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Astron. Astrophys. 329, 792-798 (1998)

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1. Introduction

About fifteen to twenty five years ago, a unified quantum theory of spectral line broadening has been developed (Van Regemorter 1969; Tran Minh and Van Regemorter 1972) and applied to the wings of the Lyman- [FORMULA] line of hydrogen atom (Tran Minh et al. 1975; Feautrier et al. 1976; Feautrier and Tran Minh 1977; Tran Minh et al. 1980). The validity of the results were checked by comparison with those of the semiclassical theories of Lisitsa and Sholin (1972), Voslamber (1972) and Caby-Eyraud et al. (1975); but also with the experimental results of Boldt and Cooper (1964) and Fussmann (1975). This formalism was shown to be particularly adapted for the description of line wings. It was then found that simple dipolar semiclassical calculations are valid not too far from the line core, but that quantum theory must be applied in the far wings. Since then, many theoretical works of importance have been carried out on Ly [FORMULA]. One can mention the recent calculations of Stehlé (1994), who has tabulated the profiles of Lyman, Balmer and Paschen lines of hydrogen using a formalism based on the Model Microfield Method. These calculations provide an improvement in the line core, as compared to Vidal et al.(1973), because of the dynamical effects of ions and the simultaneous strong collisions that are taken into account. One can also mention the works of Günter and Könies(1994) and also Könies and Günter (1994) that deal with quantum mechanical electronic widths and shifts of spectral lines (over the full profile) and the electronic asymmetry of Ly [FORMULA], based on the Green's function technique.

Very few applications were made with the quantum unified theory mentioned above because of the numerical difficulties in the far wings. Calculations were carried out only for the plasma conditions of experiments, for comparison. The aim of the present work is to use this formalism to study the density effects on electronic broadening of Ly [FORMULA]. The theory is briefly presented in Sect. 2, followed by the analysis of the density effects in Sect. 3. Sect. 4 deals with the extrapolation method used to describe the contribution of the first angular momenta. The results obtained by this method are close within a good precision to those provided by the semi-empirical method of Feautrier and Tran Minh (1977). In Sect. 5, a comment is made on asymmetry; the contribution of the short range potentials such as quadrupole and polarization potentials is discussed. Last before the conclusion, Sect. 6 is concerned with the comparison of our results with those of Vidal et al.(1973), hereafter referred to as VCS, and their polynomial fit for temperatures varying from 2500 to 40000K [FORMULA] and detunings [FORMULA] below 80Å.

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997