Multi-passband Observations of a Solar Flare over the He i 10830 Å line

Document Type

Article

Publication Date

1-1-2022

Abstract

This study presents a C3.0 flare observed by the Big Bear Solar Observatory/Goode Solar Telescope (GST) and Interface Region Imaging Spectrograph (IRIS) on 2018 May 28 around 17:10 UT. The Near-Infrared Imaging Spectropolarimeter of GST was set to spectral imaging mode to scan five spectral positions at 0.8, 0.4 Å and line center of He i 10830 Å. At the flare ribbon's leading edge, the line is observed to undergo enhanced absorption, while the rest of the ribbon is observed to be in emission. When in emission, the contrast compared to the preflare ranges from about 30% to nearly 100% at different spectral positions. Two types of spectra, "convex"shape with higher intensity at line core and "concave"shape with higher emission in the line wings, are found at the trailing and peak flaring areas, respectively. On the ribbon front, negative contrasts, or enhanced absorption, of about ~10%-20% appear in all five wavelengths. This observation strongly suggests that the negative flares observed in He i 10830 Å with mono-filtergram previously were not caused by pure Doppler shifts of this spectral line. Instead, the enhanced absorption appears to be a consequence of flare-energy injection, namely nonthermal collisional ionization of helium caused by the precipitation of high-energy electrons, as found in our recent numerical modeling results. In addition, though not strictly simultaneous, observations of Mg ii from the IRIS spacecraft, show an obvious central reversal pattern at the locations where enhanced absorption of He i 10830 Å is seen, which is consistent with previous observations.

Identifier

85123248330 (Scopus)

Publication Title

Astrophysical Journal Letters

External Full Text Location

https://doi.org/10.3847/2041-8213/ac447c

e-ISSN

20418213

ISSN

20418205

Issue

1

Volume

924

Grant

PTDC/CCI-BIO/29266/2017

Fund Ref

Fundação para a Ciência e a Tecnologia

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