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Z.E. Musielak (UTA, UAH), M. Cuntz (UAH), P. Ulmschneider (Univ. Heidelberg)
To identify the basic physical processes that underlie stellar chromospheric activity, we have taken a novel theoretical approach and constructed first purely theoretical, two-component and time-dependent models of stellar chromospheres. Our models require specifying only four basic stellar parameters, namely, the effective temperature, gravity, metallicity and rotation rate, and they take into account non-magnetic and magnetic regions in stellar chromospheres. The non-magnetic regions are heated by acoustic waves generated by the turbulent convection in the stellar subphotospheric layers. The magnetic regions are identified with magnetic flux tubes uniformly distributed over the entire stellar surface and are heated by longitudinal tube waves generated by turbulent motions in the subphotospheric and photospheric layers. The coverage of stellar surface by magnetic regions (the so-called filling factor) is estimated for a given rotation rate from an observational relationship. The constructed models are based on the energy balance between the amount of mechanical energy supplied by waves and radiative losses in strong Ca II and Mg II emission lines. We have already used our chromospheric models to predict the level of ``basal flux'' and the decrease of chromospheric activity with stellar rotation in selected late-type dwarfs. We present these new results and discuss how to include stellar transition regions, coronae and winds in our models.
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The author(s) of this abstract have provided an email address for comments about the abstract: musielakz@utahep.uta.edu