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For the spectral analysis of high-resolution and high-signal-to-noise spectraof hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) modelatmospheres are mandatory. These are strongly dependent on the reliability ofthe atomic data that is used for their calculation.  To search for Zr and Xe lines in the ultraviolet (UV) spectra of G191-B2B andRE0503-289, new Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths werecalculated. This allows for the first time, determination of the Zr abundancein white dwarf (WD) stars and improvement of the Xe abundance determinations.  We calculated Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths toconsider radiative and collisional bound-bound transitions of Zr and Xe in ourNLTE stellar-atmosphere models for the analysis of their lines exhibited in UVobservations 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 thespectrum of RE0503-289. Zr was detected for the first time in a WD. We measureda Zr abundance of -3.5 +/- 0.2 (logarithmic mass fraction, approx. 11 500 timessolar). 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 Alabundance of -4.3 +/- 0.2 (solar) in RE0503-289. In the spectra of G191-B2B, noZr line was identified. The strongest Zr IV line (1598.948 A) in our model gavean upper limit of -5.6 +/- 0.3 which is about 100 times solar. No Xe line wasidentified in the UV spectrum of G191-B2B and we confirmed the previouslydetermined upper limit of -6.8 +/- 0.3 (ten times solar).  Precise measurements and calculations of atomic data are a prerequisite foradvanced NLTE stellar-atmosphere modeling. Observed Zr IV - VI and Xe VI - VIIline profiles in the UV spectrum of RE0503-289 were simultaneously wellreproduced.

astronomy and astrophysics

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