New Fe ii energy levels from stellar spectra ^*

¹ Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy e-mail: castelli@oats.inaf.it
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received: 1 June 2010
Accepted: 29 June 2010

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 HR 6000.

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), 3d⁶(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 HR 6000 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 gf ≥ -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.