Numerical Simulations of Stellar Surface Convection and Related Phenomena

CRAL-ENS Lyon, France

Abstract

Sophisticated radiative transfer methods have been used for decades to model one-dimensional static stellar atmospheres. They predict an outward decrease of the atmospheric temperature that is now observable with simple one-baseline interferometers via measurements of limb darkening. However, the surface layers of many stars are affected by convection which requires a treatment by time-dependent multi-dimensional radiation hydrodynamics simulations. Solar granulation is directly observable with “ordinary” telescopes. The simulated granule pattern and evolution compares well with the observed ones. The upcoming radio interferometer ALMA could be used to probe the convection induced shock-pattern in the chromosphere that is predicted by simulations and that is not easily observable otherwise. The typical granular scale on other near main-sequence stars is too small to be accessible by interferometers. However, scaling arguments and recent numerical simulations predict very large structures on cool supergiants and AGB stars. These stars were and are candidates for optical/near-infrared interferometry. The complexity of the predicted surface phenomena requires good (or at least some) spatial resolution in conjunction with temporal and frequency resolution. To fully exploit and interpret these data the simulations have to be improved in terms of treatment of microphysics (especially opacities in the radiative transfer step) and spatial resolution.