Atomic data for astrophysics : Fe IX

Del Zanna, G. and Storey, P.J. and Badnell, N.R. and Mason, H.E. (2014) Atomic data for astrophysics : Fe IX. Astronomy and Astrophysics, 565. A77. ISSN 0004-6361

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    We present the results of a new large-scale intermediate-coupling frame transformation R-matrix scattering calculation for electron collisional excitation of Fe ix. The target includes all the main configurations up to n = 5, to improve our earlier R-matrix and distorted-wave (DW) calculations for the n = 3,4 levels. Unlike similar calculations which we carried out for the other coronal iron ions, in this case the larger target does not significantly affect the collision strengths of the strongest transitions to the n = 3,4 levels. Some differences are however present for a few transitions, in particular for the 3d–4p line at 197.86 Å. For the weaker transitions, significant enhancements due to extra resonances resulting from this much bigger target are found. Several new line identifications are suggested. We find excellent agreement between predicted and observed line intensities in the EUV (Hinode EIS) showing that Fe ix lines provide a reliable temperature diagnostic. We also show that the visible forbidden lines are a good diagnostic to measure electron densities.