Plate 7: Three O8–B0 Supergiants

Star Index

Plate 7: Three O8–B0 Supergiants

Three sections from spectrograms having scales of 63 A/mm are shown. The O II features near λλ4349 and 4416 are well marked in ε Ori (B0 Ia) and are considerably weaker in HR 7589 (O9.5 Iab); on the other hand, the O III blend at 3755–60 increases in strength from B0 la to O8 If. The ratio N III 4379 : He I 4387 is also sensitive to spectral type. Since N III passes through maximum intensity between B0 la and O8 If, we consider the ratio O II : O III to be the fundamental discriminant for spectral type for O8–B0 supergiants.

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