Revised Analysis of Fe vii

Alexander Kramida,Alexander N Ryabtsev,Peter R Young

doi:10.3847/1538-4365/ac3a7e

Abstract

Abstract New spectrograms of multiply ionized iron have been recorded and analyzed, targeting the Fe vii spectrum. As a result, several previously unknown spectral lines and energy levels have been identified in this spectrum. These new data have been analyzed together with all previously published laboratory and astrophysical data on this spectrum. The energy levels have been interpreted using parametric calculations with Cowan codes. Radiative transition rates calculated in this work supplemented other previously published calculations in constructing a complete set of recommended transition probabilities. The ionization energy of Fe vii has been redetermined with a fivefold improvement in accuracy. Its new value is 1,007,928(20) cm−1, corresponding to 124.9671(25) eV.

Highlights

Six times ionized iron (Fe VII) belongs to the calcium isoelectronic sequence with a 3p63d2 ground state electronic configuration
The Fe VII spectrum analysis was guided by calculations of the energy levels and transition probabilities with a suite of Cowan codes (Cowan 1981; Kramida 2019)
Since no energy levels involving excitation from the 3s and lower electronic shells have been observed in experiments, the designations of the complete [Ne]3s2 core shells are omitted from level labels in the subsequent text and Table 5

Summary

Introduction

Six times ionized iron (Fe VII) belongs to the calcium isoelectronic sequence with a 3p63d2 ground state electronic configuration. The nine fine-structure levels of the ground configuration give rise to several forbidden transitions in the visible that become prominent in hot, low-density astrophysical plasmas. The fine-structure transitions within the ground 4F term give lines at 7.8 μm and 9.5 μm that have been observed with the Infrared Space Observatory (Feuchtgruber et al 1997). We show an Fe VII spectrum generated with version 10 of the CHIANTI database (Del Zanna et al 2021) assuming a temperature of 0.4 MK, an electron number density of 8 × 108 cm−3, and solar photospheric abundances. The strongest lines are found between 140 and 320 Å and arise from allowed 3p–3d, 3d–4p, 3d–4f, and forbidden 3d–4s transitions. Between 650 and 1350 Å, there are weaker lines due to 4s–4p, 4p–4d, and 4d–4f transitions

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