New identified (3H)4d - (3H)4f transitions of Fe II from UVES spectra of HR 6000 and 46 Aql

TL;DR

This study identified numerous new (3H)4d - (3H)4f transitions of Fe II in the spectra of HR 6000 and 46 Aql, expanding the Fe II line list and improving spectral line identification.

Contribution

The paper reports the first identification of 21 new Fe II energy levels and 1700 new lines in the UV range, based on high-resolution spectra and model atmospheres.

Findings

Identified 21 new Fe II energy levels.

Added 1700 new Fe II lines to the spectral database.

Improved understanding of Fe II transitions in stellar spectra.

Abstract

The analysis of the high-resolution UVES spectra of the CP stars HR 6000 and 46 Aql revealed the presence of an impressive number of unidentified lines, in particular in the 5000 - 5400 A region. Because numerous 4d-4f transitions of FeII lie in this spectral range, and because both stars are iron overabundant, we investigated whether the unidentified lines can be due to FeII. ATLAS12 model atmospheres with parameters [13450K, 4.3] and [12560K, 3.8] were computed for the individual abundances of HR 6000 and 46 Aql, respectively, in order to use the stars as spectroscopic sources to identify FeII lines and to determine FeII gf-values. After having identified several unknown lines in the stellar spectra as due to (3H)4d - (3H)4f transitions of FeII, we derived stellar log gf's for them by comparing observed and computed profiles. The energies of the upper levels were assigned on the basis of both laboratory iron spectra and predicted energy levels. We fixed 21 new levels of FeII with energies between 122910.9 cm^-1 and 123441.1 cm^-1. They allowed us to add 1700 new lines to the Fe II line list in the range 810 - 15011 A.