THE SOLAR FLARE IRON ABUNDANCE

• Published in: The Astrophysical journal Vol. 748; no. 1; pp. 1 - 10
• Main Authors: PHILLIPS, K. J. H, DENNIS, B. R
• Format: Journal Article
• Language: English
• Published: Bristol IOP 20.03.2012
• Subjects: ABUNDANCE; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Data processing; Earth, ocean, space; Exact sciences and technology; Flares; Fractionation; GAMMA RADIATION; IRON; SOLAR FLARES; Spectra; Spectral emissivity; SUN; X RADIATION; X-RAY SPECTRA; Sun: flares; Plasma; Data analysis; gamma rays; Solar flares; Sun: abundances; Line identification; Sun: corona; Spectral model; X-ray spectra; Quiet sun; Solar abundance; Gamma radiation; Sun: X-rays; Emission line; line: identification
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/748/1/52

The abundance of iron is measured from emission line complexes at 6.65 keV (Fe line) and 8 keV (Fe/Ni line) in RHEssI X-ray spectra during solar flares. Spectra during long-duration flares with steady declines were selected, with an isothermal assumption and improved data analysis methods over previous work. Two spectral fitting models give comparable results, viz., an iron abundance that is lower than previous coronal values but higher than photospheric values. In the preferred method, the estimated Fe abundance is A(Fe) = 7.91 + or - 0.10 (on a logarithmic scale, with A(H) = 12) or 2.6 + or - 0.6 times the photospheric Fe abundance. Our estimate is based on a detailed analysis of 1898 spectra taken during 20 flares. No variation from flare to flare is indicated. This argues for a fractionation mechanism similar to quiet-Sun plasma. The new value of A(Fe) has important implications for radiation loss curves, which are estimated.