dust particles to form. These particles grow to macroscopic sizes and thereby intensify the temperature decrease due to the radiative cooling which in turn re-initiates and henceforth intensifies dust formation. This runaway effect is stopped if all condensible material is consumed or the radiative equilibrium is reached.
Helling Ch.
Klein Ralf
Lüttke M.
Oevermann M.
Sedlmayr Erwin
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