Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite

Mulay, S. M. and Fletcher, L. (2021) Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite. Monthly Notices of the Royal Astronomical Society, 504(2), pp. 2842-2852. (doi: 10.1093/mnras/stab367)

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Abstract

We have carried out the first comprehensive investigation of enhanced line emission from molecular hydrogen, H2 at 1333.79 Å, observed at flare ribbons in SOL2014-04-18T13:03. The cool H2 emission is known to be fluorescently excited by Si IV 1402.77 Å UV radiation and provides a unique view of the temperature minimum region (TMR). Strong H2 emission was observed when the Si IV 1402.77 Å emission was bright during the flare impulsive phase and gradual decay phase, but it dimmed during the GOES peak. H2 line broadening showed non-thermal speeds in the range 7-18 km s−1, possibly corresponding to turbulent plasma flows. Small red (blue) shifts, up to 1.8 (4.9) km s−1 were measured. The intensity ratio of Si IV 1393.76 Å and Si IV 1402.77 Å confirmed that plasma was optically thin to Si IV (where the ratio = 2) during the impulsive phase of the flare in locations where strong H2 emission was observed. In contrast, the ratio differs from optically thin value of 2 in parts of ribbons, indicating a role for opacity effects. A strong spatial and temporal correlation between H2 and Si IV emission was evident supporting the notion that fluorescent excitation is responsible.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay and Mulay, Dr Sargam
Authors: Mulay, S. M., and Fletcher, L.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Monthly Notices of the Royal Astronomical Society
Publisher:Oxford University Press
ISSN:0035-8711
ISSN (Online):1365-2966
Published Online:12 February 2021
Copyright Holders:Copyright © 2021 The Authors
First Published:First published in Monthly Notices of the Royal Astronomical Society 504(2): 2842-2852
Publisher Policy:Reproduced in accordance with the publisher copyright policy
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
173869Consolidated Grant in Solar PhysicsLyndsay FletcherScience and Technology Facilities Council (STFC)ST/P000533/1P&S - Physics & Astronomy
306515PHAS A&A Group STFC ConsolidatedLyndsay FletcherScience and Technology Facilities Council (STFC)ST/T000422/1P&S - Physics & Astronomy