# The Response of the Lyman-Alpha Line in Different Flare Heating Models

## TL;DR

This study uses radiative hydrodynamic simulations to analyze how the solar Lyα line responds to different flare heating models, revealing asymmetries and intensity variations linked to chromospheric dynamics.

## Contribution

It provides the first detailed simulation-based analysis of Lyα line response considering non-equilibrium ionization and partial frequency redistribution in flare models.

## Key findings

- Non-thermal heating causes red or blue asymmetry in Lyα, indicating chromospheric evaporation or condensation.
- Asymmetry can switch from red to blue with increased electron beam flux.
- Thermal models produce a quick peak and red asymmetry in Lyα intensity.

## Abstract

The solar Ly$\alpha$ line is the strongest line in the ultraviolet waveband, and is greatly enhanced during solar flares. Here we present radiative hydrodynamic simulations of solar flares under different heating models, and calculate the response of this line taking into account non-equilibrium ionization of hydrogen and partial frequency redistribution. We find that in non-thermal heating models, the Ly$\alpha$ line can show a red or blue asymmetry corresponding to the chromospheric evaporation or condensation, respectively. The asymmetry may change from red to blue if the electron beam flux is large enough to produce a significant chromospheric condensation region. In the Ly$\alpha$ intensity lightcurve, there appears a dip when the change of asymmetry occurs. In thermal models, the Ly$\alpha$ line intensity peaks quickly and then falls, and the profile has an overall red asymmetry, which is similar to the profiles from heating by a soft electron beam. The Ly$\alpha$ profile shows a single red peak at the end of thermal heating, and the whole line is formed in a very small height range.