H${\alpha}$ and H${\beta}$ emission in a C3.3 solar flare: comparison between observations and simulations

TL;DR

This study analyzes simultaneous high-resolution observations of a C3.3 solar flare in Hα and Hβ lines, comparing them with RADYN simulations to understand electron beam energy input and chromospheric response.

Contribution

It provides the first detailed comparison between observed Hα and Hβ emissions during a solar flare and RADYN simulation predictions, enhancing diagnostics of flare energetics.

Findings

Hα/Hβ intensity ratios are consistent with RADYN simulations for different footpoints.

Observed Hα profiles show less central reversal than models predict, suggesting partial filling factors.

Correlation between Hα and Hβ intensity excesses indicates linked chromospheric processes.

Abstract

The Hydrogen Balmer series is a basic radiative loss channel from the flaring solar chromosphere. We report here on the analysis of an extremely rare set of simultaneous observations of a solar flare in the H${\alpha}$ and H${\beta}$ lines at high spatial and temporal resolution, which were acquired at the Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22) made at various wavelengths along the H${\alpha}$ line profile by the Interferometric Bidimensional Spectrometer (IBIS) and in the H${\beta}$ with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband imager are analyzed to obtain the intensity evolution. The H${\alpha}$ and H${\beta}$ intensity excesses in three identified flare footpoints are well correlated in time. We examine the ratio of H${\alpha}$ to H${\beta}$ flare excess, which was proposed by previous authors as a possible diagnostic of the level of electron beam energy input. In the stronger footpoints, the typical value of the the H${\alpha}$/H${\beta}$ intensity ratio observed is $\sim 0.4-0.5$, in broad agreement with values obtained from a RADYN non-LTE simulation driven by an electron beam with parameters constrained (as far as possible) by observation. The weaker footpoint has a larger H${\alpha}$/H${\beta}$ ratio, again consistent with a RADYN simulation but with a smaller energy flux. The H${\alpha}$ line profiles observed have a less prominent central reversal than is predicted by the RADYN results, but can be brought into agreement if the H${\alpha}$-emitting material has a filling factor of around 0.2--0.3.