Emission Line Intensity Ratios of Fe xxvi/ xxv/ xxiv in Solar Flares Observed by Hinotori

Abstract

High-resolution spectra observed by the Solar X-ray spectrometer on board the Hinotori mission are revisited. Flat crystals slightly offset to the satellite spin axis produce automatic spectral scans for emission lines emerging from highly charged iron ions in solar flares every half-spin time period. All the downlinked data of the mission are converted to FITS format and major flare spectral data are revived as IDL save files in ISAS/DARTS. Based on these data sets, single-temperature fits are performed for the emission line complex of highly charged iron ions in the wavelength range of 1.75–1.95 Å and compared with theoretical predictions. Synthetic spectra with single electron temperatures estimated from j / w line-intensity ratios fit fairly well for Fe xxiv and Fe xxiii lines in the wavelength range of 1.85–1.88 Å, while intensity ratios of Fe xxv lines ( x , y , z ) and the inner-shell excitation line of Fe xxiv ( q ) to the Fe xxv resonance line ( w ) have systematic excesses. Empirical relations for the observed line ratios are derived. Ion fractions of Fe ^+25 /Fe ^+24 estimated by intensity ratios of Ly α /w in the temperature range of log T _e =7.25–7.45 are consistent with values in ionization equilibrium, and the remaining excesses of the Fe xxv line ratios may suggest problems with the atomic parameters or atomic modeling.

Keywords

• Solar x-ray emission
• Atomic spectroscopy
• Line intensities
• Atomic data