Radiative transfer in cylindrical threads with incident radiation VII. Multi-thread models

TL;DR

This paper presents a novel two-dimensional multi-thread radiative transfer model for cylindrical solar atmospheric structures, enabling detailed synthetic spectra computation and analysis of multi-thread effects on observed emissions.

Contribution

It introduces the first multi-thread 2D radiative transfer models combining hydrogen and helium for cylindrical solar structures, advancing the interpretation of high-resolution solar observations.

Findings

Multi-thread models significantly affect emergent spectra.

Line-of-sight velocities influence spectral line profiles.

Temperature and pressure variations alter radiative transfer outcomes.

Abstract

We solved the radiative transfer and statistical equilibrium equations in a two-dimensional cross-section of a cylindrical structure oriented horizontally and lying above the solar surface. The cylinder is filled with a mixture of hydrogen and helium and is illuminated at a given altitude from the solar disc. We constructed simple models made from a single thread or from an ensemble of several threads along the line of sight. This first use of two-dimensional, multi-thread fine structure modelling combining hydrogen and helium radiative transfer allowed us to compute synthetic emergent spectra from cylindrical structures and to study the effect of line-of-sight integration of an ensemble of threads under a range of physical conditions. We analysed the effects of variations in temperature distribution and in gas pressure. We considered the effect of multi-thread structures within a given field of view and the effect of peculiar velocities between the structures in a multi-thread model. We compared these new models to the single thread model and tested them with varying parameters. These new computations show, for the first time, the effect of integrating the radiation emitted in H and He lines by several cylindrical threads that are static or moving along the line of sight. They can be used to interpret high-spatial and spectral resolutions of cylindrical structures found in the solar atmosphere, such as cool coronal loops or prominence threads.