Mulay, S. M. , Fletcher, L. , Hudson, H. and Labrosse, N. (2023) Behaviour of molecular hydrogen emission in three solar flares. Monthly Notices of the Royal Astronomical Society, 526(3), pp. 4755-4767. (doi: 10.1093/mnras/stad2853)
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Abstract
We have systematically investigated ultraviolet (UV) emission from molecular hydrogen (H2) using the Interface Region Imaging Spectrometer (IRIS), during three X-ray flares of C5.1, C9.7 and X1.0 classes on Oct. 25, 2014. Significant emission from five H₂ spectral lines appeared in the flare ribbons, interpreted as photo-excitation (fluorescence) due to the absorption of UV radiation from two Si iv spectral lines. The H₂ profiles were broad and consisted of two non-stationary components in red and in the blue wings of the line in addition to the stationary component. The red (blue) wing components showed small red-shifts (blue-shifts) of ∼5–15 km s⁻¹ (∼5–10 km s⁻¹). The nonthermal velocities were found to be ∼5–15 km s⁻¹. The interrelation between intensities of H₂ lines and their branching ratios confirmed that H₂ emission formed under optically thin plasma conditions. There is a strong spatial and temporal correlation between Si iv and H₂ emission, but the H₂ emission is more extended and diffuse, further suggesting H₂ fluorescence, and - by analogy with flare ‘back-warming’- providing a means to estimate the depth from which the H₂ emission originates. We find that this is 1871 ± 157 km and 1207 ± 112 km below the source of the Si iv emission, in two different ribbon locations.
| Item Type: | Articles |
|---|---|
| Additional Information: | SMM, LF and NL acknowledge support from UK Research and Innovation’s Science and Technology Facilities Council under grant award number ST/T000422/1 and ST/X000990/1. |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Labrosse, Dr Nicolas and Fletcher, Professor Lyndsay and Hudson, Dr Hugh and Mulay, Dr Sargam |
| Authors: | Mulay, S. M., Fletcher, L., Hudson, H., and Labrosse, N. |
| 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: | 10 October 2023 |
| Copyright Holders: | Copyright © 2023 The Authors |
| First Published: | First published in Monthly Notices of the Royal Astronomical Society 526(3):4755–4767 |
| Publisher Policy: | Reproduced under a Creative Commons License |
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