12. B9

The line He I 4026 is weaker relative to K than in class B8. He I 4471 is considerably fainter than Mg II 4481.

TABLE 10
STANDARDS AT B9

Star	MKK	a		m	HD
Crv......	B9 V	12:24	-15°58'	3.1	A0
Lyr......	B9 III	18:55	+32 33	3.3	A0p
a Peg......	B9 V	22:59	+14 40	2.6	A0

The luminosity classification is based on the appearance of the wings of the H lines.

Plate 19. Main Sequence B8 - A2

High resolution image