CHIANTI—An Atomic Database for Emission Lines. V. Comparison with an Isothermal Spectrum Observed with SUMER

Abstract

CHIANTI is a database consisting of critically evaluated atomic dataand transition probabilities necessary to analyze spectral observationsof optically thin plasmas. Previous papers described the contentof the database and compared it to a solar active region spectrumbetween 170 and 450 Å. The aim of the present paper is to compareCHIANTI predictions to off-disk spectral observations of the solarcorona between 500 and 1500 Å. The observed spectra were recordedby the SUMER instrument on board the Solar and Heliospheric Observatoryusing the full spectral range allowed by the instrument. Earlierworks have demonstrated that the particular emitting plasma is isothermalat a temperature of 1.35 × 10 6 K, making it ideal for the assessmentof the accuracy of the CHIANTI database. This assessment of the CHIANTIdatabase allowed us (1) to select lines and ions for which the agreementbetween theory and observation is good, (2) to identify several lineswhich are blended, and (3) to stress inconsistencies between a fewlines and theory, thus showing where improvements to atomic dataand transition probabilities are necessary.