Bibcode
Asensio Ramos, A.; Trujillo Bueno, J.
Referencia bibliográfica
EAS Publications Series, Volume 18, 2006, pp.25-48
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2006
Número de citas
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Descripción
The development of fast numerical methods for multilevel radiative
transfer (RT) applications often leads to important breakthroughs in
astrophysics, because they allow the investigation of problems that
could not be properly tackled using the methods previously available.
Probably, the most familiar example is the so-called Multilevel
Accelerated Λ-Iteration (MALI) technique of Rybicki & Hummer
for the case of a local approximate operator, which is based on Jacobi
iteration. However, there are superior operator-splitting methods, based
on Gauss-Seidel (GS) and Successive Overrelaxation (SOR) iteration,
which provide a dramatic increase in the speed with which non-LTE
multilevel transfer problems can be solved in one, two and
three-dimensional geometries. Such RT methods, which were introduced by
Trujillo Bueno & Fabiani Bendicho ten years ago, are the main
subject of the first part of this paper. We show in some detail how they
can be applied for solving multilevel RT problems in spherical geometry,
for both atomic and molecular line transitions. The second part of the
article addresses the issue of the calculation of the molecular number
densities when the approximation of instantaneous chemical equilibrium
turns out to be inadequate, which happens to be the case whenever the
dynamical time scales of the astrophysical plasma under consideration
are much shorter than the time needed by the molecules to form.