Table 1
Indices used to derive the spectral type for stars later than M2.5.
| Name | λ Numerator | λ Denominator | Range | Calibration | Reference |
|
|
|||||
| PC1 | 7030−7050 | 7525−7550 | M3−M9 | −0.06 + 2.95 X | 1, 2, 4 |
| PC2 | 7540−7580 | 7030−7050 | M4−M8 | –0.63 + 3.89 X | 1, 2, 4 |
| R1 | 8025−8130 | 8015−8025 | M2.5−M8 | 2.8078 + 21.085(X − 1.044)−53.025(X − 1.044)2+60.755(X − 1.044) | 3 |
| R2 | 8415−8460 | 8460−8470 | M3−M8 | 2.9091 + 10.503(X − 1.035)−14.105(X − 1.035)2+8.5121(X − 1.035) | 3 |
| R3 | (8125−8130) + (8415−8460) | (8015−8025)+(8460−8470) | M2.5−M8 | 2.8379 + 19.708(X − 1.035) – 47.679(X − 1.035)2 + 52.531(X − 1.035) | 3 |
| TiO 8465 | 8405−8425 | 8455−8475 | M3−M8 | 3.2147 + 8.7311(X − 1.085) − 10.142(X − 1.085)2 + 5.6765(X − 1.085) | 3 |
| VOa | (7350−7370)+(7550−7570) | 7430−7470 | M5−M9 | 5.0705 + 11.226(x − 0.982) + 6.7099(x − 0.982)2 | 3 |
| VOb | (7860−7880)+(8080−8100) | 7960−8000 | M4−M9 | 3.4875 + 29.469(x − 1.017) − 156.53(x − 1.017)2 + 394.28(x − 1.017) − 325.44(x − 1.017)4 | 3 |
Notes. Indices used for spectral typing of mid- and late-M type stars. The wavelengths are given in Å. In the calibration, X represents the index obtained by dividing the numerator and denominator, and the resulting number indicates the M subtype.
Reference. 1 = Kirkpatrick et al. (1995); 2 = Martín et al. (1996); 3 = Riddick et al. (2007). 4 = Sicilia-Aguilar et al. (2008).
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