Improved Stark-Profile Calculations for the He ii Lines at 256, 304, 1085, 1216, 1640, 3203, and 4686 Å

Abstract

The frequency distributions of the He ii lines at 256, 304, 1085, 1216, 1640, 3203, and 4686 Å, broadened by the local fields of both ions and electrons in a plasma, are calculated in the classical-path approximation. The calculations for the electron broadening are based on an impact theory which accounts for perturbations to both upper and lower levels of the radiating ion. The theory allows (approximately) for the level splitting caused by the fields of the (perturbing) ions, finite duration of the collisions, screening of the electron fields, and includes (approximately) the effects of inelastic collisions. The effect of perturbations by singly charged ions is calculated in the quasistatic linear Stark-effect approximation using Hooper's microfield distribution functions. Comparison to previous calculations shows fair agreement with some increase in linewidth. Comparison with experimental results is less conclusive. Fair agreement is found with some results while others reveal a discrepancy of as much as a factor of 2 in the line wings.