A Comparison between Coronal Emission Lines from an Isothermal Spectrum Observed with the Coronal Diagnostic Spectrometer and CHIANTI Emissivities
The present paper compares off-disk spectral observations of the solar corona in the ranges 307-379 and 513-633 Å with theoretical emissivities calculated using the CHIANTI database. The observed spectra were recorded by the Coronal Diagnostic Spectrometer instrument on board the Solar and Heliospheric Observatory using the normal-incidence portion of the instrument. Using line-ratio techniques, we first measure the electron temperature and density in the emitting region, verifying that it is nearly isothermal. Next, we use an emission-measure analysis to compare measured spectral line intensities with predictions from the CHIANTI database. This comparison allows us to assess the quality of the CHIANTI data for the brightest coronal lines in the 307-379 and 513-633 Å spectral ranges. As a result, we are able to (1) select lines and ions for which the agreement between theory and observation is good, (2) identify a few lines that are blended, and (3) stress inconsistencies between a few lines and theory, thus showing where improvements to atomic data and transition probabilities are necessary.