We present results from 2D radiation-hydrodynamical simulations of fully
compressible convection for the surface layers of A-type stars with the ANTARES
code. Spectroscopic indicators for photospheric convective velocity fields show
a maximum of velocities near Teff ~8000 K. In that range the largest values are
measured for the subgroup of Am stars. Thus far, no prognostic model, neither
theoretical nor numerical, is able to exactly reproduce the line profiles of
sharp line A and Am stars in that temperature range. In general, the helium
abundance of A stars is not known from observations. Hence, we have considered
two extreme cases for our simulations: a solar helium abundance as an upper
limit and zero helium abundance as a lower limit. The simulation for the helium
free case is found to differ from the case with solar helium abundance by
larger velocities, larger flow structures, and by a sign reversal of the flux
of kinetic energy inside the hydrogen ionisation zone. Both simulations show
extended shock fronts emerging from the optical surface, as well as mixing far
below the region of partial ionisation of hydrogen, and vertical oscillations
emerging after initial perturbations have been damped. We discuss problems
related to the rapid radiative cooling at the surface of A-type stars such as
resolution and efficient relaxation. The present work is considered as a step
towards a systematic study of convection in A- to F-type stars, encouraged by
the new data becoming available for these objects from both asteroseismological
missions and from high resolution spectroscopy.Comment: submitted to CoAst, preprint version with 26 pages (29 pages in CoAst
layout), 8 figures, 1 tabl
