2. O9.5

At class O9.5 the line at 4200 is intermediate in intensity between O9 and B0. He I 4541 is weaker than in class O9.

Plate 4. Supergiants O9.5 - A0

High resolution image

TABLE 2
STANDARDS AT O9.5

Star	MKK	a		m	HD	Notes
9 Cam...	O9.5 I	04:44	+66° 10'	4.4	B0
Ori....	O9.5 III	05:26	-00  22	2.5	B0
Ori....	O9.5 V	05:33	-02  39	3.8	B0
Ori....	O9.5 III	05:35	-02  00	2.1	B0
Oph...	O9.5 V	16:31	-10  22	2.7	B0	1
19 Cep..	O9.5 I	22:02	+61  48	5.2	Oe5
NOTES
1. The He I lines are exceedingly broad - considerably broader than in such Bnn stars as UMa and Gas. The lines are intermediate in width between UMa and Per. The interstellar K line appears to be abnormally strong for the spectroscopic luminosity. The line He II 4686 is strong on low-dispersion plates taken especially to minimize the effect of the broad lines. The spectroscopic luminosity is similar to that of Ori.

The absolute-magnitude differences are shown by the ratios 4068: 4089, 4119: 4144, 4387: 4516, and 4650: 4686.

Plate 5. Luminosity Effects at O9

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Plate 6. Luminosity Effects at O9.5

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