Full non-LTE spectral line formation I. Setting the stage

TL;DR

This paper introduces the full non-LTE spectral line formation problem, emphasizing the importance of self-consistently solving for deviations in both photon and particle distributions in astrophysical atmospheres.

Contribution

It revisits the full non-LTE problem, extending beyond standard approaches by coupling photon and particle distribution deviations self-consistently.

Findings

Highlights the need for self-consistent solutions in non-LTE modeling

Revisits and builds upon Oxenius (1986) framework

Sets the stage for more comprehensive spectral line formation analysis

Abstract

Radiative transfer out of local thermodynamic equilibrium (LTE) has been increasingly adressed, mostly numerically, for about six decades now. However the standard non-LTE problem most often refers to the only deviation of the distribution of photons from their equilibrium i.e., Planckian, distribution. Hereafter we revisit after Oxenius (1986) the so-called "full non-LTE" problem, which considers to couple and therefore to solve self-consistently for deviations from equilibrium distributions of photons as well as for massive particles constituting the atmospheric plasma.