Eta Orionis

η Orionis
Location of η Orionis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 24m 28.61672s[1]
Declination –02° 23′ 49.7311″[1]
Apparent magnitude (V) 3.42[2] (4.50 + 5.90 + 5.65 + 4.95)[3]
Characteristics
Spectral type Aa: B1 V
Ab: B3 V
Ac: B3 V
B: B2 V[3]
U−B color index –0.90[2]
B−V color index −0.17[2]
Variable type Algol[4]
Astrometry
Radial velocity (Rv)+19.8[5] km/s
Proper motion (μ) RA: −0.71[1] mas/yr
Dec.: −3.46[1] mas/yr
Parallax (π)3.34 ± 1.07 mas[1]
Distanceapprox. 1,000 ly
(approx. 300 pc)
Orbit[6]
PrimaryAa
CompanionAb
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[3]
CompanionAc
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
Mass11.0±0.5[6] M☉
Radius6.3±0.6[6] R☉
Temperature26,600[6] K
Rotational velocity (v sin i)20[6] km/s
η Ori Ab
Mass10.6±0.7[6] M☉
Radius5.2±0.4[6] R☉
Temperature26,600[6] K
Rotational velocity (v sin i)130[6] km/s
η Ori Ac
Mass6.78[7] M☉
η Ori B
Mass8.7[7] M☉
Other designations
η Ori, 28 Orionis, BD−02°1235, HD 35411, HIP 25281, HR 1788, SAO 132071[8]
Database references
SIMBADdata

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.

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