Benchmarking atomic data for astrophysics: a first look at the soft X-ray lines

A collection of the best solar and laboratory spectra in the soft X-rays is used to perform a preliminary benchmark in this wavelength region, by comparing observed with predicted wavelengths and calibrated solar irradiances. The benchmark focuses on the Fe IX - Fe XIV ions, for which we have recently calculated the relevant atomic data; however, a few other ions have also been benchmarked. The iron ions dominate the soft X-rays, however a large fraction of the strongest soft X-ray lines due to n = 4 -> n = 3 transitions were previously unidentified. The strongest transitions are all identified here, in particular the decays from the core-excited levels (3s 3p(l) 4s, l = 5,4,3,2,1 for Fe X, Fe XI, Fe XII, Fe XIII, and Fe XIV, respectively), which are the strongest soft X-ray transitions from these ions. Many new identifications are proposed, some only tentatively. Good agreement in terms of solar irradiances between the soft-Xray and EUV (n = 3 -> n = 3) transitions is found, confirming the reliability of the new large-scale calculations. Some of the new atomic data and identifications are particularly important for the Solar Dynamic Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94 angstrom band.