Omega Ursae Majoris

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Omega Ursae Majoris
Diagram showing star positions and boundaries of the Ursa Major constellation and its surroundings
Cercle rouge 100%.svg

Location of ω Ursae Majoris (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Ursa Major
Right ascension 10h 53m 58.74035s[1]
Declination +43° 11′ 23.8483″[1]
Apparent magnitude (V) 4.61[2]
Spectral type A1VsSi:[3] or A0 IV−V[4]
U−B color index −0.11[2]
B−V color index −0.04[2]
Radial velocity (Rv) −18.70±0.80[5] km/s
Proper motion (μ) RA: +42.97[1] mas/yr
Dec.: −23.62[1] mas/yr
Parallax (π) 13.24 ± 0.50[1] mas
Distance 246 ± 9 ly
(76 ± 3 pc)
Absolute magnitude (MV) +0.86[6]
Period (P) 15.8307 d
Eccentricity (e) 0.31
Periastron epoch (T) 2435185.246 JD
Argument of periastron (ω)
Semi-amplitude (K1)
22.2 km/s
Radius 2.5[8] R
Luminosity 76[9] L
Surface gravity (log g) 3.88[4] cgs
Temperature 9,647[9] K
Rotational velocity (v sin i) 47[10] km/s
Age 325[6] Myr
Other designations
ω UMa, 45 Ursae Majoris, BD+43° 2058, FK5 2870, HD 94334, HIP 53295, HR 4248, SAO 43512.[11]
Database references

Omega Ursae Majoris (Omega UMa, ω Ursae Majoris, ω UMa) is the Bayer designation for a binary star star system in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye with an apparent visual magnitude of 4.61.[2] Based upon an annual parallax shift of 13.24 mas,[1] it is roughly 246 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.11 due to interstellar dust.[6]

This is a single-lined spectroscopic binary star system with an orbital period of 15.8 days and an eccentricity of 0.31.[7] The primary member, component A, is an A-type main sequence star with a stellar classification of A1VsSi:.[3] The stellar spectrum has the appearance of a hot Am star, showing overabundances of many iron-peak and heavier elements, but an underabundance of helium.[12] In particular, it has an abnormal abundance of silicon.[13]


In Chinese, 天牢 (Tiān Láo), meaning Celestial Prison, refers to an asterism consisting of ω Ursae Majoris, 57 Ursae Majoris, 47 Ursae Majoris, 58 Ursae Majoris, 49 Ursae Majoris and 56 Ursae Majoris. Consequently, ω Ursae Majoris itself is known as 天牢一 (Tiān Láo yī, English: the First Star of Celestial Prison.).[14]


  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:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819. 
  4. ^ a b Adelman, S. J. (2005), "The physical properties of normal a stars", Proceedings of the International Astronomical Union, 2004: 1−11, doi:10.1017/S1743921304004314. 
  5. ^ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048Freely accessible, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61. 
  6. ^ a b c Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694−706, arXiv:1606.09028Freely accessible, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035. 
  7. ^ a b Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573Freely accessible, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213. 
  8. ^ Pasinetti-Fracassini, L. E.; et al. (February 2001), "Catalog of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (3rd ed.), 367: 521−524, arXiv:astro-ph/0012289Freely accessible, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451. 
  9. ^ 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:1208.2037Freely accessible, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x. 
  10. ^ Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785Freely accessible, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224. 
  11. ^ "ome UMa -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-02-22. 
  12. ^ Caliskan, Hulya; Adelman, Saul J. (June 1997), "Elemental abundance analyses with DAO spectrograms - XVII. The superficially normal early A stars 2 Lyncis, omicron Ursa Majoris and phiAquilae", Monthly Notices of the Royal Astronomical Society, 288 (2): 501−511, Bibcode:1997MNRAS.288..501C, doi:10.1093/mnras/288.2.501. 
  13. ^ Renson, P.; Manfroid, J. (May 2009), "Catalogue of Ap, HgMn and Am stars", Astronomy and Astrophysics, 498 (3): 961–966, Bibcode:2009A&A...498..961R, doi:10.1051/0004-6361/200810788. 
  14. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 21 日