Theta1 Orionis B
Theta1 Orionis B (θ1 Orionis B), also known as BM Orionis, is a multiple star system containing at least five members. It is also one of the main stars of the Trapezium Cluster, with the others being A, C, and D. The primary is an eclipsing variable and one of the youngest known eclipsing binary systems.
θ1 Orionis B and nearby stars in the Trapezium Cluster | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 35m 16.134s |
| Declination | −05° 23′ 6.78″ |
| Apparent magnitude (V) | 7.90 (- 7.98) - 8.65 |
| Characteristics | |
| Spectral type | B1V |
| Variable type | Algol |
| Astrometry | |
| Radial velocity (Rv) | 26 km/s |
| Proper motion (μ) | RA: +1.280 mas/yr Dec.: +1.278 mas/yr |
| Parallax (π) | 2.6548 ± 0.0424 mas |
| Distance | 1,230 ± 20 ly (377 ± 6 pc) |
| Absolute magnitude (MV) | −0.80 |
| Orbit | |
| Period (P) | 6.471 days |
| Semi-amplitude (K1) (primary) | 52.8 km/s |
| Semi-amplitude (K2) (secondary) | 171 km/s |
| Details | |
| B1 | |
| Mass | 6 M☉ |
| Radius | 3 R☉ |
| Luminosity | 776 L☉ |
| Temperature | 19,320 K |
| Rotational velocity (v sin i) | 170 km/s |
| B5 | |
| Mass | 2 M☉ |
| Radius | 8.4 R☉ |
| Luminosity | 80 L☉ |
| Surface gravity (log g) | 3.0 cgs |
| Temperature | 5.740 K |
| Rotational velocity (v sin i) | 60 km/s |
| B2 | |
| Mass | 3 M☉ |
| B3 | |
| Mass | 2.5 M☉ |
| B4 | |
| Mass | 0.2 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
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