Full non-LTE spectral line formation II. Two-distribution radiation transfer with coherent scattering in the atom's frame

TL;DR

This paper introduces a numerical method for solving full non-LTE radiation transfer problems, incorporating two-distribution radiation transfer with coherent scattering, and demonstrates its application with benchmark tests and new physical insights.

Contribution

It develops a novel numerical approach for full non-LTE radiation transfer using a two-distribution formalism, extending previous methods and enabling access to new physical quantities.

Findings

Validated with standard two-level atom tests

Produced new spatial velocity distribution profiles

Enhanced understanding of non-LTE radiation processes

Abstract

In the present article, we discuss a numerical method of solution for the so-called "full non-LTE" radiation transfer problem, basic formalism of which was revisited by Paletou & Peymirat (2021; see also Oxenius 1986). More specifically, usual numerical iterative methods for non-LTE radiation transfer are coupled with the above-mentioned formalism. New numerical additions are explained in detail. We benchmark the whole process with the standard non-LTE transfer problem for a two-level atom with Hummer's (1962, 1969) $R_{\rm I-A}$ partial frequency redistribution function. We finally display new quantities such as the spatial distribution of the velocity distribution function of excited atoms, that can only be accessed to by adopting this more general frame for non-LTE radiation transfer.