New Fe II energy levels from stellar spectra

TL;DR

This study identified 109 new Fe II energy levels using stellar spectra, significantly improving the identification of spectral lines in B-type and early A-type stars, especially in the optical range.

Contribution

The paper introduces a comprehensive set of newly identified Fe II energy levels derived from stellar spectra, enhancing spectral line identification accuracy.

Findings

Identified 109 new Fe II energy levels.

Over 50% of previously unidentified lines in HR 6000 explained.

Produced 18000 spectral lines from ultraviolet to infrared.

Abstract

The spectra of B-type and early A-type stars show mumerous unidentified lines in the whole optical range, especially in the 5100-5400 A interval. Because Fe II transitions to high energy levels should be observed in this region, we used semiempirical predicted wavelengths and gf-values of Fe II to identify unknown lines. Semiempirical line data for Fe II computed by Kurucz are used to synthesize the spectrum of the slow-rotating, Fe-overabundant CP star HR 6000. We determined a total of 109 new 4f levels for Fe II with energies ranging from 122324 cm^-1 to 128110 cm^-1. They belong to the Fe II subconfigurations 3d^6(^3P)4f (10 levels), 3d^6(^3H)4f (36 levels), 3d^6(^3F)4f (37 levels), and 3d^6(^3G)4f (26 levels). We also found 14 even levels from 4d (3 levels), 5d (7 levels), and 6d (4 levels) configurations. The new levels have allowed us to identify more than 50% of the previously unidentified lines of HR 6000 in the wavelength region 3800-8000 A. Tables listing the new energy levels are given in the paper; tables listing the spectral lines with log gf >/= -1.5 that are transitions to the 4f energy levels are given in the Online Material. These new levels produce 18000 lines throughout the spectrum from the ultraviolet to the infrared.