Analyses of Light Ion Spectra in Stellar Atmospheres.IV. H II in the B Stars

Results of an extensive set of computations of the He I spectrum in B stars, allowing for departures from LTE, using rather complete model atoms, non-LTE model atmospheres, and somewhat improved broadening theory, are presented and discussed. Among the major conclusions we derive are the following: (1) While departures from LTE alter equivalent widths but little in the blue- violet spectral region, their effects are quite large for lines in the visual-red region (e.g., A6678). (2) Very good agreement is obtained in the comparison of our calculated profiles with observed He iline profiles both in the wings and in the cores (except for some triplets at spectral types B0 and B1). (3) Some of the largest effects of departures from LTE occur at the highest and lowest effective temperatures, where the lines are relatively weak. (4) The usually quoted blue-violet singlet/triplet ratio is unaffected by departures from LTE to within the errors of observation. Other line ratios (e.g., A6678/A5876), however, are strongly affected. (5) The systematic wavelength-effect noted by Norris is explained. Good agreement is obtained with most of the conclusions of Johnson and Poland and Poland, though some significant differences arising from non-LTE effects in the model atmospheres are noted. The present results allow analysis for a much wider range of stellar spectral types and luminosity classes with a much higher level of physical consistency than hitherto possible. Subject headings: atmospheres, stellar - early-type stars - line formation