Spectral diagnostics of cool flare loops observed by SST: I. Inversion of the Ca II 8542 Å and H\(\beta\) lines

Flare loops form an integral part of eruptive events, being detected in the range of temperatures from X-rays down to cool chromospheric-like plasmas. While the hot loops are routinely observed by the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA), cool loops seen off-limb...

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Veröffentlicht in:arXiv.org 2019-09
Hauptverfasser: Koza, Július, Kuridze, David, Heinzel, Petr, Jejčič, Sonja, Morgan, Huw, Zapiór, Maciej
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Sprache:eng
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Zusammenfassung:Flare loops form an integral part of eruptive events, being detected in the range of temperatures from X-rays down to cool chromospheric-like plasmas. While the hot loops are routinely observed by the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA), cool loops seen off-limb are rare. In this paper we employ unique observations of the SOL2017-09-10T16:06 X8.2-class flare which produced an extended arcade of loops. The Swedish 1-m Solar Telescope (SST) made a series of spectral images of the cool off-limb loops in the Ca II 8542 Å and the hydrogen H\(\beta\) lines. Our focus is on the loop apices. Non-LTE spectral inversion is achieved through the construction of extended grids of models covering a realistic range of plasma parameters. The Multilevel Accelerated Lambda Iterations (MALI) code solves the non-LTE radiative-transfer problem in a 1D externally-illuminated slab, approximating the studied loop segment. Inversion of the Ca II 8542 Å and H\(\beta\) lines yields two similar solutions, both indicating high electron densities around \(2 \times 10^{12}\) cm\(^{-3}\) and relatively large microturbulence around 25 kms\(^{-1}\). These are in reasonable agreement with other independent studies of the same or similar events. In particular, the high electron densities in the range \(10^{12} - 10^{13}\) cm\(^{-3}\) are consistent with those derived from the SDO's Helioseismic and Magnetic Imager white-light observations. The presence of such high densities in solar eruptive flares supports the loop interpretation of the optical continuum emission of stars which manifest superflares.
ISSN:2331-8422
DOI:10.48550/arxiv.1909.07356