Atomic data for the X-ray lines of Fe VIII and Fe IX

Abstract

The distorted wave extension of the autostructure code has been used to calculate energy levels, radiative transition probabilities and collisional excitation rates of Fe VIII and Fe IX up to n = 6 for Fe IX and n = 7 for Fe VIII. We have compared some of the data with previous calculations, finding overall agreement for radiative transition rates, but interesting differences for some collisional data. We have merged our data for the higher energy levels with published R-matrix collisional excitation rates for the lower ones to calculate spectral line intensities and compare them with observations. In particular, we have focused on the transitions from high energy levels of Fe VIII & Fe IX which are present in the 93-95 Å region. A few new identifications are tentatively provided. We find that Fe IX 5f-3d and Fe VIII 7f-3d transitions only comprise a small fraction of the observed lines in the 93-95 Å region for quiet Sun conditions, and thus their contribution to the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94 Å band is expected to be small. © 2012 ESO.