Stark Broadening of Neutral Helium Lines in a Plasma

Abstract

The frequency distributions of spectral lines of nonhydrogenic atoms broadened by local Gelds of both electrons and ions in a plasma are calculated in the classical path approximation. The electron collisions are treated by an impact theory which takes into account deviations from adiabaticity. For the ion e6ects, the adiabatic approximation can be used to describe the time-dependent wave functions. The various approximations employed were examined for self-consistency, and an accuracy of about 20% in the resulting line profiles is expected. Good agreement with Wulff's experimental helium line profiles was obtained while there are large deviations from the adiabatic theory, especially for the line shifts. Asymptotic distributions for the line wings are given for astrophysical applications. Here the ion eKects can be as important as the electron effects and lead to large asymmetries, but near the line core electrons usually dominate. Numerical results are tabulated for 24 neutral helium lines with principal quantum numbers up to five.

The rotation of the primary of Algol

“…A stream of circumstellar matter, associated with the mass transfer from the Roche-lobe-filling secondary to the primary, is a possible site for the broadening. Such a scenario, in which the site of the Stark broadening is separate from the photosphere, can account for the asymmetry of the broad wings, whose center appears to (Griem et al 1962 , Table I) and the calculated relative shift, d/w where d and w are the shift and electron impact (half) half-widths, respectively, is consistent with the observed shift and width of the broad-winged component of the line.…”

On the nature of sn stars

“…To improve the modelling of the He I profiles, we used detailed line broadening tables for the line 4471 Å (Barnard et al 1974) and for the lines 4026 Å, 4387 Å, and 4922 Å (Shamey 1969). Most of these profiles have been computed assuming quasistatic broadening by ions and impact broadening by electrons, with the semiclassical broadening theory for overlapping lines of Griem et al (1962). Although these detailed calculations do not include all lines of He I, they do include the line 4026 Å, which clearly displays the sn characteristics (a broad He I line) in all stars of our sample.…”

Neutral helium spectral lines in dense plasmas

“…An appropriate strong electronic collision term for the width of neutral helium, which is also introduced by Griem et al [51], should be added to the width in Eq. (8), and the shift according to Eq.…”

“…A systematic calculation for strong collisions is possible by partial summation of diagrams forming a three-particle T-matrix [57] or by using the close-coupling method [70]. To avoid a perturbative expansion with respect to the interaction, strong collision contributions to the broadening are estimated by a Lorentz-Weisskopf approximation [51,52,69] with the introduction of a cut-off parameter for the q-integration see Eq. (8).…”

“…Note that the influence of electrons and ions can be treated separately due to the difference in mass and mobility. Various approaches have been modified to account these effects [47][48][49][50][51][52]. Helium series were calculated from semiclassical approach by Griem et al [51,52], using a traditional impact approximation for electrons with cut-off procedure, while almost stationary heavy ions are treated in a quasi-static ion approximation due to static microfield.…”