2009A&A...508..401C

The analysis of the high-resolution UVES spectra of the CP stars HR6000 and 46Aql has revealed the presence of an impressive number of unidentified lines, in particular in the 5000-5400Å region. Because numerous 4d-4f transitions of FeII lie in this spectral range, and because both stars are iron overabundant, we investigate whether the unidentified lines are FeII. ATLAS12 model atmospheres with parameters T_eff=13450K, logg=4.3 and T_eff=12560K, logg=3.8 were computed for the individual abundances of the stars HR 6000 and 46 Aql, respectively, to use them as spectroscopic sources to identify FeII lines and determine FeII gf-values. After identifying several unknown lines in the stellar spectra as (³H)4d-(³H)4f transitions of FeII, we derived astrophysical loggf-values for them. The energies of the upper levels were assigned on the basis of both laboratory iron spectra and predicted energy levels. We determined 21 new levels of FeII with energies between 122910.9cm^–1 and 123441.1cm^–1. They allowed us to add 1700 new lines to the FeII linelist in the wavelength range 810-15011Å. Many of these lines are sufficiently strong to contribute to the spectra of PopulationI late B-type stars, even when their iron abundance is subsolar. In the 5000-6000Å region discussed in this paper, the astrophysical and computed loggf-values show good general agreement and greatly improve the synthetic spectrum of both HR 6000 and 46 Aql. However, many features remain unidentified indicating that further work to classify FeII high energy levels has still to be done