Kappa Ursae Majoris

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Kappa Ursae Majoris
Kappa Ursae Majoris is located in 100x100
Kappa Ursae Majoris
Location of κ Ursae Majoris (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension  09h 03m 37.52762s[1]
Declination +47° 09′ 23.4890″[1]
Apparent magnitude (V) 3.56 (4.16 + 4.54)[2]
Spectral type A0 IV-V + A0 V[3]
Proper motion (μ) RA: −36.19[1] mas/yr
Dec.: −55.40[1] mas/yr
Parallax (π)9.10 ± 0.50[1] mas
Distance360 ± 20 ly
(110 ± 6 pc)
Absolute magnitude (MV)−1.63[4]
Period (P)13,007.2±9.7 d
Semi-major axis (a)0.18194 ± 0.00025
Eccentricity (e)0.5584±0.0015
Inclination (i)109.410±0.066°
Longitude of the node (Ω)105.641±0.080°
Periastron epoch (T)50404 ± 12
Argument of periastron (ω)
Other designations
Alkaphrah, κ UMa, 12 Ursae Majoris, BD+47° 1633, FK5 341, GC 12503, HD 77327, HIP 44471, HR 3594, SAO 42661, PPM 50987, CCDM J09036+4709AB, WDS J09036+4709AB[6]
Database references

Kappa Ursae Majoris (κ Ursae Majoris, abbreviated Kap UMa, κ UMa) is a binary star in the constellation of Ursa Major. With a combined apparent magnitude of +3.60,[7] the system is approximately 358 light-years from Earth.

The two components are designated Kappa Ursae Majoris A (also named Alkaphrah[8]) and B.


κ Ursae Majoris (Latinised to Kappa Ursae Majoris) is the system's Bayer designation. The designations of the two components as Kappa Ursae Majoris A and B derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[9]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[10] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[11] It approved the name Alkaphrah for the component Kappa Ursae Majoris A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[8]

In Chinese, 三台 (Sān Tái), meaning Three Steps, refers to an asterism consisting of Kappa Ursae Majoris, Iota Ursae Majoris, Lambda Ursae Majoris, Mu Ursae Majoris, Nu Ursae Majoris and Xi Ursae Majoris. Consequently, Kappa Ursae Majoris itself is known as 上台二 (Shàng Tái èr, English: Star of Second Upper Step).[12]


Both components of the binary star are white A-type main sequence dwarfs. They have apparent magnitudes of +4.2 and +4.5.[13] The orbital period of the binary is 35.6 years (13,007.2 days), and the two stars are separated by 0.18 arcseconds.[14]


  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:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  3. ^ Edwards, T. W. (April 1976), "MK classification for visual binary components", Astronomical Journal, 81: 245–249, Bibcode:1976AJ.....81..245E, doi:10.1086/111879
  4. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  5. ^ Hartkopf, W. I.; et al. (June 30, 2006), Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, retrieved 2017-06-02.
  6. ^ "CCDM J09036+4709AB -- Double or multiple star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-03-26
  7. ^ Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  8. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  9. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  10. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  11. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  12. ^ (in Chinese) (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 21 日
  13. ^ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  14. ^ Muterspaugh, Matthew W.; et al. (December 2010), "The Phases Differential Astrometry Data Archive. II. Updated Binary Star Orbits and a Long Period Eclipsing Binary", The Astronomical Journal, 140 (6): 1623–1630, arXiv:1010.4043, Bibcode:2010AJ....140.1623M, doi:10.1088/0004-6256/140/6/1623