Diagnostics of Non-Maxwellian Electron Distributions in Solar Active Regions from Fe xii Lines Observed by the Hinode Extreme Ultraviolet Imaging Spectrometer and Interface Region Imaging Spectrograph
Publication Date
2022Journal Title
Astrophysical Journal
ISSN
0004-637X
Publisher
American Astronomical Society
Volume
930
Issue
1
Language
en
Type
Article
This Version
VoR
Metadata
Show full item recordCitation
Del Zanna, G., Polito, V., Dudík, J., Testa, P., Mason, H., & Dzifčáková, E. (2022). Diagnostics of Non-Maxwellian Electron Distributions in Solar Active Regions from Fe xii Lines Observed by the Hinode Extreme Ultraviolet Imaging Spectrometer and Interface Region Imaging Spectrograph. Astrophysical Journal, 930 (1) https://doi.org/10.3847/1538-4357/ac6174
Abstract
<jats:title>Abstract</jats:title>
<jats:p>We present joint Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) and Interface Region Imaging Spectrograph (IRIS) observations of Fe <jats:sc>xii</jats:sc> lines in active regions, both on-disk and off-limb. We use an improved calibration for the EIS data, and find that the 192.4 Å/1349 Å observed ratio is consistent with the values predicted by CHIANTI and the coronal approximation in quiescent areas, but not in all active-region observations, where the ratio is often lower than expected by up to a factor of about two. We investigate a number of physical mechanisms that could affect this ratio, such as opacity and absorption from cooler material. We find significant opacity in the EIS Fe <jats:sc>xii</jats:sc> 193 and 195 Å lines, but not in the 192.4 Å line, in agreement with previous findings. As we cannot rule out possible EUV absorption by H, He, and He <jats:sc>ii</jats:sc> in the on-disk observations, we focus on an off-limb observation where such absorption is minimal. After considering these, as well as possible nonequilibrium effects, we suggest that the most likely explanation for the observed low Fe <jats:sc>xii</jats:sc> 192.4 Å/1349 Å ratio is the presence of non-Maxwellian electron distributions in the active regions. This is in agreement with previous findings based on EIS and IRIS observations independently.</jats:p>
Keywords
360, The Sun and the Heliosphere
Sponsorship
Science and Technology Facilities Council (ST/P000665/1)
STFC (ST/T000481/1)
Identifiers
apjac6174, ac6174, aas36621
External DOI: https://doi.org/10.3847/1538-4357/ac6174
This record's URL: https://www.repository.cam.ac.uk/handle/1810/336857
Rights
Licence:
http://creativecommons.org/licenses/by/4.0/
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