Response of optical hydrogen lines to beam heating: I. Electron beams

TL;DR

This study models how non-thermal electron beams influence optical hydrogen line formation during solar flares, revealing rapid, subsecond responses that could serve as diagnostics for non-thermal electrons in the chromosphere.

Contribution

It introduces a combined radiative hydrodynamic and test-particle modeling approach to analyze hydrogen line responses to electron beam heating in flaring atmospheres.

Findings

Hydrogen lines respond within a subsecond to beam flux changes.

Line centers and wings show significant intensity variations depending on beam parameters.

Non-thermal collisional rates increase emission from secondary chromospheric regions.

Abstract

We investigate the role of non-thermal electrons in the formation regions of Halpha, Hbeta, and Hgamma lines in order to unfold their influence on the formation of these lines. We concentrate on pulse-beam heating varying on a subsecond timescale. Furthermore, we theoretically explore possibility that a new diagnostic tool exists indicating the presence of non-thermal electrons in the flaring chromosphere based on observations of optical hydrogen lines. To model the evolution of the flaring atmosphere and the time-dependent hydrogen excitation and ionisation, we used a 1-D radiative hydrodynamic code combined with a test-particle code that simulates the propagation, scattering, and thermalisation of a power-law electron beam in order to obtain the flare heating and the non-thermal collisional rates due to the interaction of the beam with the hydrogen atoms. All calculated models have shown a time-correlated response of the modelled Balmer line intensities on a subsecond timescale, with a subsecond timelag behind the beam flux. Depending on the beam parameters, both line centres and wings can show pronounced intensity variations. The non-thermal collisional rates generally result in an increased emission from a secondary region formed in the chromosphere.