Coronal Fe ix 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 λ 241.7/ λ 244.9 line intensity ratio, for example, yields electron densities in the solar corona that disagree with those obtained from ratios in other ions, particularly at higher densities. We show here that these differences can be largely removed by using newly calculated atomic data, in particular electron impact collision strengths that include pronounced resonance features, and by incorporating a measure of line excitation by collisional excitation and cascading.