Full non-LTE spectral line formation

II. Two-distribution radiation transfer with coherent scattering in the atom’s frame

¹ Université de Toulouse, UPS-Observatoire Midi-Pyrénées, CNRS, CNES, IRAP, 31028 Toulouse Cedex 4, France
e-mail: frederic.paletou@univ-tlse3.fr
² CNRS, Institut de Recherche en Astrophysique et Planétologie, 14 av. E. Belin, 31400 Toulouse, France
³ Indian Institute of Astrophysics, Koramangala, Bengaluru 560034, India
⁴ Université de Toulouse, Faculté des Sciences et de l’Ingénierie, 31062 Toulouse Cedex 9, France

Received: 7 September 2022
Accepted: 8 January 2023

Abstract

In this article we discuss a method for obtaining a numerical solution to the so-called full nonlocal thermodynamic equilibrium (non-LTE) radiation transfer problem. More specifically, the usual numerical iterative methods for non-LTE radiation transfer are coupled with that formalism and new numerical additions are explained in detail. We benchmarked the whole process with the standard non-LTE transfer problem for a two-level atom with Hummer’s R_I − A partial frequency redistribution function. Finally, we present new quantities, such as the spatial distribution of the velocity distribution function of excited atoms, which can only be accessed by adopting a more general frame for non-LTE radiation transfer, such as the one we propose here.