Accurate Radiation Hydrodynamics and MHD Modeling of 3-D Stellar Atmospheres

Abstract

Stellar atmospheres provide a unique and valuable testing ground for radiation hydrodynamics and MHD. Spectral line synthesis based on reasonably affordable 3‐D models can potentially reach very high accuracy, with widths, strengths, and shapes of photospheric spectral lines matching observations to within fractions of a percent, with “no free parameters”; i.e., using only the effective temperature, surface acceleration of gravity, and element abundances as input parameters, and without the need for artificial fitting parameters such as micro‐ and macro‐turbulence. When combined with accurate atomic parameters the results can be used to determine the abundance of individual chemical elements more accurately than was possible in the past, when spectral line synthesis was based on one‐dimensional modeling and artificial fitting parameters. A necessary condition for reaching the desired accuracy is that the radiative energy transfer in the photosphere is treated with sufficient accuracy. Since at different l...