A Flare Observed in Coronal, Transition Region and Helium I 10830 \AA\ Emissions

TL;DR

This study analyzes a solar flare observed in multiple wavelengths, revealing that He I 10830 Å emission is mainly due to photoionization and recombination, supporting models of energy transfer from corona to chromosphere.

Contribution

It provides new insights into the formation of He I 10830 Å emission during flares, emphasizing the role of photoionization and recombination processes.

Findings

He I 10830 Å emission is driven by photoionization and radiative recombination.

He II 304 Å line matches standard emission measure calculations.

Supports models of energy transport from corona to chromosphere.

Abstract

On June 17, 2012, we observed the evolution of a C-class flare associated with the eruption of a filament near a large sunspot in the active region NOAA 11504. We obtained high spatial resolution filtergrams using the 1.6 m New Solar Telescope at the Big Bear Solar Observatory in broad-band TiO at 706 nm (bandpass:10 \AA) and He I 10830 \AA\ narrow-band (bandpass: 0.5 \AA, centered 0.25 \AA\ to the blue). We analyze the spatio-temporal behavior of the He I 10830 \AA\ data, which were obtained over a 90" X 90" field of view with a cadence of 10 sec. We also analyze simultaneous data from the Atmospheric Imaging Assembly and Extreme Ultraviolet Variability Experiment instruments on board the Solar Dynamics Observatory spacecraft, and data from Reuven Ramaty High Energy Solar Spectroscopic Imager and GOES spacecrafts. Non-thermal effects are ignored in this analysis. Several quantitative aspects of the data, as well as models derived using the "0D" Enthalpy-Based Thermal Evolution of Loops model (EBTEL: Klimchuk et al. 2008) code, indicate that the triplet states of the 10830 \AA\ multiplet are populated by photoionization of chromospheric plasma followed by radiative recombination. Surprisingly, the He II 304 \AA\ line is reasonably well matched by standard emission measure calculations, along with the C IV emission which dominates the AIA 1600 \AA\ channel during flares. This work lends support to some of our previous work combining X-ray, EUV and UV data of flares to build models of energy transport from corona to chromosphere.