Photospheric and Coronal Abundances in an X8.3 Class Limb Flare
2018
We analyze solar elemental abundances in coronal post-flare loops of an X8.3 flare (SOL2017-09-10T16:06)
observed on the west limb on 2017 September 10 near 18 UT using spectra recorded by the Extreme-ultraviolet
Imaging Spectrometer (EIS) on the Hinode spacecraft. The abundances in the corona can differ from photospheric
abundances due to the first ionization potential (FIP) effect. In some loops of this flare, we find that the abundances
appear to be coronal at the loop apices or cusps, but steadily transform from coronal to photospheric as the loop
footpoint is approached. This result is found from the intensity ratio of a low-FIP ion spectral line (Ca XIV) to a
high-FIP ion spectral line (Ar XIV) formed at about the same temperature (4–5 MK). Both lines are observed close
in wavelength. Temperature, which could alter the interpretation, does not appear to be a factor based on intensity
ratios of Ca XV lines to a Ca XIV line. We discuss the abundance result in terms of the Laming model of the FIP
effect, which is explained by the action of the ponderomotive force in magnetohydrodynamic (MHD) waves in
coronal loops and in the underlying chromosphere.
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