Sigma Orionis
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.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 38m 42.0s |
| Declination | −2° 36′ 00″ |
| Apparent magnitude (V) | A: 4.07 B: 5.27 C: 8.79 D: 6.62 E: 6.66 (6.61 - 6.77) |
| Characteristics | |
| AB | |
| Spectral type | O9.5V + B0.5V |
| U−B color index | −1.02 |
| B−V color index | −0.31 |
| C | |
| Spectral type | A2 V |
| U−B color index | −0.25 |
| B−V color index | −0.02 |
| D | |
| Spectral type | B2 V |
| U−B color index | −0.87 |
| B−V color index | −0.17 |
| E | |
| Spectral type | B2 Vpe |
| U−B color index | −0.84 |
| B−V color index | −0.09 |
| Variable type | SX Ari |
| Astrometry | |
| Radial velocity (Rv) | −29.45 ± 0.45 km/s |
| Parallax (π) | AB: 3.04 ± 8.92 mas D: 6.38 ± 0.90 mas |
| Distance | 387.51 ± 1.32 pc |
| Absolute magnitude (MV) | −3.49 (Aa) −2.90 (Ab) −2.79 (B) |
| Orbit | |
| Primary | Aa |
| Companion | 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° |
| Semi-amplitude (K1) (primary) | 72.03 ± 0.25 km/s |
| Semi-amplitude (K2) (secondary) | 95.53 ± 0.22 km/s |
| Orbit | |
| Primary | A |
| Companion | 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° |
| 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 |
| Details | |
| C | |
| Mass | 2.7 M☉ |
| Details | |
| D | |
| Mass | 6.8 M☉ |
| Surface gravity (log g) | 4.3 cgs |
| Temperature | 21,500 K |
| Rotational velocity (v sin i) | 180 km/s |
| Details | |
| 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 |
| Rotation | 1.190847 days |
| Rotational velocity (v sin i) | 140±10 km/s |
| Age | 0.4-0.9 Myr |
| Other designations | |
| 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 | |
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