Diagnostics for the solar chromosphere using neutral carbon Rydberg lines

TL;DR

This paper explores the diagnostic potential of neutral carbon Rydberg lines in the solar chromosphere by modeling their formation and response to atmospheric changes, paving the way for improved atmospheric reconstructions.

Contribution

It demonstrates the use of recent atomic data and radiative transfer modeling to assess the diagnostic utility of neutral carbon Rydberg lines in the solar chromosphere.

Findings

Lines are sensitive to temperature, density, and micro-turbulence.

Optical depth effects influence line formation.

Potential for atmospheric inversion using these lines.

Abstract

Diagnostics for the solar chromosphere are relatively few compared to other parts of the atmosphere. Despite this, hundreds of Rydberg lines emitted by neutrals in this region have been observed at UV wavelengths. Here, we investigate their diagnostic potential by modelling the lines emitted by neutral carbon using recent atomic data. We use the radiative transfer code Lightweaver to explore how they form and how they respond to temperature, density and micro-turbulent velocity perturbations in the atmosphere. To simplify the modelling, we investigate lines emitted from levels with principal quantum number $n\geq10$, which are expected to be in Saha-Boltzmann equilibrium with the ground state of the singly-charged ion. Optical depth effects are apparent in the lines and their response to atmospheric perturbations suggest that they will be useful in reconstructions of the atmosphere using inversions. The study opens the way for using many such lines emitted by multiple elements over a range of heights, a large number of which will be observed by the forthcoming Solar-C EUV High-throughput Spectroscopic Telescope (EUVST).