After years of work on 2-dimensional (2D) simulations of convection in
the surface layers of stars as diverse as white dwarfs and red giants,
Bernd Freytag
(now University of Uppsala, Sweden) and
Matthias Steffen
(Stellar Physics, AIP) have developed a completely new radiation hydrodynamics
code suitable for fully 3-dimensional (3D) simulations of stellar convection.
This code was subjected to a critical test in November 2000, when it
was applied to a first simulation of the solar granulation,
using 140x140x120 gird points and 176400 rays for the calculation
of the radiation field (LTE, grey). Rotation and magnetic fields
are ignored. Computations were carried out on an XP1000 workstation at
the AIP.
The images above show the emergent intensity (at 6200 A), corresponding
to a view from above the solar surface. Starting from a 2D initial
configuration (left), the flow quickly develops a 3D structure, the high
wavenumber modes showing the largest growth rates (middle). Finally,
the ever changing, typical granulation pattern emerges (right), leaving
no hint of the initial model.
A detailed comparison with
modern high-resolution observations of the solar granulation by Krieg et al.
(2000, A&A, 360, 1157)
will allow an assessment the realism of the new models.
In the future, we plan to employ simulations of this kind to validate the
results obtained so far from 2D models, to study the generation of acoustic
energy by turbulent convection and the (non-magnetic) heating
of the solar chromosphere, and to obtain quantitative estimates of the
effects of photospheric temperature inhomogeneities on spectroscopic abundance
determinations, particularly in very metal-poor solar-type stars.
( credit: M. Steffen, AIP ).
