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^{⋆,⋆⋆,⋆⋆⋆,⋆⋆⋆⋆,†}

¹ Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, 72076 Tübingen, Germany
e-mail: rauch@astro.uni-tuebingen.de
² Physique Atomique et Astrophysique, Université de Mons – UMONS, 7000 Mons, Belgium
³ IPNAS, Université de Liège, Sart Tilman, 4000 Liège, Belgium
⁴ Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Golm, Germany
⁵ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁶ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁷ Astronomisches Rechen-Institut (ARI), Centre for Astronomy of Heidelberg University, Mönchhofstraße 12-14, 69120 Heidelberg, Germany

Received: 14 January 2016
Accepted: 21 February 2016

Abstract

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< + 18 km s^-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.