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Table 6
Spectral type criteria at O8.5–B0 based on specific line-strength ratios (Sota et al. 2011).
| Spectral | He II/He I (a) | Si III/He II (b) |
|---|---|---|
| type | λ4542/λ4388 | λ4553/λ4542 |
| λ4200/λ4144 | ||
| O8.5 | ≥ | N/A |
| O9 | = | ≪ |
| O9.5 | ≤ | < |
| O9.7 | < | ≤ to ≥ |
| B0 | ≪ | ≪ |
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