Multi-level non-local thermodynamic equilibrium (NLTE) radiation transfer
calculations have become standard throughout the stellar atmospheres community
and are applied to all types of stars as well as dynamical systems such as
novae and supernovae. Even today spherically symmetric 1D calculations with
full physics are computationally intensive. We show that full NLTE calculations
can be done with fully 3 dimensional (3D) radiative transfer. With modern
computational techniques and current massive parallel computational resources,
full detailed solution of the multi-level NLTE problem coupled to the solution
of the radiative transfer scattering problem can be solved without sacrificing
the micro physics description. We extend the use of a rate operator developed
to solve the coupled NLTE problem in spherically symmetric 1D systems. In order
to spread memory among processors we have implemented the NLTE/3D module with a
hierarchical domain decomposition method that distributes the NLTE levels,
radiative rates, and rate operator data over a group of processes so that each
process only holds the data for a fraction of the voxels. Each process in a
group holds all the relevant data to participate in the solution of the 3DRT
problem so that the 3DRT solution is parallelized within a domain decomposition
group. We solve a spherically symmetric system in 3D spherical coordinates in
order to directly compare our well-tested 1D code to the 3D case. We compare
three levels of tests: a) a simple H+He test calculation, b) H+He+CNO+Mg, c)
H+He+Fe. The last test is computationally large and shows that realistic
astrophysical problems are solvable now, but they do require significant
computational resources. With presently available computational resources it is
possible to solve the full 3D multi-level problem with the same detailed
micro-physics as included in 1D modeling.Comment: 20 pages, 14 figures, A&A, in pres
