CHIANTI : an atomic database for emission lines II . Comparison with the SERTS - 89 active region spectrum

The CHIANTI database was described by Dere et al. (1997, hereafter Paper I) and the present paper applies the atomic data to the study of extreme ultraviolet emission lines found in the SERTS-89 active region spectrum published by Thomas & Neupert (1994). Firstly, the emission line ratios that are insensitive to density and temperature are used to check both the quality of the atomic data and the calibration of the instrument. Secondly, we use, where possible, ratios that are sensitive to density to estimate the electron density from different ions. In general we find excellent agreement between theory and observation, providing confidence in both the atomic data in the CHIANTI database and the quality of the SERTS-89 spectrum. Where inconsistencies between theory and observation exist we try to explain them in terms of either inaccuracies in the atomic data or blending of the lines. One consistent discrepancy was that all observed lines that we analysed in the 430–450Å region were uniformly a factor of 1.5–2.0 weaker than predicted, suggesting that the SERTS-89 calibration may need adjustment in this spectral interval. Serious problems were also found in some of the theoretical predictions for a few ions, especially Fe xiv.