Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling

TL;DR

This review discusses spectral diagnostics and advanced non-LTE radiative transfer models to analyze solar prominences, highlighting recent progress, challenges, and future research directions in understanding prominence plasma properties.

Contribution

It provides a comprehensive overview of non-LTE modeling techniques and their application to prominence spectral analysis, including recent advances and unresolved questions.

Findings

Spectral inversion techniques help infer plasma parameters.

Non-LTE models are essential for optically thick lines.

Energy balance in prominences remains an open question.

Abstract

This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (ie when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.