Sigma Orionis
  | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Orion |
| σ Ori AB | |
| Right ascension | 05h 38m 44.765s |
| Declination | −02° 36′ 00.28″ |
| Apparent magnitude (V) | 4.07 + 5.27 |
| σ Ori C | |
| Right ascension | 05h 38m 44.119s |
| Declination | −02° 36′ 06.31″ |
| Apparent magnitude (V) | 8.79 |
| σ Ori D | |
| Right ascension | 05h 38m 45.625s |
| Declination | −02° 35′ 58.89″ |
| Apparent magnitude (V) | 6.62 |
| σ Ori E | |
| Right ascension | 05h 38m 47.205s |
| Declination | −02° 35′ 40.52″ |
| Apparent magnitude (V) | 6.61 - 6.77 |
| Characteristics | |
| σ Ori AB | |
| Spectral type | O9.5V + B0.5V |
| U−B color index | −1.02 |
| B−V color index | −0.31 |
| σ Ori C | |
| Evolutionary stage | main sequence |
| Spectral type | A2 V |
| U−B color index | −0.25 |
| B−V color index | −0.02 |
| σ Ori D | |
| Evolutionary stage | main sequence |
| Spectral type | B2 V |
| U−B color index | −0.87 |
| B−V color index | −0.17 |
| σ Ori E | |
| Evolutionary stage | main sequence |
| Spectral type | B2 Vpe |
| U−B color index | −0.84 |
| B−V color index | −0.09 |
| Variable type | SX Ari |
| Astrometry | |
| σ Ori AB | |
| Radial velocity (Rv) | −29.45±0.45 km/s |
| Parallax (π) | 3.04±8.92 mas |
| Distance | 387.51±1.32 pc |
| Absolute magnitude (MV) | −3.49 (Aa) −2.90 (Ab) −2.79 (B) |
| σ Ori C | |
| Radial velocity (Rv) | 26.91±7.48 km/s |
| Proper motion (μ) | RA: 0.358±0.028 mas/yr Dec.: −1.064±0.027 mas/yr |
| Parallax (π) | 2.4720±0.0293 mas |
| Distance | 1,320 ± 20 ly (405 ± 5 pc) |
| Absolute magnitude (MV) | 1.04 |
| σ Ori D | |
| Proper motion (μ) | RA: 1.618±0.058 mas/yr Dec.: 0.036±0.052 mas/yr |
| Parallax (π) | 2.4744±0.0622 mas |
| Distance | 1,320 ± 30 ly (400 ± 10 pc) |
| Absolute magnitude (MV) | +0.89 |
| σ Ori E | |
| Proper motion (μ) | RA: 1.284±0.063 mas/yr Dec.: −0.205±0.059 mas/yr |
| Parallax (π) | 2.3077±0.0647 mas |
| Distance | 1,410 ± 40 ly (430 ± 10 pc) |
| Absolute magnitude (MV) | 2.12 |
| Orbit | |
| Primary | Aa |
| Name | Ab |
| Period (P) | 143.2002±0.0024 days |
| Semi-major axis (a) | 0.0042860" (~360 R☉) |
| Eccentricity (e) | 0.77896±0.00043 |
| Inclination (i) | ~56.378±0.085° |
| Longitude of the node (Ω) | 6.9° |
| Periastron epoch (T) | 56597.638 |
| Argument of periastron (ω) (secondary) | 199.8° |
| Semi-amplitude (K1) (primary) | 72.03±0.25 km/s |
| Semi-amplitude (K2) (secondary) | 95.53±0.22 km/s |
| Orbit | |
| Primary | A |
| Name | B |
| Period (P) | 159.896±0.005 yr |
| Semi-major axis (a) | 0.2629±0.0022″ |
| Eccentricity (e) | 0.024±0.005 |
| Inclination (i) | 172.1±4.6° |
| Longitude of the node (Ω) | 7.4° |
| Periastron epoch (T) | 1999.207 |
| Argument of periastron (ω) (secondary) | 301.6° |
| Details | |
| σ Ori Aa | |
| Mass | 18 M☉ |
| Radius | 5.6 R☉ |
| Luminosity | 41,700 L☉ |
| Surface gravity (log g) | 4.20 cgs |
| Temperature | 35,000 K |
| Rotational velocity (v sin i) | 135 km/s |
| Age | 0.3 Myr |
| σ Ori Ab | |
| Mass | 13 M☉ |
| Radius | 4.8 R☉ |
| Luminosity | 18,600 L☉ |
| Surface gravity (log g) | 4.20 cgs |
| Temperature | 31,000 K |
| Rotational velocity (v sin i) | 35 km/s |
| Age | 0.9 Myr |
| σ Ori B | |
| Mass | 14 M☉ |
| Radius | 5.0 R☉ |
| Luminosity | 15,800 L☉ |
| Surface gravity (log g) | 4.15 cgs |
| Temperature | 29,000 K |
| Rotational velocity (v sin i) | 250 km/s |
| Age | 1.9 Myr |
| σ Ori C | |
| Mass | 2.7 M☉ |
| Radius | 2.050±0.073 R☉ |
| Luminosity | 38.5±0.08 L☉ |
| Surface gravity (log g) | 4.10±0.04 cgs |
| Temperature | 10,067±7 K |
| Metallicity [Fe/H] | −0.628±0.003 dex |
| Age | 0.251±0.001 Myr |
| σ Ori D | |
| Mass | 6.8 M☉ |
| Radius | 4.471±0.004 R☉ |
| Luminosity | 128.6±0.03 L☉ |
| Surface gravity (log g) | 4.3 cgs |
| Temperature | 21,500 K |
| Metallicity [Fe/H] | 0.485±0.001 dex |
| Rotational velocity (v sin i) | 180 km/s |
| σ Ori E | |
| Mass | 8.30 M☉ |
| Radius | 3.77 R☉ |
| Luminosity | 3,162 L☉ |
| Surface gravity (log g) | 4.2±0.2 cgs |
| Temperature | 22,500 K |
| Metallicity [Fe/H] | 0.144±0.006 dex |
| Rotation | 1.190847 days |
| Rotational velocity (v sin i) | 140±10 km/s |
| Age | 0.4-0.9 Myr |
| Other designations | |
| Sigma Orionis, Sigma Ori, σ Orionis, σ Ori, 48 Orionis, 48 Ori | |
| AB: HD 37468, HR 1931, HIP 26549, SAO 132406, BD−02°1326, 2MASS J05384476-0236001, Mayrit AB | |
| C: 2MASS J05384411-0236062, Mayrit 11238 | |
| D: HIP 26551, 2MASS J05384561-0235588, Mayrit 13084 | |
| E: V1030 Orionis, HR 1932, HD 37479, BD−02°1327, 2MASS J05384719-0235405, Mayrit 41062 | |
| Database references | |
| SIMBAD | σ Ori |
| σ Ori C | |
| σ Ori D | |
| σ Ori E | |
| σ Ori Cluster | |
Sigma Orionis or Sigma Ori (σ Orionis, σ Ori) is a multiple star system in the constellation Orion, consisting of the brightest members of a young open cluster. It is found at the eastern end of the belt, south west of Alnitak and west of the Horsehead Nebula which it partially illuminates. The combined brightness of the component stars is magnitude 3.80.