Omicron Scorpii

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ο Scorpii
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 16h 20m 38.18068s[1]
Declination −24° 10′ 09.5491″[1]
Apparent magnitude (V) +4.57[2]
Spectral type A4II/III[3]
B−V color index 0.5125[2]
Radial velocity (Rv) −8.2[4] km/s
Proper motion (μ) RA: −4.32[1] mas/yr
Dec.: −14.15[1] mas/yr
Parallax (π) 3.71 ± 0.54[1] mas
Distance approx. 900 ly
(approx. 270 pc)
Absolute magnitude (MV) −4.0[2]
Mass 7.9±0.1[3] M
Radius 15[5] R
Luminosity 3,162[2] L
Surface gravity (log g) 2.42[2] cgs
Temperature 8,128[2] K
Rotational velocity (v sin i) 23[6] km/s
Age 39.8±4.9[3] Myr
Other designations
ο Sco, 19 Scorpii, CD−23° 12849, HD 147084, HIP 80079, HR 6081, SAO 184329.[7]

Omicron Scorpii (ο Sco, ο Scorpii) is a star in the zodiac constellation of Scorpius. With an apparent visual magnitude of +4.57,[2] it is visible to the naked eye. Parallax measurements indicate a distance of roughly 900 light years. It is located in the proximity of the Rho Ophiuchi dark cloud.[8]

This is a white A-type bright giant with a stellar classification of A4II/III.[3] It is one of the brighter members of this rare class of stars, making it of interest for study.[8] Omicron Scorpii has about eight times the mass of the Sun, fifteen times the radius,[5] and is roughly 40 million years old.[3] The star is radiating around 3,200 times the luminosity of the Sun from its outer atmosphere at an effective temperature of about 8,128 K.[2] It does not display an infrared excess due to circumstellar dust or a possible infrared-bright companion, but the light from this star is subject to extinction from interstellar dust.[8]

Omicron Scorpii was occasionally mentioned as a possible member of the Upper Scorpius sub-group in the Scorpius-Centaurus OB association during the 20th century.[2] However, it does not appear in more recent membership lists for this group[9] due to its small proper motion and small trigonometric parallax as measured by Hipparcos. This suggests that it is a background star unrelated to Scorpius-Centaurus.


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d e f g h i de Geus, E. J.; et al. (June 1989), "Physical parameters of stars in the Scorpio-Centaurus OB association", Astronomy and Astrophysics, 216 (1-2): 44–61, Bibcode:1989A&A...216...44D. 
  3. ^ a b c d e Tetzlaff, N.; et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x. 
  4. ^ 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, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E. 
  5. ^ a b Pasinetti Fracassini, L. E.; et al. (2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy & Astrophysics, 367: 521–24, arXiv:astro-ph/0012289Freely accessible, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451. 
  6. ^ Royer, F.; et al. (October 2012), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897–911, arXiv:astro-ph/0205255Freely accessible, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943. 
  7. ^ "omi Sco -- Variable Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-09-22. 
  8. ^ a b c Whittet, D. C. B. (February 1988), "On the nature and environment of Omicron Scorpii", Monthly Notices of the Royal Astronomical Society, 230: 473–478, Bibcode:1988MNRAS.230..473W, doi:10.1093/mnras/230.3.473. 
  9. ^ de Zeeuw, P.T.; et al. (1999). "A Hipparcos Census of Nearby OB Associations". Astronomical Journal. 117 (1): 354–399. arXiv:astro-ph/9809227Freely accessible. Bibcode:1999AJ....117..354D. doi:10.1086/300682.