3D Non-LTE radiation transfer: theory and applications to stars, exoplanets, and kilonovae

TL;DR

This paper reviews recent advances in 3D Non-LTE radiation transfer modeling, highlighting its importance for accurately interpreting spectra from stars, exoplanets, and kilonovae, and discusses methodological developments and applications.

Contribution

It provides a comprehensive overview of 3D NLTE radiation transfer theory, recent methodological improvements, and diverse astrophysical applications, emphasizing the physical accuracy of spectral modeling.

Findings

Identification of systematic shortcomings in canonical models

Advances in multi-D transfer modeling techniques

Application to diverse astrophysical environments

Abstract

Most of the physical information about astrophysical objects is obtained via the analysis of their electromagnetic spectra. Observed data coupled with radiation transfer models in physical conditions representative of stars, planets, kilonovae, and ISM, yield constrains on their physical structure, gas flow dynamics at the surface, mass loss, and detailed chemical composition of the systems. All these core astrophysical parameters are just as reliable as the physical quality of the models that are employed for simulations of radiation transfer. Recent advances in multi-D transfer modeling with Non-Local Thermodynamic Equilibrium (NLTE) in inhomogeneous time-dependent systems revealed systematic shortcomings of canonical models. Owing to major complexities of solving coupled multi-frequency RT equations in 3D geometry, a number of approximations have been introduced. This review presents an overview of the physical problem, standard solutions, and recent methodological advances. We also provide an overview of main results in the area of 3D NLTE radiation transfer and its applications to modeling diverse astrophysical environments, including FGKM type- and OBA-type stars, multi-epoch spectra of kilonovae, and atmospheres of rocky and gaseous exoplanets.