2 Results and discussion

For the consideration of the influence of charged particle-impacts on spectral lines (Stark broadening), the semiclassical perturbation formalism has been used, which, as well as the corresponding computer code (Sahal-Bréchot 1969a,b), have been updated and improved several times (Sahal-Bréchot 1974; Fleurier et al. 1977, Dimitrijevic & Sahal-Bréchot 1984; Dimitrijevic et al. 1991; Dimitrijevic & Sahal-Bréchot 1996b). Short reviews of the method of calculations, with the discussion of improvements and validity criteria, have been published several times as e.g. in Dimitrijevic & Sahal-Bréchot (1996c) and Dimitrijevic (1996). The atomic energy levels needed for calculations, have been taken from Isler et al. (1993) for O VII, and from Martin & Zalubas (1980) for Mg XI. 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 14 O VII and 18 Mg XI multiplets are shown in Tables 1 and 2 (accessible only in electronic form), for perturber densities 10¹⁷-10²³ cm^-3 and temperatures T= 100000 - 2000000 K for O VII and for perturber densities 10¹⁸-10²⁴ cm^-3 and temperatures T= 500000- 5000000 K for Mg XI. The complete set of data is given for the perturber density of 10¹⁹cm^-3 in both cases, while for lower densities, only data needed for better interpolation are given. Stark broadening parameters for densities lower than tabulated, or for transitions not tabulated for perturber densities lower than 10¹⁹ cm^-3, are proportional to the perturber density. Moreover, we present in Tables 1 and 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 and 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.

One may conclude from Tables 1 and 2, that for multicharged ion lines like O VII and Mg XI lines, ion broadening is not always a small correction to the linewidth, as it is e.g. for singly- and doubly-charged ions, but it is often comparable or even dominant for temperatures of the order of 1000000 K or larger. One should note as well that shifts due to He III- and proton-impacts become dominant in comparison to electron - impact ones.

The presented results may be useful for a number of problems in stellar and laboratory plasma research, modeling and diagnostic. They are also of interest for investigation and modeling of fusion and laser-produced plasmas, as well as for the investigation and modeling of soft X-ray lasers. Such results also have an interest for further development and refinements of the Stark broadening theory for

multicharged ion line shapes and different theoretical considerations, particularly for the investigation of systematic trends of Stark broadening parameters 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.