We have carried out detailed numerical simulations of solar granular convection cells of different horizontal dimension. The calculations account for the basic physics of compressible convection, including the ionization of H I, He I and He II, and H2 molecule formation as well as non-local, multi-dimensional radiative transfer (grey approximation in LTE). A more detailed description of the simulations has been given by Steffen and Muchmore (1988) and by Steffen et al. (1989).

A non-LTE abundance determination of magnesium, iron, and barium was carried out for the atmosphere of Vega. The results indicate marked underabundances of these elements relative to the solar values. First preliminary results of numerical simulations of convective and oscillatory phenomena in the atmosphere of Vega are briefly described.