Iota Orionis (ι Orionis, abbreviated ι Ori) is a multiple star system in the equatorial constellation 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 1980 open cluster. From parallax measurements, it is located at a distance of roughly 2,300 light-years (710 parsecs) from the Sun.
The system has three visible components designated Iota Orionis A, B and C. Iota Orionis A is itself a massive spectroscopic binary, with components Iota Orionis Aa (officially named Hatysa /hɑːˈtiːsə/) and Ab.
Epoch J2000 Equinox J2000
|Right ascension||05h 35m 25.98191s|
|Declination||–05° 54′ 35.6435″|
|Apparent magnitude (V)||2.77|
|ι Orionis A|
|Spectral type||O9 III + B0.8 III/IV|
|U−B color index||–1.08|
|B−V color index||–0.24|
|ι Orionis B|
|Spectral type||B8 III|
|ι Orionis A|
|Radial velocity (Rv)||21.5 km/s|
|Proper motion (μ)|| RA: +1.42 mas/yr |
Dec.: –0.46 mas/yr
|Parallax (π)||1.40 ± 0.22 mas|
|Distance||approx. 2,300 ly |
(approx. 700 pc)
|Primary||ι Orionis Aa|
|Companion||ι Orionis Ab|
|Period (P)||29.1338 days|
|Semi-major axis (a)||132 R☉|
|Periastron epoch (T)||2,450,072.80 HJD|
|ι Ori Aa|
|Surface gravity (log g)||3.73 cgs|
|Metallicity [Fe/H]||+0.10 dex|
|Rotational velocity (v sin i)||122 km/s|
|ι Ori Ab|
|Surface gravity (log g)||3.78 cgs|
|Age||9.4 ± 1.5 Myr|
|ι Ori B|
|Surface gravity (log g)||4.0 cgs|
|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|
|ι Ori B|
|ι Ori C|
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 Aa 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).
The system has the traditional name Nair al Saif, from the Arabic نير السيف nayyir as-sayf "the Bright One of the Sword", though this is little used. 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.
In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. 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.
Iota Orionis has a parallax of 1.40±0.22 mas in the Hipparcos new reduction, indicating a distance around 700 pc. The previous published Hipparcos parallax was 2.46±0.77 mas, suggesting a closer distance. Gaia Data Release 2 has individual parallaxes for the two fainter components of the Iota Orionis star system of 2.3839±0.0810 mas and 2.5321±0.0484 mas, indicating distances of 419 pc and 395 pc respectively, with margins of error of just a few parsecs. There is little doubt that all three stars are at the same distance.
Iota Orionis is generally assumed to be associated with the open cluster NGC 1980, which is at a distance of around 400 pc. However, they may not lie at exactly the same distance and Iota Orionis may have a complex history involving stellar encounters and runaway stars. NGC 1980 contains few bright stars other than Iota Orionis. Only eighteen other stars are considered members in a survey down to 14th magnitude, most of them around 9th magnitude but including the 5th magnitude stars HR 1886 and 1887.
Iota Orionis is dominated by Iota Orionis A whose two components are a stellar class O9 III star (blue giant) and a class B0.8 III/IV star about 2 magnitudes fainter. The combined spectral type has long been accepted as O9 III and it was listed as a standard star for that type. The collision of the stellar winds from this pair makes the system a strong X-ray source. Oddly, the two objects of this system appear to have different ages, with the secondary being about double the age of the primary. In combination with the high eccentricity (e=0.764) of their 29-day orbit, this suggests that the binary system was created through a capture, rather than by being formed together and undergoing a mass transfer. This capture may have occurred, for example, through an encounter between two binary systems, with one star being donated from each binary and two runaway stars being ejected.
The primary component of Iota Orionis A is a class O giant star with a mass of about 23 M☉. It has a surface temperature of 32,500 K and radius of 8.3 R☉, resulting in a bolometric luminosity of 68,000 L☉. It is calculated to be around nine million years old. The secondary star of the spectroscopic binary pair is a class B giant or subgiant with a mass of about 13 M☉. It has a temperature of 27,000 K and radius of 5.4 R☉, resulting in it radiating over 8,000 times as much energy as the sun.
Iota Orionis B is a B8 giant at 11" (approximately 5,000 AU) which has been shown to be variable, and likely to be a young stellar object. It is also a helium-weak chemically peculiar star. The fainter Iota Orionis C is an A0 star at 49".
AE Aurigae (abbreviated as AE Aur) is a runaway star in the constellation Auriga; it lights the Flaming Star Nebula.Mu Columbae
Mu Columbae (μ Col, μ Columbae) is a star in the constellation of Columba. It is one of the few O-class stars that are visible to the unaided eye. The star is known to lie approximately 1,300 light years from the Solar System (with an error margin of a few hundred light years).
This is a relatively fast rotating star that completes a full revolution approximately every 1.5 days. (Compare this to the Sun, which at only 22 percent of this star's diameter rotates only once every 25.4 days.) This rate of rotation is fairly typical for stars of this class.
Based on measurements of proper motion and radial velocity, astronomers know that this star and AE Aurigae are moving away from each other at a relative velocity of over 200 km/s. Their common point of origin intersects with Iota Orionis in the Trapezium cluster, some two and half million years in the past. The most likely scenario that could have created these runaway stars is a collision between two binary star systems, with the stars being ejected along different trajectories radial to the point of intersection.NGC 1980
NGC 1980 (also known as OCL 529, Collinder 72 and The Lost Jewel of Orion) is a young open cluster associated with an emission nebula in the constellation Orion. It was discovered by William Herschel on 31 January 1786. Its apparent size is 14 × 14 arc minutes and it is located around the star Iota Orionis on the southern tip of the Orion constellation.Herschel made his first observation of the cluster which was called WH V 31 on 31 January 1786, but he possibly observed it during his studies of double stars on 20 September 1783.O-type main-sequence star
An O-type main-sequence star (O V) is a main-sequence (core hydrogen-burning) star of spectral type O and luminosity class V. These stars have between 15 and 90 times the mass of the Sun and surface temperatures between 30,000 and 50,000 K. They are between 40,000 and 1,000,000 times as luminous as the Sun.O-type star
An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvins (K). Stars of this type have strong absorption lines of ionised helium, strong lines of other ionised elements, and hydrogen and neutral helium lines weaker than spectral type B.
Stars of this type are particularly rare; only 0.00002% (1 in 5,000,000) to 0.00005% (1 in 2,000,000) of all stars are O-type, but because they are very bright they can be seen at great distances and four of the 90 brightest stars as seen from Earth are O type. Due to their high mass, O-type stars end their lives rather quickly in violent supernova explosions, resulting in black holes or neutron stars. Most of these stars are young massive main sequence, giant, or supergiant stars, but the central stars of planetary nebulae, old low-mass stars near the end of their lives, also usually have O spectra.
O-type stars are typically located in regions of active star formation, such as the spiral arms of a spiral galaxy or a pair of galaxies undergoing collision and merger (such as the Antennae Galaxies). These stars illuminate any surrounding material and are largely responsible for the distinct coloration of a galaxy's arms. Furthermore, O-type stars often occur in multiple star systems, where their evolution is more difficult to predict due to mass transfer and the possibility of component stars exploding as supernovae at different times.Orion's Sword
Orion's Sword is an astronomical asterism in the constellation Orion. It comprises three stars (42 Orionis, Theta Orionis, and Iota Orionis) and M42, the Orion Nebula, which together are thought to resemble a sword or a scabbard. This group is situated under the prominent asterism, Orion's Belt, where it points in a southerly direction. Origins behind Orion's Sword are based in mostly Greco-Roman tradition, though this group of stars is referenced as a weapon in multiple cultural contexts (see below).Orion (constellation)
Orion is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous and recognizable constellations in the night sky. It was named after Orion, a hunter in Greek mythology. Its brightest stars are the supergiants: blue-white Rigel (Beta Orionis) and red Betelgeuse (Alpha Orionis).Upsilon Orionis
Upsilon Orionis (υ Ori, υ Orionis) is a star in the constellation Orion. It has the traditional name Thabit or Tabit (ﺛﺎﺑﺖ, Arabic for "the endurer"), a name shared with pi3 Orionis. It is a blue-white main sequence star of apparent magnitude 4.62 located over 3000 light-years distant from the Solar System. It is a suspected Beta Cephei variable.
Stars of Orion