Coronal FeIX line intensities and electron density diagnostics

The relative intensities of the most prominent extreme-ultraviolet lines of Fe IX, seen in the outer atmospheres of the Sun and other stars, have been shown to be inconsistent with the best available atomic data. The density- sensitive Fe IX lambda 241.7/lambda 244.9 line intensity ratio, for example , yields electron densities in the solar corona that disagree with those ob tained from ratios in other ions, particularly at higher densities. We show here that these differences can be largely removed by using newly calculat ed atomic data, in particular electron impact collision strengths that incl ude pronounced resonance features, and by incorporating a measure of line e xcitation by collisional excitation and cascading.