10 Scorpii

ω2 Scorpii
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Scorpius
Right ascension  16h 07m 24.32818s[1]
Declination −20° 52′ 07.5518″[1]
Apparent magnitude (V) +4.320[2]
Spectral type G6/8III[3]
U−B color index +0.494[2]
B−V color index +0.850[2]
Radial velocity (Rv)−5.4[4] km/s
Proper motion (μ) RA: +44.81[1] mas/yr
Dec.: −45.42[1] mas/yr
Parallax (π)11.22 ± 0.32[1] mas
Distance291 ± 8 ly
(89 ± 3 pc)
Absolute magnitude (MV)−0.62[5]
Mass3.27[5] M
Radius15.6[6] R
Luminosity141[7] L
Surface gravity (log g)2.62±0.11[8] cgs
Temperature5,363±42[8] K
Metallicity [Fe/H]+0.03±0.05[8] dex
Age282[5] Myr
Other designations
Jabhat al Akrab,[citation needed] ω2 Sco, 10 Scorpii, BD−20° 4408, HD 144608, HIP 78990, HR 5997, SAO 184135.[9]
Database references

ω2 Scorpii, Latinised as Omega2 Scorpii, is a suspected[10] variable star in the zodiac constellation of Scorpius. A component of the visual double star ω Scorpii, it is bright enough to be seen with the naked eye having an apparent visual magnitude of +4.320.[2] The distance to this star, as determined using parallax measurements,[1] is around 291 light years. The visual magnitude of this star is reduced by 0.38 because of extinction from interstellar dust.[5]

It is 0.05 degree north of the ecliptic, so can be occulted by the moon and planets.

This is a G-type giant star with a stellar classification of G6/8III.[3] With an estimated age of 282 million years,[5] it is an evolved, thin disk star that is currently on the red horizontal branch.[11] The interferometry-measured angular diameter of this star is 1.63 ± 0.10 mas,[12] which, at its estimated distance, equates to a physical radius of nearly 16 times the radius of the Sun.[6] It has 3.27 times the mass of the Sun,[5] and radiates 141 times the Sun's luminosity[7] The effective temperature of the star's outer atmosphere is 5,363 K.[8]


In the Cook Islands, a traditional story is told of twins who flee their parents into the sky and become the pair of stars Omega2 and Omega1 Scorpii. The girl, who is called Piri-ere-ua "Inseparable", keeps tight hold of her brother, who is not named.[13] (The IAU used a version of this story from Tahiti to name Mu2 Scorpii.)


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. ^ a b c d Kozok, J. R. (September 1985), "Photometric observations of emission B-stars in the southern Milky Way", Astronomy and Astrophysics Supplement Series, 61: 387–405, Bibcode:1985A&AS...61..387K.
  3. ^ a b Houk, N.; Smith-Moore, M. (1988), Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Declinations -26°.0 to -12°.0, 4, Bibcode:1988mcts.book.....H.
  4. ^ Wilson, R. E. (1953), General Catalogue of Stellar Radial Velocities, Carnegie Institute of Washington D.C., Bibcode:1953GCRV..C......0W.
  5. ^ a b c d e f Takeda, Yoichi; et al. (August 2008), "Stellar Parameters and Elemental Abundances of Late-G Giants", Publications of the Astronomical Society of Japan, 60 (4): 781–802, arXiv:0805.2434, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781.
  6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1.. The radius (R*) is given by:
  7. ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  8. ^ a b c d Prugniel, P.; et al. (2011), "The atmospheric parameters and spectral interpolator for the MILES stars", Astronomy & Astrophysics, 531: A165, arXiv:1104.4952, Bibcode:2011A&A...531A.165P, doi:10.1051/0004-6361/201116769.
  9. ^ "* ome02 Sco". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-09-25.
  10. ^ Sterken, C. (January 1977), "uvby Photometry of the Suspected Variable omega2 Sco", Information Bulletin on Variable Stars, 1230: 1, Bibcode:1977IBVS.1230....1S.
  11. ^ Afşar, M.; et al. (July 2012), "Chemical Compositions of Thin-disk, High-metallicity Red Horizontal-branch Field Stars", The Astronomical Journal, 144 (1): 20, arXiv:1205.3659, Bibcode:2012AJ....144...20A, doi:10.1088/0004-6256/144/1/20, 20.
  12. ^ Richichi, A.; Percheron, I. (May 2002), "CHARM: A Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 386: 492–503, Bibcode:2002A&A...386..492R, CiteSeerX, doi:10.1051/0004-6361:20020236.
  13. ^ Johannes Carl Andersen (1931) Myths and Legends of the Polynesians. 1995 Dover reprint, p.399–400.

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