Most stars show strong magnetic fields on their surfaces and sustain a hot outer atmosphere, the corona. Two of the fundamental problems in stellar astrophysics are how the stars generate their magnetic field, and how they manage to heat the corona to temperatures of two million K, well in excess of the surface. I will address these problems by performing local and global numerical simulations. These include the stellar interior and an overlaying corona, which are evolved self-consistently by solving the magnetohydrodynamic equations using high performance computing. First results of such novel simulations show that the dynamo benefits substantially from the presence of a corona leading to a stronger amplification of the magnetic field inside the star and that the dynamo can drive dynamic events in the corona. For a more complete understanding of the coupled dynamo-corona system, further steps towards more realistic models have to be taken. The overall goal of the proposed project can be subdivided into three major parts:
(1) understand fundamental properties of stellar dynamos using accurate mean-field models of the direct numerical simulations,
(2) investigate the influence of the coronal envelope on stellar dynamos and stellar interiors,
(3) determine the role of stellar dynamos for the formation and evolution of coronal structures.
This study will have a major impact on the fundamental understanding of solar and stellar activity cycles, which is pivotal for interpretation of stellar observations. In particular this concerns the description of the solar and stellar dynamo processes, the formation of space-weather events and the coronal heating mechanisms. Modeling the exact relation between stellar parameters, dynamos in the interior and coronal properties will for the first time provide a clear interpretation of observable atmospheric quantities for a large range of stars, for example the relation of rotation rate and stellar X-ray luminosity.
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