The star, 3 Sco, is an excellent example of a helium-weak B-type star. The hydrogen lines of this star clearly place it intermediate in spectral type to the B3 V and the B5 V standards, whereas the strength of the helium lines suggests a spectral type of B8. The Ca II K-line is very weak, and similar in strength to the K-line in B8 stars. The color of this star is consistent with the hydrogen-line type of B4, but not with the Helium-line type. In addition, the star shows a relatively strong C II line at 4267 Å, (compare with the same line in the B3 V standard), again confirming the hotter type. Hence, the spectral type is denoted: kB8 hB4 HeB8 V C II, and we conclude that this star shows a marked helium deficiency.
Helium-strong and helium-weak B-type stars are not mutually exclusive. A number of these stars are spectrum variables. One star, a Cen, varies, on a time scale of a few days between a helium-weak and a helium-strong state.
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