6. B2

The blend near 4072 is weaker than at B1. Si II 4128-4130 is fainter than in class B3. The luminosity classes were determined from the ratios 3995: 4009, 4121: 4144, 4387: 4552 and from the appearance of the wings of the hydrogen lines. The stars Peg and Cas are located between classes B2 and B3.

NOTES

TABLE 6
STANDARDS AT B2

Star	MKK	a		m	HD	Notes
Peg......	B2.5 IV	0:08	+14°38'	2.9	B2
Cas.....	B2.5 IV	0:31	+53 21	3.7	B3
Ori......	B2 IV	5:19	+ 6 16	1.7	B2
2 Ori.....	B2 I	5:58	+20 8	4.7	B2p
Sco......	B2 IV	15:52	-25 50	3.0	B2
Oph......	B2 V	16:19	-23 13	5.2	B5	1
Oph......	B2 IV	17:15	-24 54	3.4	B3
Sco......	B2 IV	17:26	-37 2	1.7	B2
9 Cep......	B2 I	21:35	+61 38	4.9	B2p	2
12 Lac.....	B2 III	22:37	+39 42	5.2	B2
1. The He I lines are as strong as in other B2 stars and are considerably stronger than at class B5. The H lines are strong and broad; this has been taken to be an effect of low luminosity in a B2 spectrum rather than a reason for classifying the star as B5. The H lines are somewhat weaker than in UMa (B3). All spectral lines are very broad.
2. The star 9 Cep is a pronounced supergiant but spectroscopic evidence ( 3995: 4009, 4387: 4552, intensity of H lines) indicates that it is definitely less luminous than Ori.

The luminosity effects are so well marked at B2 that there is no ambiguity in the location of any of the stars in the five luminosity classes used.

Plate 11. Luminosity Effects at B2

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Plate 12. The Be Stars and Phi Persei

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Plate 13. The Bnn Stars

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Plate 14. P Cygni

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