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

Recent R-matrix calculations of electron impact excitation rates in Mg-like FeXV are used to derive theoretical emission-line ratios involving transitions in the 243-418 Åwavelength 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 FeXV emission lines may be employed with confidence as electron density diagnostics. In particular, the 312.55-Åline of FeXV is not significantly blended with a CoXVII transition in active region spectra, as suggested previously, although the latter does make a major contribution in the subflare observations. Most of the FeXV 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 3s²¹S-3s3p ³P₁ intercombination line at 417.25 Åto the 3s²¹S-3s3p ¹P resonance transition at 284.16 Å....