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Phecda

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(Redirected fromΓ UMa)
"Phad" redirects here. For scroll painting style, seePhad painting.
Phecda
Location of Phecda (circled)
Observation data
EpochJ2000EquinoxJ2000
Constellation Ursa Major
Right ascension 11h53m49.84732s[1]
Declination +53° 41′ 41.1350″[1]
Apparent magnitude(V) 2.438[2]
Characteristics
Spectral type A0 Ve + K2 V[3]
U−Bcolor index +0.008[2]
B−Vcolor 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 ± 0.40mas[1]
Distance83.2 ± 0.8ly
(25.5 ± 0.3pc)
Absolute magnitude(MV)0.4[5]
Orbit[5]
Period(P)20.5 ± 1yr
Semi-major axis(a)0.460″
Eccentricity(e)0.3 ± 0.3
Inclination(i)51 ± 15°
Longitude of the node(Ω)6 ± 61°
Periastronepoch(T)B 1984.0 ± 2.0
Argument of periastron(ω)
(secondary)		185 ± 37°
Details[6]
γ UMa A
Mass2.412+0.053
−0.060M☉
Radius3.385 (equatorial)
2.186 (polar)R☉
Luminosity44.57+3.39
−3.61L☉
Surface gravity(logg)3.79[7]cgs
Temperature6,751 (equatorial)
10,520 (polar)K
Rotational velocity(vsini)184.5+32.6
−35.6km/s
Age333+43
−83Myr
γ UMa B
Mass0.79[3]M☉
Luminosity0.397[3]L☉
Temperature4,780[3]K
Other designations
Phad, Phecda, Phekda, Phegda, Phekha, Phacd, Fekda,[8]γ Ursae Majoris, γ UMa, Gamma UMa, 64 Ursae Majoris,BD+54 1475,FK5447,GC16268,HD103287,HIP58001,HR4554,PPM33292,SAO28179.[9]
Database references
SIMBADdata

Phecda/ˈfɛkdə/,also calledGamma Ursae Majoris(γ Ursae Majoris,abbreviatedGamma UMa,γ UMa),[10][11]is astarin theconstellationofUrsa Major.Since 1943, thespectrumof this star has served as one of the stable anchor points by which other stars are classified.[12]Based uponparallaxmeasurements with theHipparcosastrometry satellite,[13][14]it is located at distance of around 83.2light-years(25.5parsecs) from theSun.[1]

It is more familiar to most observers in thenorthern hemisphereas the lower-left star forming the bowl of theBig Dipper,together withAlpha Ursae Majoris(Dubhe, upper-right),Beta Ursae Majoris(Merak, lower-right) andDelta Ursae Majoris(Megrez, upper-left). Along with four other stars in this well-knownasterism,Phecda forms a loose association of stars known as theUrsa Major moving group.[7]Like the other stars in the group, it is amain sequencestar, as the Sun is, although somewhat hotter, brighter and larger.

Phecda is located in relatively close physical proximity to the prominentMizar–Alcorstar 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 starBeta Ursae Majorisis separated from Gamma Ursae Majoris by 11.0 ly (3.4 pc).[15]

Nomenclature

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γ Ursae Majoris(LatinisedtoGamma Ursae Majoris) is the star'sBayer designation.

It bore the traditional namesPhecdaorPhad,derived from theArabicphraseفخذ الدبfakhth al-dubb('thigh of the bear').[16]In 2016, theInternational Astronomical Unionorganized aWorking Group on Star Names(WGSN)[17]to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[18]included a table of the first two batches of names approved by the WGSN, which includedPhecdafor this star.

To theHindusthis star was known asPulastya,one of theseven rishis.[8]

InChinese,Bắc đấu(Běi Dǒu), meaningNorthern Dipper,refers to an asterism equivalent to the Big Dipper. Consequently, theChinese namefor Gamma Ursae Majoris itself isBắc đấu tam(Běi Dǒu sān,English:the Third Star of Northern Dipper) andThiên cơ(Tiān Jī,English:Star of Celestial Shining Pearl).[19]

Properties

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Phecda is anAe star,which is surrounded by an envelope of gas that is addingemission linesto thespectrumof the star;[20]hence the 'e' suffix in thestellar classificationof A0 Ve.[15]It is 2.4 times more massive than the Sun and is 333 million years old. It rotates rapidly with arotational velocityof 386 km/s at itsequator,which causes it to have an oblate shape. The equatorial radius measures 3.39R☉,while the polar radius measures 2.19R☉.Theeffective temperaturevaries as well, from 6,750 K in the equator to 10,520 K in the poles.[6]

Phecda is also anastrometric binary:the companion star regularly perturbs the Ae-type primary star, causing the primary to wobble around thebarycenter.From this, anorbital periodof 20.5 years has been calculated.[5]The secondary star is aK-type main-sequence starthat is 0.79 times as massive as the Sun, and with a surface temperature of4,780 K.[3]

References

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  1. ^abcdefvan 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,S2CID18759600
  2. ^abcOja, 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
  3. ^abcdeEggl, 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.S2CID73534476.
  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,35(35), Astronomisches Rechen-Institut Heidelberg: 1,Bibcode:1999VeARI..35....1W
  5. ^abcGontcharov, 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.S2CID119252073.
  6. ^abJones, Jeremy; White, R. J.; Boyajian, T.; Schaefer, G.; Baines, E.; Ireland, M.; Patience, J.; Brummelaar, T. ten; McAlister, H.; Ridgway, S. T.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Goldfinger, P. J. (2015-10-28). "The Ages of A-Stars I: Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group".The Astrophysical Journal.813(1): 58.arXiv:1508.05643.doi:10.1088/0004-637X/813/1/58.ISSN1538-4357.
  7. ^abKing, 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. ^abAllen, Richard Hinckley (1899),"Star-names and their meanings",New York,G. E. Stechert,Bibcode:1899sntm.book.....A
  9. ^"PHECDA -- Emission-line Star",SIMBAD,Centre de Données astronomiques de Strasbourg,retrieved2011-12-29
  10. ^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.ISBN978-1-931559-44-7.
  11. ^"IAU Catalog of Star Names".Retrieved28 July2016.
  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,archived fromthe originalon 2019-06-25,retrieved2012-02-04
  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,Astronomers' Universe, Heidelberg:Springer-Verlag,Bibcode:2010mhgs.book.....P,doi:10.1007/978-3-642-11602-5,ISBN978-3-642-11601-8
  15. ^abShaya, 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,S2CID119226823
  16. ^Garfinkle, Robert A. (1997),Star-Hopping: Your Visa to Viewing the Universe,Cambridge University Press,p. 118,ISBN0-521-59889-3
  17. ^"IAU Working Group on Star Names (WGSN)".Retrieved22 May2016.
  18. ^"Bulletin of the IAU Working Group on Star Names, No. 1"(PDF).Retrieved28 July2016.
  19. ^(in Chinese)AEEA (Activities of Exhibition and Education in Astronomy) thiên văn giáo dục tư tấn võng 2006 niên 6 nguyệt 15 nhật
  20. ^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
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