Iota Orionis (ι Orionis, abbreviated ι Ori) is a multiple star system in the equatorialconstellation of Orion the hunter. It is the eighth-brightest member of Orion with an apparent visual magnitude of 2.77 and also the brightest member of the asterism known as Orion’s Sword. It is a member of the NGC 1980open cluster. From parallax measurements, it is located at a distance of roughly 1,340 light-years (412 parsecs) from the Sun.

ι Orionis

Location of ι Ori (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Orion
Right ascension	05h 35m 25.98191s[1]
Declination	–05° 54′ 35.6435″[1]
Apparent magnitude (V)	2.77[2]
Characteristics
ι Orionis A
Spectral type	O9 III + B0.8 III/IV[3] + B2:IV:[4]
U−B color index	–1.08[2]
B−V color index	–0.24[2]
ι Orionis B
Spectral type	B8 III[5]
Variable type	Orion[6]
Astrometry
ι Orionis A
Radial velocity(Rv)	21.5[7] km/s
Proper motion(μ)	RA: +1.42[1] mas/yr Dec.: –0.46[1] mas/yr
Parallax(π)	1.40 ± 0.22[1] mas
Distance	412+14 −13[4] pc
Orbit[3][8]
Primary	ι Orionis Aa1
Companion	ι Orionis Aa2
Period(P)	29.1338 days
Semi-major axis(a)	132 R☉
Eccentricity(e)	0.764
Inclination(i)	~60°
Periastronepoch(T)	2,450,072.80 HJD
Details
ι Ori Aa1
Mass	23.1[8] M☉
Radius	8.3[8] R☉
Luminosity	68,000[8] L☉
Surface gravity(log g)	3.73[3] cgs
Temperature	32,500[3] K
Metallicity [Fe/H]	+0.10[9] dex
Rotational velocity(v sin i)	122[10] km/s
Age	4.0–5.5[3] Myr
ι Ori Aa2
Mass	13.1[8] M☉
Radius	5.4[8] R☉
Luminosity	8,630[8] L☉
Surface gravity(log g)	3.78[3] cgs
Temperature	27,000[3] K
Age	9.4 ± 1.5[3] Myr
ι Ori B
Mass	5.12[11] M☉
Surface gravity(log g)	4.0[9] cgs
Temperature	18,000[9] K
Age	~3[9] Myr
Other designations
Hatysa, ι Orionis, Na’ir al Saif, Hatsya, BD−06°1241, FK5 209, SAO 132323, ADS 4193, WDS J05354-0555
ι Ori A: 44 Orionis, HD 37043, HIP 26241, HR 1899, 2MASS J05352597-0554357
ι Ori B: V2451 Ori, 2MASS J05352645-0554445
ι Ori C: 2MASS J05352920-0554471
Database references
SIMBAD	ι Ori
	ι Ori B
	ι Ori C

The system has three visible components designated Iota Orionis A, B and C. Iota Orionis A has also been resolved using speckle interferometry and is also a massive spectroscopic binary, with components Iota Orionis Aa1 (officially named Hatysa/hɑːˈtiːsə/), Aa2, and Ab.

. . . Iota Orionis . . .

ι Orionis (Latinised to Iota Orionis) is the system’s Bayer designation. The designations of the three constituents as Iota Orionis A, B and C, and those of A’s components – Iota Orionis Aa1, Aa2, and Ab – derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[12]

The system has the traditional name Nair al Saif, from the Arabic نيرالسيفnayyir as-sayf “the Bright One of the Sword”, though this is little used.[13][14][15] Since Bečvář‘s 1951 Atlas Coeli, it has borne the proper name Hatysa. Kunitzsch was unable to find an older source for the latter name.[16]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[17] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[18] It approved the name Hatysa for the component Iota Orionis Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[19]

Iota Orionis B is a variable star and in 2011 it was given the variable star designation V2451 Orionis.[6]

. . . Iota Orionis . . .

. . . Iota Orionis . . .