Abstract
Dwarf stars of spectral type M are the most frequent stars in the universe. And yet little is known about the properties of their atmospheres.
"M-dwarfs" are nevertheless of fundamental interest for a wide range of astrophysical topics including the chemical evolution and composition of the universe, their role as host stars of extra-solar planets, and stellar magnetism in general. Observations of chromospheric activity clearly imply the existence of magnetic fields in M-dwarf atmospheres but it is currently debated whether they are generated by a global dynamo in the interior or rather a local dynamo process at the surface. After an introduction to these cool stars, I will present first (preliminary) results of 3-D numerical simulations for M-dwarf atmospheres.
The resulting models, which reveal an intermittent and dynamic atmospheric structure, go far beyond the scope of commonly used semi-empirical 1-D models. I will discuss potential implications of this new class of models and their value for an improved interpretation of observations.