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

Abstract

Aims. The analysis of the high-resolution UVES spectra of the CP stars HR6000 and 46 Aql has revealed the presence of an impressive number of unidentified lines, in particular in the 5000-5400Å. Because numerous 4d-4f transitions of Fe II lie in this spectral range, and because both stars are iron overabundant, we investigate whether the unidentified lines are Fe II. Methods. ATLAS12 model atmospheres with parameters Teff =13450K, log g=4.3 and Teff=12560K, log g=3.8 were computed for the individual abundances of the stars HR6000 and 46Aql, respectively, to use them as spectroscopic sources to identify Fe II lines and determine Fe II gf-values. After identifying several unknown lines in the stellar spectra as ( 3H)4d-(3H)4f transitions of Fe II, we derived astrophysical log gf-values for them. The energies of the upper levels were assigned on the basis of both laboratory iron spectra and predicted energy levels. Results. We determined 21 new levels of Fe II with energies between 122910.9cm-1 and 123441.1cm-1. They allowed us to add 1700 new lines to the Fe II 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 5000-6000 Å region discussed in this paper, the astrophysical and computed log gf-values show good general agreement and greatly improve the synthetic spectrum of both HR6000 and 46Aql. However, many features remain unidentified indicating that further work to classify Fe II high energy levels has still to be done. © 2009 ESO.