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

TL;DR

This study benchmarks atomic data for Fe IX - Fe XIV ions in the soft X-ray region using solar and laboratory spectra, identifying key transitions and confirming the accuracy of recent calculations, with implications for solar observation instruments.

Contribution

It provides the first comprehensive benchmark of atomic data for soft X-ray lines of Fe ions, identifying previously unknown transitions and validating new theoretical calculations.

Findings

Strong agreement between observed and predicted solar irradiances.

Identification of all strongest soft X-ray transitions from Fe ions.

New atomic data are crucial for interpreting SDO AIA 94 Å observations.

Abstract

A collection of the best solar and laboratory spectra in the soft X-rays is used here to perform a preliminary benchmark in this wavelength region, by comparing observed vs. 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 are dominating 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 X-ray 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 A band.