Modeling the three-dimensional structure and dynamics of the corona of the Sun and stars

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A cool star like our Sun is surrounded by an outer atmosphere, the corona, which is a hundred times hotter than its surface ¿ still being an unsolved puzzle. Among other heating processes it was suggested that the magnetic field lines in the corona are braided by motions on the stellar surface. The subsequent dissipation of the induced currents leads to efficient heating of the corona up to a million degrees. The progress in computer power now allows us to study the corona by means of three-dimensional time-dependent models of the fluid dynamics including magnetic fields. Our simulations are coupled with a synthesis of extreme ultraviolet emission line spectra, which is essential for a detailed comparison to observations. These models will be the first to account for the complex interaction of regions with strong and weak magnetic fields, allowing for an investigation of the 3D structure and dynamics of the low corona. If our preliminary results will be substantiated, we can provide ample evidence that the field line braiding indeed is the dominant heating mechanism, which would be a large step forward in understanding coronal heating. Our results will also have impact on the study of hot magnetically heated plasmas in other astrophysical objects, like accretion disks surrounding a newly formed star with its (potential) planets. Furthermore, the solar corona as being the source of the extreme ultraviolet radiation, is of interest for the chemistry of the upper Earth s atmosphere.