Gamma Ursae Majoris

Gamma Ursae Majoris (γ Ursae Majoris, abbreviated Gamma UMa, γ UMa), formally named Phecda /ˈfɛkdə/,[12][13] 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.[14] Based upon parallax measurements with the Hipparcos astrometry satellite,[15][16] it is located at distance of around 83.2 light-years (25.5 parsecs) from the Sun.[1]

"Phad" redirects here. For scroll painting style, see Phad painting.
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]
Characteristics
Spectral type A0 Ve + K2 V[3]
U−B color index +0.008[2]
B−V color index –0.013[2]
Astrometry
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
Distance83.2 ± 0.8 ly
(25.5 ± 0.3 pc)
Absolute magnitude (MV)+0.4[5]
Orbit[5]
Period (P)20.5 ± 1 yr
Semi-major axis (a)0.460″
Eccentricity (e)0.3 ± 0.3
Inclination (i)51 ± 15°
Longitude of the node (Ω)6 ± 61°
Periastron epoch (T)B 1984.0 ± 2.0
Argument of periastron (ω)
(secondary)		185 ± 37°
Details
γ UMa A
Mass2.94[3] M☉
Radius3.04 ± 0.08[6] R☉
Luminosity65.255[3] L☉
Surface gravity (log g)3.79[7] cgs
Temperature9,355[7] K
Rotational velocity (v sin i)178[8] km/s
Age0.3[9] Gyr
γ UMa B
Mass0.79[3] M☉
Luminosity0.397[3] L☉
Temperature4,780[3] K
Other designations
Phad, Phecda, Phekda, Phegda, Phekha, Phacd, Fekda,[10] 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.[11]
Database references
SIMBADdata

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.[7] Like the other stars in the group, it is a main sequence star not unlike the Sun, although somewhat hotter, brighter and larger.

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 Ursae Majoris by 11.0 ly (3.4 pc).[17]

Nomenclature

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 fakhth al-dubb 'thigh of the bear'.[18] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[19] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[20] 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.[10]

In Chinese, 北斗 (Běi Dǒu), meaning Northern Dipper, refers to an asterism equivalent to the Big Dipper. Consequently, the Chinese name for Gamma Ursae Majoris itself is 北斗三 (Běi Dǒu sān, English: the Third Star of Northern Dipper) and 天璣 (Tiān Jī, English: Star of Celestial Shining Pearl).[21]

Properties

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;[22] hence the 'e' suffix in the stellar classification of A0 Ve.[17] It has 2.6[17] times the mass of the Sun, three times the Sun's radius,[6] and an effective temperature of 9,355 K in its outer atmosphere.[7] This star is rotating rapidly, with a projected rotational velocity of 178 km s−1.[8] The estimated angular diameter of this star is about 0.92 mas.[23] It has an estimated age of 300 million years.[9]

Gamma Ursae Majoris is also an astrometric binary: the companion star regularly perturbs the Ae-type primary star, causing the primary to wobble around the barycenter. From this, an orbital period of 20.5 years has been calculated.[5] The secondary star is a K-type main-sequence star that is 0.79 times as massive as the Sun, and with a surface temperature of 4,780 K.[3]

gollark: They should be held to high standards, considering their position.
gollark: It means to make local.
gollark: Assuming these "military police" had higher standards than regular police now, would that still be the case if you scaled that system up to match all the ones they're replacing?
gollark: Members of parliament?
gollark: Whatever the cause actually is, I'm not sure there really is a hugely consistent one.

See also

References
  1. 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. Oja, T., "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–4
  3. Eggl, S.; Pilat-Lohinger, E.; Funk, B.; Georgakarakos, N.; Haghighipour, N. (2012). "Circumstellar habitable zones of binary-star systems in the solar neighbourhood". Monthly Notices of the Royal Astronomical Society. 428 (4): 3104. arXiv:1210.5411. Bibcode:2013MNRAS.428.3104E. doi:10.1093/mnras/sts257.
  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): 1, Bibcode:1999VeARI..35....1W
  5. Gontcharov, G.A.; Kiyaeva, O.V. (2010). "Photocentric orbits from a direct combination of ground-based astrometry with Hipparcos II. Preliminary orbits for six astrometric binaries". New Astronomy. 15 (3): 324–331. arXiv:1606.08182. Bibcode:2010NewA...15..324G. doi:10.1016/j.newast.2009.09.006.
  6. 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/0412542, Bibcode:2005AJ....129.1642F, doi:10.1086/427855
  7. 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
  8. 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/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224
  9. Su, K. Y. L.; et al. (December 2006), "Debris Disk Evolution around A Stars", The Astrophysical Journal, 653 (1): 675–689, arXiv:astro-ph/0608563, Bibcode:2006ApJ...653..675S, doi:10.1086/508649
  10. Allen, Richard Hinckley (1899), "Star-names and their meanings", New York, G. E. Stechert, Bibcode:1899sntm.book.....A
  11. "PHECDA -- Emission-line Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-29
  12. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  13. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  14. 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
  15. 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
  16. Perryman, Michael (2010), "The Making of History's Greatest Star Map", The Making of History's Greatest Star Map, Astronomers’ Universe, Heidelberg: Springer-Verlag, Bibcode:2010mhgs.book.....P, doi:10.1007/978-3-642-11602-5, ISBN 978-3-642-11601-8
  17. 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:1007.0425, Bibcode:2011ApJS..192....2S, doi:10.1088/0067-0049/192/1/2
  18. Garfinkle, Robert A. (1997), Star-Hopping: Your Visa to Viewing the Universe, Cambridge University Press, p. 118, ISBN 0-521-59889-3
  19. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  20. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  21. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日
  22. 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
  23. 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
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