Emission lines of Fe xv in spectra obtained with the Solar Extreme-Ultraviolet Research Telescope and Spectrograph

Abstract

Recent R-matrix calculations of electron impact excitation rates in Mg-like Fe XV are used to derive theoretical emission-line ratios involving transitions in the 243‐418 A wavelength range. A comparison of these with a data set of solar active region, subflare and off-limb spectra, obtained during rocket flights by the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS), reveals generally very good agreement between theory and observation, indicating that most of the Fe XV emission lines may be employed with confidence as electron density diagnostics. In particular, the 312.55-A line of Fe XV is not significantly blended with aC oXVII transition in active region spectra, as suggested previously, although the latter does make a major contribution in the subflare observations. Most of the Fe XV transitions which are blended have had the species responsible clearly identified, although there remain a few instances where this has not been possible. We briefly address the long-standing discrepancy between theory and experiment for the intensity ratio of the 3s 21 S‐3s3p 3 P1 intercombination line at 417.25 A to the 3s 21 S‐3s3p 1 P resonance transition at 284.16 A. Ke yw ords: atomic data ‐ Sun: activity ‐ Sun: flares ‐ ultraviolet: general.