Helium lines of sdB stars. The rest wavelengths of the ⁴He (solid) and ³He lines (dotted) are plotted as vertical lines. The rest wavelengths of the ³He lines have been taken from Hartoog & Cowley (1979). The stars are highly enriched in ³He, but also show a component of ⁴He. For comparison, the He lines of SB 815 are plotted in the lowest panel. This star does not show line shifts due to enrichment of ³He.