Stellar laboratories. VIII. New Zr IV - VII, Xe IV - V, and Xe VII oscillator strengths and the Al, Zr, and Xe abundances in the hot white dwarfs G191-B2B and RE0503-289

Abstract

For the spectral analysis of high-resolution and high-signal-to-noise 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. To search for Zr and Xe lines in the ultraviolet (UV) spectra of G191-B2B and RE0503-289, new Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths were calculated. This allows for the first time, determination of the Zr abundance in white dwarf (WD) stars and improvement of the Xe abundance determinations. We calculated Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths to consider radiative and collisional bound-bound transitions of Zr and Xe in our NLTE stellar-atmosphere models for the analysis of their lines exhibited in UV observations of the hot WDs G191-B2B and RE0503-289. We identified one new Zr IV, 14 new Zr V, and ten new Zr VI lines in the spectrum of RE0503-289. Zr was detected for the first time in a WD. We measured a Zr abundance of -3.5 +/- 0.2 (logarithmic mass fraction, approx. 11 500 times solar). We dentified five new Xe VI lines and determined a Xe abundance of -3.9 +/- 0.2 (approx. 7500 times solar). We determined a preliminary photospheric Al abundance of -4.3 +/- 0.2 (solar) in RE0503-289. In the spectra of G191-B2B, no Zr line was identified. The strongest Zr IV line (1598.948 A) in our model gave an upper limit of -5.6 +/- 0.3 which is about 100 times solar. No Xe line was identified in the UV spectrum of G191-B2B and we confirmed the previously determined upper limit of -6.8 +/- 0.3 (ten times solar). Precise measurements and calculations of atomic data are a prerequisite for advanced NLTE stellar-atmosphere modeling. Observed Zr IV - VI and Xe VI - VII line profiles in the UV spectrum of RE0503-289 were simultaneously well reproduced.

arXiv comment137 pages, 11 figures

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• 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 RE0503-289
• Stellar laboratories. VI. New Mo IV - VII oscillator strengths and the molybdenum abundance in the hot white dwarfs G191-B2B and RE0503-289
• Stellar laboratories: new Ge V and Ge VI oscillator strengths and their validation in the hot white dwarf RE 0503-289
• Stellar laboratories. VII. New Kr IV - VII oscillator strengths and an improved spectral analysis of the hot, hydrogen-deficient DO-type white dwarf RE0503-289
• Stellar laboratories II. New Zn IV and Zn V oscillator strengths and their validation in the hot white dwarfs G191-B2B and RE0503-289
• Stellar laboratories. V. The Xe VI ultraviolet spectrum and the xenon abundance in the hot DO-type white dwarf RE0503-289

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• Search for trans-iron elements in hot, helium-rich white dwarfs with the HST Cosmic Origins Spectrograph
• Stellar laboratories. X. New Cu IV - VII oscillator strengths and the first detection of copper and indium in hot white dwarfs
• Observations of the Ultraviolet-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205)
• Discovery of two bright DO-type white dwarfs
• Detection of cesium in the atmosphere of the hot He-rich white dwarf HD 149499B
• NLTE spectral analysis of the intermediate helium-rich subdwarf B star CPD-20°1123