We present in this paper the results of a theoretical study of electron impact broadening for several lines of the Ar VII ion. The results have been obtained using our quantum mechanical method and the semiclassical perturbation one. Results are presented for electron density 10¹⁸ cm⁻³ and for electron temperatures ranging from $2\times {10}^4$ to $5\times {10}^5$ K required for plasma modeling. Our results have been compared to other semiclassical ones obtained using different sources of atomic data. A study of the strong collisions contributions to line broadening has been performed. The atomic structure and collision data used for the calculations of line broadening are also calculated by our codes and compared to available theoretical results. The agreement found between the two calculations ensures that our line broadening procedure uses adequate structure and collision data.

Context. This paper provides missing Stark broadening of the Br VI and Kr V-VII lines recently discovered in the ultraviolet spectrum of the hot white dwarf RE 0503–289 and investigates the importance of the Stark broadening mechanism versus the Doppler mechanism in that star. As far as we know, this is the first time that Stark widths of Br VI and Kr V-VII lines have been calculated. Aims. The recent discovery of new lines of Br VI and Kr V-VII encourages us to provide their Stark broadening to enrich the STARK-B database and for use in interpretations of the observed spectra. Methods. We used our quantum mechanical method for calculating electron impact broadening to provide Stark widths. The method starts with an evaluation of the structure and collision parameters using the University College London codes SUPERSTRUCTURE/DISTORTED WAVE/JAJOM, which are adapted to the line broadening calculations. We then used the collision parameters to calculate the line widths using our programs. Results. We provide the missing widths of 35 lines of Br VI and Kr V-VII at different electron temperatures and at density N_e = 10¹⁷ cm⁻³. We find that the Stark broadening mechanism is preponderant compared to the Doppler one for almost all the plasma conditions of the considered DO white dwarf atmospheres.