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The solar photospheric-to-coronal Fe abundance ratio from X-ray fluorescence lines


  • K. J. H. Phillips

    Corresponding author
    1. Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH6 5NT
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The ratio of the Fe abundance in the photosphere to that in coronal flare plasmas is determined by X-ray lines within the complex at 6.7 keV (1.9 Å) emitted during flares. The line complex includes the He-like Fe (Fe xxv) resonance line w (6.70 keV) and Fe Kα lines (6.39 and 6.40 keV), the latter being primarily formed by the fluorescence of photospheric material by X-rays from the hot flare plasma. The ratio of the Fe Kα lines to the Fe xxvw depends on the ratio of the photospheric to flare Fe abundance, heliocentric angle θ of the flare and the temperature Te of the flaring plasma. Using high-resolution spectra from X-ray spectrometers on the P78-1 and Solar Maximum Mission spacecraft, the Fe abundance in flares is estimated to be 1.6 ± 0.5 and 2.0 ± 0.3 times the photospheric Fe abundance, the P78-1 value being preferred as it is more directly determined. This enhancement is consistent with results from X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft, but is significantly less than a factor of 4 as in previous work.

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