IAU Symposium No. 210, Modelling of Stellar Atmospheres, 17 - 21 June 2002, Uppsala, Sweden

Proceedings: Modelling of Stellar Atmospheres, IAU Symposium, Vol. 210, 2003, N. E. Piskunov, W. W. Weiss, D. F. Gray, eds.

Sven Wedemeyer (Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany),
Bernd Freytag (Department for Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden),
Matthias Steffen (Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany),
Hans-Günter Ludwig ( Lund Observatory, Box 43, 22100 Lund, Sweden),
Hartmut Holweger (Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany),

Acoustic waves in the solar chromosphere - Numerical simulations with CO5BOLD.


It is generally assumed that the motions at the top of the solar convection zone generate acoustic waves which propagate upward into higher layers. Dissipation of these acoustic waves at chromospheric heights might provide a sufficient amount of energy to account for the observed chromospheric radiative emission.
Our aim is to check this heating mechanism with detailed numerical simulations. With CO5BOLD, a radiation hydrodynamics code developed by B.~Freytag and M.~Steffen, we are able to compute 2-D and 3-D models which include the upper convection zone, the photosphere, and the chromosphere, thus describing the generation, propagation, and dissipation of acoustic waves in a self-consistent way in the same model.
Preliminary 3-D simulations reveal complex and highly dynamic structures at chromospheric heights which are due to interaction of shock waves. Thus, the chromosphere appears as a network of hot matter. Enclosed are regions where the temperature remains low for a considerable fraction of the time. This thermal bifurcation is a prominent feature in our simulations whose observational implications for CO lines and the UV continuum have still to be worked out.


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