Theta1 Orionis B

For other stars with this Bayer designation, see θ Orionis.
θ1 Orionis B

θ1 Orionis B and nearby stars in the Trapezium Cluster
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 35m 16.134s[1]
Declination −05° 23′ 6.78″[1]
Apparent magnitude (V) 7.90 (- 7.98) - 8.65[2]
Characteristics
Spectral type B1V[3]
Variable type Algol[2]
Astrometry
Radial velocity (Rv)26 km/s
Proper motion (μ) RA: +1.280[1] mas/yr
Dec.: +1.278[1] mas/yr
Parallax (π)2.6548 ± 0.0424 mas[1]
Distance1,230 ± 20 ly
(377 ± 6 pc)
Absolute magnitude (MV)−0.80[4]
Orbit[5]
Period (P)6.471 days
Semi-amplitude (K1)
(primary)		52.8 km/s
Semi-amplitude (K2)
(secondary)		171 km/s
Details
B1
Mass6[5] M☉
Radius3[5] R☉
Luminosity776[4] L☉
Temperature19,320[4] K
Rotational velocity (v sin i)170[6] km/s
B5
Mass2[5] M☉
Radius8.4[6] R☉
Luminosity80[6] L☉
Surface gravity (log g)3.0[6] cgs
Temperature5.740[6] K
Rotational velocity (v sin i)60[6] km/s
B2
Mass3[7] M☉
B3
Mass2.5[7] M☉
B4
Mass0.2[7] M☉
Other designations
41 Orionis B, BM Orionis, HD 37021, HR 1894, TYC 4774-954-1, 2MASS J05351611-0523068
Database references
SIMBADdata

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.

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