Γ_Ursae_Majoris

Phecda

Phecda

Star in the constellation Ursa Major

"Phad" redirects here. For scroll painting style, see Phad painting.

Phecda /ˈfɛkdə/, also called Gamma Ursae Majoris (γ Ursae Majoris, abbreviated Gamma UMa, γ UMa),[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]

Quick Facts Observation data Epoch J2000 Equinox J2000, Constellation ...

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, as the Sun is, 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]

References

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    Oja, T. (1986), "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–4, Bibcode:1986A&AS...65..405O
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    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. S2CID 73534476.
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    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. S2CID 119252073.
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    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
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    Allen, Richard Hinckley (1899), "Star-names and their meanings", New York, G. E. Stechert, Bibcode:1899sntm.book.....A
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    "PHECDA -- Emission-line Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-29
  12. [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. [13]
    "IAU Catalog of Star Names". Retrieved 28 July 2016.
  14. [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, archived from the original on 2019-06-25, retrieved 2012-02-04
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    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
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    Perryman, Michael (2010), 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
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    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, S2CID 119226823
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    "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
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    (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日
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    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. [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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