Luminosity sequence for B7. HD 21071 is the primary standard for B7 V, but it is clearly earlier than 16 Tau, and may be classified as B6 V if this spectral subtype is used. The Be nature of η Tau, which led to its rejection as a standard, is evident in the emission infilling of Hβ. The star is also very noticeably more luminous than β Tau. HD 183143, the original B7 Ia standard, may be considered a hypergiant (see Fig. 5.2.5).