On the Stark broadening of Cr II spectral lines in atmospheres of DB white dwarfs Z. Simić 1, M. S. Dimitrijević 1,2, A. Kovačević 3, S. Sahal-Bréchot 2 1 Astronomical Observatory, Volgina 7, Belgrade, Serbia 2 Observatoire de Paris-Meudon, Meudon, France 3 Department for Astronomy, Faculty for Mathematics, Belgrade, Serbia

Data on the Stark broadening of neutral atom and ion lines are of interest not only for laboratory but also for astrophysical plasma research, particularly for stellar spectra synthesis and analysis. Here, we investigated theoretically the influence of collisions with charged particles on heavy metal spectral line profiles for singly charged emitter Cr II in atmospheres of chemically peculiar stars, especially in DB white dwarfs.

SEMICLASSICAL THEORY (Sahal-Bréchot, 1969ab) (Sahal-Bréchot, 1974; 1991; Fleurier et al. 1977; Dimitrijević & Sahal-Bréchot, 1984a;1996; Dimitrijević et al. 1991)

Cr II (Z=24) 3d 5 6 S 5/2 - Adelman & Philip (1996): 7 Sex - SC theory: *7 strongest 4s-4p multiplets N=10 14 cm -3 ; T [2500, ] K Rathore et al. (1984): experimental data for Cr II multiplet 5 (4s 4 D-4p 4 F o ) *Dimitrijević, M.S., Ryabchikova, T., Simić, Z., Popović, L.Č., & Dačić, M., 2007, A&A, 469, resonant 3d 5 -3d 4 4p multiplets N=10 17 cm -3 ; T [ 2500, ] K

Resonant Cr II Å line profile - SYNTH code for a model atmosphere (T eff = 8750 K, log g =4.0) Comparison of the Cr II Å line profile a: without Stark broadening contribition and with this contribution for different Cr abundances log Cr/H : b: Solar one, c: -3.75, d: -3.25, e:

Thermal Doppler and Stark widths for Cr II multiplets 3d 5 4 F-3d 4 4p 4 F o ( Å) and 3d 5 4 F-3d 4 4p 4 P o ( Å), for a DB white dwarfs atmosphere model (Wickramasinghe 1972) with Teff = 15,000 K and log g = 8.0, as a function of the optical depth.

The Cr II lines analyzed here are particularly suitable for such purpose since they have good clean wings where the influence of Stark broadening is the most important.

Thank you for attention!