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2. O9.5

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

Plate 4. Supergiants O9.5 - A0
Plate 4
High resolution image

TABLE 2
STANDARDS AT O9.5

Star MKK a delta m HD Notes

9 Cam... O9.5 I 04:44 +66° 10' 4.4 B0
delta Ori.... O9.5 III 05:26 -00  22 2.5 B0
sigma Ori.... O9.5 V 05:33 -02  39 3.8 B0
zeta Ori.... O9.5 III 05:35 -02  00 2.1 B0
zeta 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 eta UMa and gamma Gas. The lines are intermediate in width between eta UMa and phi 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 sigma Ori.

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

Plate 5. Luminosity Effects at O9
Plate 5
High resolution image

Plate 6. Luminosity Effects at O9.5
Plate 6
High resolution image

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