Gamma Ursae Majoris

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Gamma Ursae Majoris
Gamma Ursae Majoris is located in 100x100
Gamma Ursae Majoris

Location of γ Ursae Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 11h 53m 49.84732s[1]
Declination +53° 41′ 41.1350″[1]
Apparent magnitude (V) +2.438[2]
Spectral type A0 Ve[3]
U−B color index +0.008[2]
B−V color index –0.013[2]
Radial velocity (Rv) −12.6[4] km/s
Proper motion (μ) RA: +107.68[1] mas/yr
Dec.: +11.01[1] mas/yr
Parallax (π) 39.21 ± 0.40[1] mas
Distance 83.2 ± 0.8 ly
(25.5 ± 0.3 pc)
Mass 2.62[3] M
Radius 3.04 ± 0.08[5] R
Surface gravity (log g) 3.79[6] cgs
Temperature 9,355[6] K
Rotational velocity (v sin i) 178[7] km/s
Age 0.3[8] Gyr
Other designations
Phad, Phecda, Phekda, Phegda, Phekha, Phacd, Fekda,[9] γ Ursae Majoris, γ UMa, Gamma UMa, 64 Ursae Majoris, BD+54 1475, FK5 447, GC 16268, HD 103287, HIP 58001, HR 4554, PPM 33292, SAO 28179.[10]
Database references

Gamma Ursae Majoris (γ Ursae Majoris, abbreviated Gamma UMa, γ UMa), also named Phecda,[11] is a star in the constellation of Ursa Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[12] Based upon parallax measurements with the Hipparcos astrometry satellite,[13][14] it is located at distance of around 83.2 light-years (25.5 parsecs) from the Sun.[1]

It is more familiar to most observers in the northern hemisphere as the lower-left star forming the bowl of the Big Dipper, together with Alpha Ursae Majoris (Dubhe, upper-right), Beta Ursae Majoris (Merak, lower-right) and Delta Ursae Majoris (Megrez, upper-left). Along with four other stars in this well-known asterism, Phecda forms a loose association of stars known as the Ursa Major moving group.[6] Like the other stars in the group, it is a main sequence star not unlike the Sun, although somewhat hotter, brighter and larger.

Gamma Ursae Majoris is an Ae star, which is surrounded by an envelope of gas that is adding emission lines to the spectrum of the star;[15] hence the 'e' suffix in the stellar classification of A0 Ve.[3] It has 2.6[3] times the mass of the Sun, three times the Sun's radius,[5] and an effective temperature of 9,355 K in its outer atmosphere.[6] This star is rotating rapidly, with a projected rotational velocity of 178 km s−1.[7] The estimated angular diameter of this star is about 0.92 mas.[16] It has an estimated age of 300 million years.[8]

Phecda is located in relatively close physical proximity to the prominent Mizar-Alcor star system. The two are separated by an estimated distance of 8.55 ly (2.62 pc); much closer than the two are from the Sun. The star Beta Ursae Majoris is separated from Gamma UMa by 11.0 ly (3.4 pc).[3]


γ Ursae Majoris (Latinised to Gamma Ursae Majoris) is the star's Bayer designation.

It bore the traditional names Phecda or Phad, derived from the Arabic phrase فخذ الدب fakhð ad-dubb 'thigh of the bear'.[17] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[19] included a table of the first two batches of names approved by the WGSN; which included Phecda for this star.

To the Hindus this star was known as Pulastya, one of the Seven Rishis.[9]

In Chinese, 北斗 (Běi Dǒu), meaning Northern Dipper, refers to an asterism consisting of Gamma Ursae Majoris, Alpha Ursae Majoris, Beta Ursae Majoris, Delta Ursae Majoris, Epsilon Ursae Majoris, Zeta Ursae Majoris and Eta Ursae Majoris. Consequently, Gamma Ursae Majoris itself is known as 北斗三 (Běi Dǒu sān, English: the Third Star of Northern Dipper) and 天璣 (Tiān Jī, English: Star of Celestial Shining Pearl).[20]

See also[edit]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c Oja, T., "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–4 
  3. ^ a b c d e Shaya, Ed J.; Olling, Rob P. (January 2011), "Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue", The Astrophysical Journal Supplement, 192 (1): 2, arXiv:1007.0425free to read, Bibcode:2011ApJS..192....2S, doi:10.1088/0067-0049/192/1/2 
  4. ^ Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35), Bibcode:1999VeARI..35....1W 
  5. ^ a b Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal, 129 (3): 1642–1662, arXiv:astro-ph/0412542free to read, Bibcode:2005AJ....129.1642F, doi:10.1086/427855 
  6. ^ a b c d King, Jeremy R.; et al. (April 2003), "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group", The Astronomical Journal, 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241 
  7. ^ a b Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785free to read, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224 
  8. ^ a b Su, K. Y. L.; et al. (December 2006), "Debris Disk Evolution around A Stars", The Astrophysical Journal, 653 (1): 675–689, arXiv:astro-ph/0608563free to read, Bibcode:2006ApJ...653..675S, doi:10.1086/508649 
  9. ^ a b Allen, Richard Hinckley (1899), "Star-names and their meanings", New York, G. E. Stechert, 
  10. ^ "PHECDA -- Emission-line Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-29 
  11. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  12. ^ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society, 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04 
  13. ^ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; et al. (July 1997), "The Hipparcos Catalogue", Astronomy and Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P 
  14. ^ Perryman, Michael (2010), "The Making of History's Greatest Star Map", The Making of History's Greatest Star Map:, Astronomers’ Universe, Heidelberg: Springer-Verlag,, doi:10.1007/978-3-642-11602-5, ISBN 978-3-642-11601-8 
  15. ^ Jaschek, C.; Andrillat, Y. (June 1998), "AE and A type shell stars", Astronomy and Astrophysics Supplement, 130 (3): 507–512, Bibcode:1998A&AS..130..507J, doi:10.1051/aas:1998101 
  16. ^ Nordgren, Tyler E.; et al. (December 1999), "Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer", The Astronomical Journal, 118 (6): 3032–3038, Bibcode:1999AJ....118.3032N, doi:10.1086/301114 
  17. ^ Garfinkle, Robert A. (1997), Star-Hopping: Your Visa to Viewing the Universe, Cambridge University Press, p. 118, ISBN 0-521-59889-3 
  18. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  19. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. 
  20. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日