Atomic data for astrophysics : Fe X soft x-ray lines

New atomic calculations for Fe x are presented. They focus on the need to model the soft X-ray spectrum and in particular the line at 94.0 Å which is the dominant contribution to the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94 Å band in quiet Sun conditions. This line, and others in the band, are due to strong decays from n = 4 levels. We present new large-scale R-matrix (up to n = 4) and distorted-wave (DW, up to n = 6) scattering calculations for electron collisional excitation and compare them to earlier work. We find significant discrepancies with previous calculations. We show that resonances significantly increase the cross-sections for excitations from the ground state to some n = 4 levels, in particular to those in the 3s2 3p4 4s configuration. Cascading from higher levels is also important. We suggest a new identification for the 3s 3p62S1/2–3s 3p5 4s 2P3/2 transition, that has a predicted intensity larger than the decays from the 3s2 3p4 4s levels which were identified by Edlén in 1936. The results presented here are relevant to our understanding of transitions from n = 4 levels in a wide range of other ions