ON THE FINE STRUCTURE SPLITTING OF THE 3p⁴3d ⁴D_5/2 AND 3p⁴3d ⁴D_7/2 LEVELS OF Fe x

Abstract

We study UV spectra obtained with the SO82-B slit spectrograph on board SKYLAB to estimate the fine structure splitting of the Cl-like 3p 4 3d 4 D 5/2 and 3p 4 3d 4 D 7/2 levels of Fe X. The splitting is of interest because the Zeeman effect mixes these levels, producing a "magnetically induced transition" (MIT) from 3p 4 3d 4 D 7/2 to 3p 5 2 P o 3/2 for modest magnetic field strengths characteristic of the active solar corona. We estimate the splitting using the Ritz combination formula applied to two lines in the UV region of the spectrum close to 1603.2Å, which decay from the level 3p 4 ( 1 D)3d 2 G 7/2 to these two lower levels. The MIT and accompanying spin-forbidden transition lie near 257Å. By careful inspection of a deep exposure obtained with the S082B instrument we derive a splitting of ∼ < 7 ± 3 cm −1 . The upper limit arises because of a degeneracy between the effects of non-thermal line broadening and fine-structure splitting for small values of the latter parameter. Although the data were recorded on photographic film, we solved for optimal values of line width and splitting of 8.3 ± 0.9 and 3.6 ± 2.7 cm −1 .

Solar UV and X-ray spectral diagnostics

“…Judge et al. (2016) carried out a similar analysis of the same Skylab observations to obtain . A similar energy difference was estimated from recent EBIT measurements (Li et al.…”

A first spectroscopic measurement of the magnetic field strength for an active region of the solar corona

“…For the important ∆E parameter introduced in Eq. 1 we use value of 3.6 cm −1 from the most accurate determination to date (Judge et al 2016). The two transition rates required to model the MIT spectral line are (Wang et al 2020),…”

“…To address this, we have over the past few years been investigating a spectroscopic method based on quantuminterference effects in the Fe 9+ ion (Li et al 2015(Li et al , 2016Judge et al 2016;Si et al 2020). This particular interference is caused by magnetic fields external to the ion, and hence this idea has the potential to act as a probe of the coronal field strengths.…”

“…A search for an atomic system involving a suitable pseduo-degeneracy was initiated a few years ago (Li et al 2015(Li et al , 2016Judge et al 2016;Si et al 2020), motivated by its potential as a magnetic-field probe. This led to the discovery of Fe 9+ where the excited levels 3p 4 3d 4 D 5/2 and 4 D 7/2 fulfill the requirements of being very close in energy and having significantly different lifetimes.…”

Measurements of Coronal Magnetic Field Strengths in Solar Active Region Loops

“…The Zeeman effect due to the magnetic field mixes the 4 D 5/2 and 4 D 7/2 levels, and opens a new pathway to the ground state. The idea was first proposed by Li et al (2015) and discussed further by Li et al (2016) and Judge et al (2016). Si et al (2020) and Landi et al (2020) subsequently developed techniques to enable measurements using observations by the Hinode (Kosugi et al 2007) EUV Imaging Spectrometer (EIS, Culhane et al 2007).…”