X-Ray Line Ratios for Fe XVII Observed in the Solar Corona.
AEROSPACE CORP EL SEGUNDO CA SPACE SCIENCES LAB
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Selected solar spectra from the SOLEX B X-ray spectrometers aboard the USAF P78-1 satellite were analyzed in order to compare Fe XVII line flux ratios with theory. The spectra were chosen to cover a wide range of solar activity from quiescent active regions to large flares. For purposes of comparison with theory, a temperature scale based on a ratio of Fe XVIII to Fe XVII line fluxes has been derived. Fe XVII line ratios involving one line with a 3s outer electron in the upper state and the other with a 3d electron are potentially the most useful, since such ratios are predicted, by theory, to have a significant temperature dependence. The data do not support the theoretical predictions. The dependence of the 3s3d line ratios on temperature is found to be very weak, and the ratios are unlikely to be useful as temperature diagnostics. Measurements of the ratios involving only 3s upper levels or only 3d upper levels also disagree with theory. Improved theoretical calculations are needed to interpret the large amount of high-quality data that are now becoming available. Keywords Solar flares Line spectra Solar X ray spectra Resonance scattering.