Iota Orionis

Iota Orionis

Iota Orionis A/B

Hatsya identified in a Stellarium screenshot.
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]
Radial velocity (Rv) 21.5[4] 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
Eccentricity (e) 0.764
Periastron epoch (T) 2,450,072.80 HJD
ι Ori A
Surface gravity (log g) 3.73[3] cgs
Temperature 32,500[3] K
Metallicity [Fe/H] +0.10[5] dex
Rotational velocity (v sin i) 122[6] km/s
Age 4.0–5.5[3] Myr
ι Ori B
Surface gravity (log g) 3.78[3] cgs
Temperature 27,000[3] K
Age 9.4 ± 1.5[3] Myr
Other designations
Na’ir al Saif, Hatsya, Hatysa in Becvar, 44 Orionis, BD-06 1241, FK5 209, HD 37043, HIP 26241, HR 1899, SAO 132323.

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,[2] making it the eighth brightest member of Orion. It is the brightest star in an asterism known as Orion's sword. Iota Orionis has the traditional names Hatsya or Hatysa[7][8] and in Arabic, Na’ir al Saif, which means simply "the Bright One of the Sword."[9] 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 binary is composed of a stellar class O9 III star (blue giant) and a class B0.8 III/IV star, with the secondary being 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]


  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,  
  2. ^ a b c d Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series 34: 1–49.  
  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,  
  4. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, retrieved 2009-09-10 
  5. ^ 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,  
  6. ^ Uesugi, Akira; Fukuda, Ichiro (1970), "Catalogue of rotational velocities of the stars", Contributions from the Institute of Astrophysics and Kwasan Observatory (University of Kyoto),  
  7. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern Star Names. Sky Publishing. p. 62.   Kunitzsch traces the name to Becvar's Atlas Coeli (1951), where it appeared as "Hatysa", but was unable to find an older source.
  8. ^ Bakich, Michael E. (1995), The Cambridge Guide to the Constellations, Cambridge University Press, p. 118,  
  9. ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 317 

External links

  • Iota Orionis by Dr. Jim Kaler.
  • David Darling's encyclopedia entry