Stellar laboratories VII. New Kr iv vii oscillator strengths and an improved spectral analysis of the hot, hydrogen deficient DO type white dwarf RE 0503 289
Context. 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. Aims. New Kr iv vii oscillator strengths for a large number of lines enable us to construct more detailed model atoms for our NLTE model atmosphere calculations. This enables us to search for additional Kr lines in observed spectra and to improve Kr abundance determinations. Methods. We calculated Kr iv vii oscillator strengths to consider radiative and collisional bound bound transitions in detail in our NLTE stellar atmosphere models for the analysis of Kr lines that are exhibited in high resolution and high S/N ultraviolet (UV) observations of the hot white dwarf RE 0503 289. Results. We reanalyzed the effective temperature and surface gravity and determined T eff 70000 2000 K and log g cm s 2 7.5 0.1. We newly identified ten Kr v lines and one Kr vi line in the spectrum of RE 0503 289. We measured a Kr abundance of 3.3 0.3 (logarithmic mass fraction) We discovered that the interstellar absorption toward RE 0503 289 has a multi velocity structure within a radial velocity interval of 40 km s 1 v rad 1 Conclusions. Reliable measurements and calculations of atomic data are a prerequisite for state of the art NLTE stellar atmosphere modeling. Observed Kr v vii line profiles in the UV spectrum of the white dwarf RE 0503 289 were simultaneously well reproduced with our newly calculated oscillator strengths.