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We present an analysis of high-dispersion and high signal-to-noise ratiospectra of the DAZ white dwarf GALEX J1931+0117. The spectra obtained with theVLT-Kueyen/UV-Visual Echelle Spectrograph show several well-resolved Si IIspectral lines enabling a study of pressure effects on line profiles. Weobserved large Stark shifts in silicon lines in agreement with laboratorymeasurements. A model atmosphere analysis shows that the magnesium, silicon andiron abundances exceed solar abundances, while the oxygen and calciumabundances are below solar. Also, we compared the observed line profiles tosynthetic spectra computed with variable accretion rates and vertical abundancedistributions assuming diffusion steady-state. The inferred accretion ratesvary from dM/dt=2x10^6 for calcium to 2x10^9 g/s for oxygen and indicate thatthe accretion flow is dominated by oxygen, silicon and iron while beingdeficient in carbon, magnesium and calcium. The lack of radial velocityvariations between two measurement epochs suggests that GALEX J1931+0117 isprobably not in a close binary and that the source of the accreted materialresides in a debris disc.

Accretion and diffusion in the DAZ white dwarf GALEX J1931+0117