Omega Ursae Majoris

Omega Ursae Majoris (Omega UMa, ω Ursae Majoris, ω UMa) is the Bayer designation for a binary 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]

Omega Ursae Majoris
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]
Characteristics
Spectral type A1VsSi:[3] or A0 IV−V[4]
U−B color index −0.11[2]
B−V color index −0.04[2]
Astrometry
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
Distance246 ± 9 ly
(76 ± 3 pc)
Absolute magnitude (MV)+0.86[6]
Orbit[7]
Period (P)15.8307 d
Eccentricity (e)0.31
Periastron epoch (T)2435185.246 JD
Argument of periastron (ω)
(secondary)		27.3°
Semi-amplitude (K1)
(primary)		22.2 km/s
Details
Radius2.5[8] R☉
Luminosity76[9] L☉
Surface gravity (log g)3.88[4] cgs
Temperature9,647[9] K
Rotational velocity (v sin i)47[10] km/s
Age325[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
SIMBADdata

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]

Naming

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, the Chinese name for ω Ursae Majoris itself is 天牢一 (Tiān Láo yī, English: the First Star of Celestial Prison.).[14]

References
  1. 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, S2CID 18759600.
  2. 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. 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. Adelman, S. J. (2005), "The physical properties of normal a stars", Proceedings of the International Astronomical Union, 2004: 1–11, Bibcode:2004IAUS..224....1A, 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:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  6. Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694–706, arXiv:1606.09028, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035, S2CID 119108982.
  7. 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): 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088.
  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/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
  9. 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, S2CID 118665352.
  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/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224, S2CID 18475298.
  11. "* ome UMa". SIMBAD. 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
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