Theta2 Orionis
 The three components of θ2 Orionis, plus nearby stars Credit: Ian Nartowicz (derived from ESA/Hubble image) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Orion |
| A | |
| Right ascension | 05h 35m 22.90115s |
| Declination | −05° 24′ 57.8207″ |
| Apparent magnitude (V) | 5.02 |
| B | |
| Right ascension | 05h 35m 26.4018s |
| Declination | −05° 25′ 00.720″ |
| Apparent magnitude (V) | 6.380 |
| C | |
| Right ascension | 05h 35m 31.436s |
| Declination | −05° 25′ 16.40″ |
| Apparent magnitude (V) | 8.18 |
| Characteristics | |
| Spectral type | O9.5IVp + B0.7V + B5V |
| Astrometry | |
| Radial velocity (Rv) | 35.6 km/s |
| Proper motion (μ) |
RA: 2.29 mas/yr Dec.: 0.96 mas/yr |
| Parallax (π) | 2.11 ± 0.41mas |
| Distance | approx. 1,500 ly (approx. 470 pc) |
| Absolute magnitude (MV) | −4.3 + −2.60 + −0.6 |
| Details | |
| A | |
| Mass | 39 M☉ |
| Luminosity | 107,000 L☉ |
| Temperature | 34,900 K |
| Rotational velocity (v sin i) | 133 km/s |
| B | |
| Mass | 14.8 M☉ |
| Radius | 4.3 R☉ |
| Luminosity | 12,300 L☉ |
| Surface gravity (log g) | 4.30 cgs |
| Temperature | 29,300 K |
| Rotational velocity (v sin i) | 33 km/s |
| Age | <2 Myr |
| C | |
| Mass | 4.86 M☉ |
| Luminosity | 616 L☉ |
| Temperature | 13,800 K |
| Rotational velocity (v sin i) | 78 km/s |
| Age | <1 Myr |
| Other designations | |
| A: 43 Ori, HR 1897, BD−05°1319, HD 37041, SAO 132321, HIP 26235, CCDM 05353-0524E | |
| B: BD−05°1320, HD 37042, SAO 132322, CCDM 05353-0524F | |
| C: V361 Ori, BD−05°1326, HD 37062, SAO 132329, S 490A, CCDM 05353-0524G | |
| Database references | |
| SIMBAD | A data |
| SIMBAD | B data |
| SIMBAD | C data |
Theta2 Orionis (θ2 Ori) is a multiple star system in the constellation Orion. It is a few arc minutes from its more famous neighbour the Trapezium Cluster, also known as θ1 Orionis.
θ2 Orionis consists of three stars in a line, each about an arc-minute from the next. In addition to the well-known three stars, the Washington Double Star Catalog confusingly lists a component D which is actually θ1 Orionis C.
There is one other star brighter than 10th magnitude in the region. V1073 Orionis is a B9.5 Orion variable that forms an equilateral triangle with θ2 Ori B and C.
Bizarrely, θ2 Orionis C has a second entry in the Washington Double Star Catalog under the name S490. The companion is 10th magnitude and actually lies between θ2 Ori B and V1073 Ori.
θ1 Orionis, the well known Trapezium cluster, is only 2 arc minutes away from θ2 Orionis A. Despite the names, θ2 Orionis A is marginally brighter than the brightest star in the Trapezium. The Catalog of Components of Double and Multiple Stars includes the stars of θ1 and θ2 Ori within the same system of 13 components.
There are dozens of much fainter stars in the same field, many of them pre-main-sequence stars still forming from the Orion Molecular Cloud Complex.
The primary component A appears as a 5th magnitude O class subgiant over 100,000 times as luminous as the sun. The spectral type suggests it is evolving away from the main sequence, although it is thought to be less than 2 million years old. The spectral peculiarities may be related to close companions or could be caused by the extreme youth of the star.
The 6th magnitude component B is an early B main sequence star nearly 30,000 K and over 10,000 times the luminosity of the sun.
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