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

0557401 - ASÚ 2023 RIV GB eng J - Journal Article
Del Zanna, G. - Polito, V. - Dudík, Jaroslav - Testa, P. - Mason, H. E. - Dzifčáková, Elena
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. Roč. 930, č. 1 (2022), č. článku 61. ISSN 0004-637X. E-ISSN 1538-4357
R&D Projects: GA ČR GA20-07908S; GA ČR(CZ) GA22-07155S
Institutional support: RVO:67985815
Keywords : benchmarking atomic data * optically thin spectra * kappa-distributions
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 4.9, year: 2022
Method of publishing: Open access

We present joint Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) and Interface Region Imaging Spectrograph (IRIS) observations of Fe xii 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 angstrom/1349 angstrom 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 xii 193 and 195 angstrom lines, but not in the 192.4 angstrom line, in agreement with previous findings. As we cannot rule out possible EUV absorption by H, He, and He ii 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 xii 192.4 angstrom/1349 angstrom 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.
Permanent Link: http://hdl.handle.net/11104/0331628