4. B0.5

The blend at 4640-4650 is strongest at the red edge and is intermediate in appearance between B0 and B1. Si III 4552 is approximately equal to Si IV 4089. Luminosity differences are shown by the lines of O II near H. They are very strong in the spectrum of the supergiant Cas. The line ratios used for luminosity classification are 3995: 4009, 4119: 4144, 4349: 4387, and 4416: 4387.

TABLE 4
STANDARDS AT B0.5

Star	MKK	a		m	HD
CAs....	B0.5 I	0:27	+62° 23'	4.2	B0
Per......	B0.5 III	3:51	+39 43	3.0	B1
139 Tau..	B0.5 II	5:51	+25 56	4.9	B2
Sco.....	B0.5 IV	15:59	-19 32	2.9	B1

Plate 9. Luminosity Effects at B0.5

High resolution image