Astronomy and Astrophysics, volume 566A, 10-10 (2014/6-1)
Stellar laboratories. III. New Ba V, Ba VI, and Ba VII oscillator strengths and the barium abundance in the hot white dwarfs G191-B2B and RE 0503-289.
RAUCH T., WERNER K., QUINET P. and KRUK J.W.
Abstract (from CDS):
For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation. Reliable BaV-VII oscillator strengths are used to identify Ba lines in the spectra of the DA-type white dwarf G191-B2B and the DO-type white dwarf RE0503-289 and to determine their photospheric Ba abundances. We newly calculated BaV-VII oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for the analysis of Ba lines exhibited in high-resolution and high-S/N UV observations of G191-B2B and RE0503-289. For the first time, we identified highly ionized Ba in the spectra of hot white dwarfs. We detected BaVI and BaVII lines in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of RE0503-289. The BaVI/BaVII ionization equilibrium is well reproduced with the previously determined effective temperature of 70000K and surface gravity of logg=7.5. The Ba abundance is 3.5±0.5x10–4 (mass fraction, about 23000 times the solar value). In the FUSE spectrum of G191-B2B, we identified the strongest BaVII line (at 993.41Å) only, and determined a Ba abundance of 4.0±0.5x10–6 (about 265 times solar). Reliable measurements and calculations of atomic data are a pre-requisite for stellar-atmosphere modeling. Observed BaVI-VII line profiles in two white dwarfs' (G191-B2B and RE0503-289 far-ultraviolet spectra were well reproduced with our newly calculated oscillator strengths. This allowed to determine the photospheric Ba abundance of these two stars precisely.