Abstract
Equivalents widths of He II lines in the series n=2,3,4 and 5 are compiled and compared with predictions from plane-parallel, static model atmospheres using a non-LTE theory of line formation. The agreement between observation and prediction for a (50,000,4.0) model atmosphere is good for the upper members of the n=3 and the n=5 series, but the two lines of the n=2 series which are observed and the upper members of the n=4 series (4$Yields$15,4$Yields$17, etc.) are stronger than predicted. Well-determined profiles of lines from the n=3 series indicate v sin i=200 km s$sup -1$. Profiles of the higher members of the n=4 series, however, do not match the predictions, the observed line cores being deeper than predicted. The n=4 level appears to be more overpopulated at moderate depths in the atmosphere than the non-LTE calculations with plane-parallel layers indicate. This may be due to an overlap of the H and He II lines in the even-even series caused by macroturbulent velocities of the hydrogen atoms and helium atoms. (AIP)
Published Version
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