Copernicus observations of neutral helium lines in early-type stars.

Abstract

Observations of stellar ultraviolet He I lines at 2829, 2945, and 3187 A obtained with the Copernicus Satellite, are compared with LTE and non-LTE calculations. The stars observed cover the range of spectral types O8-B7 and luminosity Classes I-V and were chosen to have relatively low projected rotational velocities. The equivalent widths measured with the two near ultraviolet Copernicus spectrometers (VI and V2) are in satisfactory accord both with each other and with results obtained from balloon flights and the IUE satellite. The model atmosphere calculations use the 'complete linearization procedure' and are similar to those of Auer and Mihalas (1973) but with a different choice of atomic data. For stars of Class II-V the observations and non-LTE calculations for the 2829 and 2945 A lines are in satisfactory agreement but there is an unresolved discrepancy for the 3187 A line. For the Class I supergiants neither LTE nor non-LTE theory reproduces the observations, in common with that found previously for visible triplet lines. In an appendix LTE and non-LTE equivalent widths are tabulated for T-sub-eff = 15,000 to 27,500 K and log 0 = 3 and 4.