Iota Orionis

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ι Orionis
Orion constellation map.svg
Red circle.svg

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]
Spectral type O9 III + B0.8 III/IV[3]
U−B color index –1.08[2]
B−V color index –0.24[2]
Variable type (B) Orion[4]
Radial velocity (Rv) 21.5[5] 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 approx. 2,300 ly
(approx. 700 pc)
Period (P) 29.1338 days
Semi-major axis (a) 132 R
Eccentricity (e) 0.764
Inclination (i) ~60°
Periastron epoch (T) 2,450,072.80 HJD
ι Ori Aa
Mass 23.1[6] M
Radius 8.3[6] R
Luminosity 68,000[6] L
Surface gravity (log g) 3.73[3] cgs
Temperature 32,500[3] K
Metallicity [Fe/H] +0.10[7] dex
Rotational velocity (v sin i) 122[8] km/s
Age 4.0–5.5[3] Myr
ι Ori Ab
Mass 13.1[6] M
Radius 5.4[6] R
Luminosity 8,630[6] L
Surface gravity (log g) 3.78[3] cgs
Temperature 27,000[3] K
Age 9.4 ± 1.5[3] Myr
ι Ori B
Surface gravity (log g) 4.0[9] cgs
Temperature 18,000[9] K
Age ~3[9] Myr
Other designations
ι Orionis, Na’ir al Saif, Hatsya, Hatysa, 44 Orionis, BD−06°1241, FK5 209, HD 37043, HIP 26241, HR 1899, SAO 132323, ADS 4193, WDS J05354-0555
A: ι Ori A, 2MASS J05352597-0554357
B: ι Ori B, V2451 Ori, 2MASS J05352645-0554445
C: ι Ori C, 2MASS J05352920-0554471
Database references
ι Orionis is the bright star to the right of the Orion Nebula

Iota Orionis (ι Ori, ι Orionis) is a star in the equatorial constellation of Orion the hunter. The apparent visual magnitude of Iota Orionis is 2.77, making it the eighth-brightest member of Orion.

Iota Orionis is the brightest star in an asterism known as Orion's sword. It has the traditional names Hatsya or Hatysa[10][11] and in Arabic, Na’ir al Saif, which means simply "the Bright One of the Sword."[12] From parallax measurements, it is located at a distance of roughly 1,330 light-years (410 parsecs) from Earth.[1]

Iota Orionis is a quadruple system dominated by a massive spectroscopic binary with an eccentric (e=0.764), 29-day orbit. The two components of ι Ori A are a stellar class O9 III star (blue giant) and a class B0.8 III/IV star about 2 magnitudes fainter.[3] 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 of their 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.[3]

ι Ori has a B8 giant companion at 11" (approximately 5,000 AU[9]) which has been shown to be variable, and likely to be a young stellar object.[13] There is also a fainter A0 star at 49" catalogued as ι Ori C.[14]

NGC 1980 is an open cluster containing a few bright stars including ι 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.[15]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series. 34: 1–49. Bibcode:1978A&AS...34....1N. 
  3. ^ a b c d e f g h i j Bagnuolo, William G., Jr.; et al. (June 2001), "ι Orionis-Evidence for a Capture Origin Binary", The Astrophysical Journal, 554 (1): 362–367, Bibcode:2001ApJ...554..362B, doi:10.1086/321367 
  4. ^ Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2011). "The 80th Name-List of Variable Stars. Part I - RA 0h to 6h". Information Bulletin on Variable Stars. 5969: 1. Bibcode:2011IBVS.5969....1K. 
  5. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., "The Revision of the General Catalogue of Radial Velocities", Determination of Radial Velocities and their Applications, University of Toronto: International Astronomical Union, 30: 57, Bibcode:1967IAUS...30...57E 
  6. ^ a b c d e f g Marchenko, Sergey V.; Rauw, Gregor; Antokhina, Eleonora A.; Antokhin, Igor I.; Ballereau, Dominique; Chauville, Jacques; Corcoran, Michael F.; Costero, Rafael; Echevarria, Juan; Eversberg, Thomas; Gayley, Ken G.; Koenigsberger, Gloria; Miroshnichenko, Anatoly S.; Moffat, Anthony F. J.; Morrell, Nidia I.; Morrison, Nancy D.; Mulliss, Christopher L.; Pittard, Julian M.; Stevens, Ian R.; Vreux, Jean-Marie; Zorec, Jean (2000). "Coordinated monitoring of the eccentric O-star binary Iota Orionis: Optical spectroscopy and photometry". Monthly Notices of the Royal Astronomical Society. 317 (2): 333. Bibcode:2000MNRAS.317..333M. doi:10.1046/j.1365-8711.2000.03542.x. 
  7. ^ Conti, P. S.; Loonen, J. P. (October 1970), "Coarse analysis of the helium weak B star Iota Ori B", Astronomy and Astrophysics, 8: 197–203, Bibcode:1970A&A.....8..197C 
  8. ^ Uesugi, Akira; Fukuda, Ichiro (1970), "Catalogue of rotational velocities of the stars", Contributions from the Institute of Astrophysics and Kwasan Observatory, University of Kyoto, 
  9. ^ a b c d Conti, P. S.; Loonen, J. P. (1970). "Coarse analysis of the helium weak B star Iota Ori B". Astronomy and Astrophysics. 8: 197. Bibcode:1970A&A.....8..197C. 
  10. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern Star Names. Sky Publishing. p. 62. ISBN 1931559449.  Kunitzsch traces the name to Becvar's Atlas Coeli (1951), where it appeared as "Hatysa", but was unable to find an older source.
  11. ^ Bakich, Michael E. (1995), The Cambridge Guide to the Constellations, Cambridge University Press, p. 118, ISBN 0521449219 
  12. ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 317 
  13. ^ Abt, Helmut A. (2008). "Visual Multiples. IX. MK Spectral Types". The Astrophysical Journal Supplement Series. 176: 216–217. Bibcode:2008ApJS..176..216A. doi:10.1086/525529. 
  14. ^ Parenago, P. P. (1954). "Untersuchung der Sterne im Gebiet des Orion-Nebels. Tabelle III: Katalog der genauen Positionen. (Bestimmung von photographischen Beobachtungen)". Publ. Astr. Inst. Sternberg. 25: 393. Bibcode:1954TrSht..25....1P. 
  15. ^ Kharchenko, N. V.; Piskunov, A. E.; Röser, S.; Schilbach, E.; Scholz, R.-D. (2004). "Astrophysical supplements to the ASCC-2.5. II. Membership probabilities in 520 Galactic open cluster sky areas". Astronomische Nachrichten. 325 (9): 740. Bibcode:2004AN....325..740K. doi:10.1002/asna.200410256. 

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