Continued progress in observational stellar astrophysics requires a deep
understanding of the underlying convection dynamics. We present results of
realistic 3D radiative hydrodynamic simulations of the outer layers of a
moderate mass star (1.47 Msun), including the full convection zone, the
overshoot region, and the top layers of the radiative zone. The simulation
results show that the surface granulation has a broad range of scales, from 2
to 12 Mm, and that large granules are organized in well-defined clusters,
consisting of several granules. Comparison of the mean structure profiles from
3D simulations with the corresponding 1D standard stellar model shows an
increase of the stellar radius by ~800 km, as well as significant changes in
the thermodynamic structure and turbulent properties of the ionization zones.
Convective downdrafts in the intergranular lanes between granulation clusters
reach speeds of more than 20 km/s, penetrate through the whole convection zone,
hit the radiative zone, and form a 8 Mm thick overshoot layer. Contrary to
semi-empirical overshooting models, our results show that the 3D dynamic
overshoot region consists of two layers: a nearly adiabatic extension of the
convection zone and a deeper layer of enhanced subadiabatic stratification.
This layer is formed because of heating caused by the braking of the
overshooting convective plumes. This effect has to be taken into account in
stellar modeling and the interpretation of asteroseismology data. In
particular, we demonstrate that the 3D model can qualitatively explain
deviations from the standard solar model found by helioseismology.Comment: 14 pages, 5 figures, submitted to ApJ Letter
