2 Results and discussion

For the consideration of Stark broadening of K VIII and K IX spectral lines and the determination of the corresponding broadening parameters (the full line width at half maximum - W and the line shift - d), the semiclassical perturbation formalism has been used. This formalism, as well as the corresponding computer code (Sahal-Bréchot 1969a,b), have been updated and optimized several times (Sahal-Bréchot 1974; Fleurier et al. 1977; Dimitrijevic & Sahal-Bréchot 1984; Dimitrijevic et al. 1991; Dimitrijevic & Sahal-Bréchot 1996b). The calculation procedure, with the discussion of updatings and validity criteria, has been briefly reviewed e.g. in Dimitrijevic & Sahal-Bréchot (1996c) and Dimitrijevic (1996). Atomic energy levels needed for calculations have been taken from Bashkin & Stoner (1978). The oscillator strengths have been calculated within the Coulomb approximation (Bates & Damgaard 1949, and the tables of Oertel & Shomo 1968). For higher levels, the method of Van Regemorter et al. (1979) has been used.

Our results for electron-, proton-, and He III-impact line widths and shifts for 4 K VIII and 30 K IX multiplets are shown in Tables 1 and 2 (accessibles only in electronic form), for K VIII (Table 1) for temperatures from 200000 K up to 3000000 K and perturber densities 10¹⁸ cm^-3 - 10²² cm^-3, and for K IX (Table 2) for temperatures from 200000 K up to 5000000 K and perturber densities 10¹⁸ cm^-3 - 10²² cm^-3.

Stark broadening data for densities lower than for tabulated data, are proportional to the perturber density. Moreover, we present in Tables 1-2 as well, a parameter c (Dimitrijevic & Sahal-Bréchot 1984), which gives an estimate for the maximum perturber density for which the line may be treated as isolated, when it is divided by the corresponding full width at half maximum. For each value given in Tables 1-2, the collision volume (V) multiplied by the perturber density (N) is much less than one and the impact approximation is valid (Sahal-Bréchot 1969a,b). Values for NV > 0.5 are not given and values for $0.1 < NV \le 0.5$ are denoted by an asterisk. When the impact approximation is not valid, the ion broadening contribution may be estimated by using the quasistatic approach (Sahal-Bréchot 1991 or Griem 1974). In the region between where neither of these two approximations is valid, a unified type theory should be used. For example in Barnard et al. (1974), a simple analytical formula for such a case is given. The accuracy of the results obtained decreases when broadening by ion interactions becomes important.

There is no experimental data concerning the Stark broadening of K VIII and K IX spectral lines. It exists however, a prediction for K IX 4s²S- 4p²P$^\circ$ Stark width (Djenize & Labat 1996), obtained with the help of established regularities of the Stark widths along Na isoelectronic sequence. For $T = 500\,000$ K and an electron density of 10¹⁷ cm^-3, Djenize & Labat (1996) obtained for the Stark full width (FWHM) the value of $0.0057\ \pm\ 25\%$ Å, while the present result is 0.0099 Å. We hope that the presented data will be of interest for some problems in stellar and laboratory plasma research, especially for subphotospheric layers consideration, investigation and modeling of fusion and laser-produced plasmas, and of soft X-ray lasers, as well as for the checking and development of the Stark broadening theory for multicharged ion line shapes, as e.g. for investigations of systematic trends along isoelectronic sequences.

Acknowledgements

This work is a part of the project "Astrometrical, Astrodynamical and Astrophysical Investigations", supported by Ministry of Science and Technology of Serbia.