2010A&A...520A..57C

The spectra of B-type and early A-type stars show numerous unidentified lines in the whole optical range, especially in the 5100-5400Å interval. Because FeII transitions to high energy levels should be observed in this region, we used semiempirical predicted wavelengths and gf-values of FeII to identify unknown lines. Semiempirical line data for FeII computed by Kurucz are used to synthesize the spectrum of the slow-rotating, Fe-overabundant CP star HR6000. We determined a total of 109 new 4f levels for FeII with energies ranging from 122324/cm to 128110/cm. They belong to the FeII subconfigurations 3d⁶(³P)4f (10 levels), 3d⁶(³H)4f (36levels), 3d⁶(³F)4f (37levels), and 3d⁶(³G)4f (26levels). We also found 14 even levels from 4d (3levels), 5d (7levels), and 6d (4levels) configurations. The new levels have allowed us to identify more than 50% of the previously unidentified lines of HR6000 in the wavelength region 3800-8000Å. Tables listing the new energy levels are given in the paper; tables listing the spectral lines with loggf≥-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.