New Fe II energy levels from stellar spectra

Abstract

Aims. The spectra of B-type and early A-type stars show numerous unidentified lines in the whole optical range, especially in the 5100-5400 Å 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. Methods. Semiempirical line data for Fe ii computed by Kurucz are used to synthesize the spectrum of the slow-rotating, Fe -overabundant CP star HR6000. Results. We determined a total of 109 new 4f levels for Fe ii with energies ranging from 122 324 cm -1 to 128 110 cm-1. They belong to the Fe ii subconfigurations 3d6(3P)4f (10 levels), 3d 6(3H)4f (36 levels), 3d6( 3F)4f (37 levels), and 3d6(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 HR6000 in the wavelength region 3800-8000 Å. Tables listing the new energy levels are given in the paper; tables listing the spectral lines with log g f = ≥1.5 that are transitions to the 4f energy levels are given in the Online Material. These new levels produce 18 000 lines throughout the spectrum from the ultraviolet to the infrared. © 2010 ESO.