Convection in M-type dwarfs: predictions from 3D hydrodynamical model atmospheres

We present the first results from 3D hydrodynamical M-dwarf atmosphere simulations with the CO5BOLD model atmosphere code covering a range in Teff, log g and [M/H] typical to M0-M5 spectral type dwarfs. We provide a brief overview of the physical properties of the model atmospheres, with a focus on the validity of mixing length approximation for treating convection in the atmospheres of M-type dwarfs. We show that the mean entropy stratification can be matched only partially by changing the mixing length parameter in the 1D model atmospheres. Generally, good agreement between the 3D and 1D temperature profiles is found to approximately log tau Ross = -2 where convection stops in the 1D models. Importantly, there is no convective overshoot in the 1D models by definition whereas in case of 3D models extra convective overshoot leads to lower temperatures in the outer atmospheric layers. We discuss this and other implications that point to the necessity of using 3D hydrodynamical model atmospheres in the studies of M-type dwarfs.