Eta Orionis
Eta Orionis or Algjebbah, Latinized from η Orionis, is a multiple star in the constellation Orion. It lies a little to the west of Orion's Belt between Delta Orionis and Rigel, being closer to Delta Orionis than to Rigel. It lies at a distance of around 1,000 light-years from Earth and is part of the Orion OB1 association.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 24m 28.61672s |
| Declination | –02° 23′ 49.7311″ |
| Apparent magnitude (V) | 3.42 (4.50 + 5.90 + 5.65 + 4.95) |
| Characteristics | |
| Spectral type | Aa: B1 V Ab: B3 V Ac: B3 V B: B2 V |
| U−B color index | –0.90 |
| B−V color index | −0.17 |
| Variable type | Algol |
| Astrometry | |
| Radial velocity (Rv) | +19.8 km/s |
| Proper motion (μ) | RA: −0.71 mas/yr Dec.: −3.46 mas/yr |
| Parallax (π) | 3.34 ± 1.07 mas |
| Distance | approx. 1,000 ly (approx. 300 pc) |
| Orbit | |
| Primary | Aa |
| Companion | Ab |
| Period (P) | 7.989255±0.000005 days |
| Eccentricity (e) | 0.011±0.0002 |
| Inclination (i) | 85° |
| Semi-amplitude (K1) (primary) | 145.5±0.03 km/s |
| Semi-amplitude (K2) (secondary) | 150±3 km/s |
| Orbit | |
| Companion | Ac |
| Period (P) | 9.442±0.012 yr |
| Semi-major axis (a) | 0.0441±0.0015″ |
| Eccentricity (e) | 0.45±0.02 |
| Inclination (i) | 102.8±1.8° |
| Details | |
| η Ori Aa | |
| Mass | 11.0±0.5 M☉ |
| Radius | 6.3±0.6 R☉ |
| Temperature | 26,600 K |
| Rotational velocity (v sin i) | 20 km/s |
| η Ori Ab | |
| Mass | 10.6±0.7 M☉ |
| Radius | 5.2±0.4 R☉ |
| Temperature | 26,600 K |
| Rotational velocity (v sin i) | 130 km/s |
| η Ori Ac | |
| Mass | 6.78 M☉ |
| η Ori B | |
| Mass | 8.7 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
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