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Castor (star)

Coordinates:Sky map07h34m36s,+31° 53′ 18″
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Castor
Location of Castor (circled)
Observation data
EpochJ2000EquinoxJ2000
Constellation Gemini
Pronunciation /ˈkæstər/[1]
A
Right ascension 07h34m35.863s[2]
Declination +31° 53′ 17.79″[2]
Apparent magnitude(V) 1.93[2]
B
Right ascension 07h34m36.100s[2]
Declination +31° 53′ 18.57″[2]
Apparent magnitude(V) 2.97[2]
C
Right ascension 07h34m37.584s[2]
Declination +31° 53′ 17.8160″[2]
Apparent magnitude(V) 9.83[2]
Characteristics
A
Spectral type A1V + dM1e[3]
B−Vcolor index +0.03[4]
B
Spectral type Am + dM1e[3]
B−Vcolor index +0.04[4]
C
Spectral type dM1e + dM1e[3]
U−Bcolor index +1.04[5]
B−Vcolor index +1.49[5]
Variable type BY Dra[6]
Astrometry
AB
Radial velocity(Rv)5.40[7]km/s
Proper motion(μ)RA:–191.45[8]mas/yr
Dec.:–145.19[8]mas/yr
Parallax(π)64.12 ± 3.75mas[8]
Distance51 ± 3ly
(15.6 ± 0.9pc)
Absolute magnitude(MV)+0.986 / +1.886[4]
C
Radial velocity(Rv)+2.5[9]km/s
Proper motion(μ)RA:–201.490[10]mas/yr
Dec.:–97.104[10]mas/yr
Parallax(π)66.2323 ± 0.0511mas[10]
Distance49.24 ± 0.04ly
(15.10 ± 0.01pc)
Absolute magnitude(MV)+8.950[11]
Details
α Geminorum Aa
Mass2.37[12]M☉
Radius2.089[12]R☉
Surface gravity(logg)4.2[13]cgs
Temperature10,286[14]K
Rotational velocity(vsini)18[15]km/s
Age290[12]Myr
α Geminorum Ba
Mass1.79[12]M☉
Radius1.648[12]R☉
Surface gravity(logg)4.0[13]cgs
Temperature8,842[14]K
Rotational velocity(vsini)33[15]km/s
α Geminorum Ca/Cb (components are identical)
Mass0.5992[11]M☉
Radius0.6191[11]R☉
Luminosity0.0733[11]L☉
Surface gravity(logg)4.6317[11]cgs
Temperature3,820[11]K
Metallicity[Fe/H]~0.0[11]dex
Rotational velocity(vsini)37[11]km/s
Age370[11]Myr
Orbit[12]
Primaryα Geminorum A
Companionα Geminorum B
Period(P)459yr
Semi-major axis(a)6.722″
Eccentricity(e)0.338
Inclination(i)115.1°
Longitude of the node(Ω)41.3°
Periastronepoch(T)2436785
Argument of periastron(ω)
(secondary)		251.84°
Orbit[16]
Primaryα Geminorum Aa
Companionα Geminorum Ab
Period(P)9.2128 days
Eccentricity(e)0.5
Periastronepoch(T)2427543.938
Argument of periastron(ω)
(primary)		266.4°
Semi-amplitude(K1)
(primary)		12.9 km/s
Orbit[16]
Primaryα Geminorum Ba
Companionα Geminorum Bb
Period(P)2.9283 days
Periastronepoch(T)2427501.703
Argument of periastron(ω)
(primary)		94.7°
Semi-amplitude(K1)
(primary)		31.9 km/s
Orbit[16]
Primaryα Geminorum AB
Companionα Geminorum C
Period(P)14,000yr
Orbit[11]
Primaryα Geminorum Ca
Companionα Geminorum Cb
Period(P)0.814 days
Eccentricity(e)0
Inclination(i)86.29 ± 0.10°
Longitude of the node(Ω)7.315°
Semi-amplitude(K1)
(primary)		121.0 km/s
Semi-amplitude(K2)
(secondary)		119.0 km/s
Other designations
Castor,α Gem,66 Geminorum,FK5287,GJ278,HIP36850,SAO60198
A:BD+32°1581A,HD60179,HR2891,PLX1785.00
B:BD+32°1581B,HD60178,HR2890
C:YY Geminorum,BD+32°1582
Database references
SIMBADdata
Castor A
Castor B
Castor C (YY Gem)

Castoris the second-brightest object in thezodiacconstellationofGemini.It has theBayer designationα Geminorum,which isLatinisedtoAlpha Geminorumand abbreviatedAlpha Gemorα Gem.With anapparent visual magnitudeof 1.58, it isone of the brightest starsin thenight sky.Castor appears singular to the naked eye, but it is actually a sextuplestar systemorganized into threebinary pairs.Although it is the 'α' ( Alpha ) member of the constellation, it is fainter than 'β' (beta) Geminorum,Pollux.

Stellar system[edit]

Aa
Period = 9.2128 d
Ab
Separation =3.9″
Ba
Period = 2.9283 d
Bb
Separation =71″
Ca
Period = 0.814 d
Cb

Hierarchy of orbits in the Castor system[17]

Castor is amultiple star systemmade up of six individual stars; there are three visual components, all of which arespectroscopic binaries.Appearing to the naked eye as a single star, Castor was first recorded as adouble starin 1718 byJames Pound,but it may have been resolved into at least two sources of light byCassinias early as 1678. The separation between thebinary systemsCastor A and Castor B has increased from about 2″ (2arcsecondsof angular measurement) in 1970 to about 6″ in 2017.[18][16]These pairs havemagnitudesof 1.9 and 3.0, respectively.

Castor Aa and Ba both have orbits of a few days with a much fainter companion.

Castor C, or YY Geminorum, was discovered to vary in brightness with a regular period. It is aneclipsing binarywith additional variations due to areas of different brightness on the surface of one or both stars, as well as irregular flares.[11]The Castor C components orbit in less than a day. Castor C is believed to be in orbit around Castor AB, but with an extremely long period of several thousand years. It is 73″ distant from the bright components.[16]

The combined apparent magnitude of all six stars is +1.58.

Physical properties[edit]

Castor is 51light-yearsaway from Earth, determined from its large annualparallax.

The two brightest stars are bothA-type main-sequence stars,more massive and brighter than the Sun. The properties of theirred dwarfcompanions are difficult to determine, but are both thought to have less than half themass of the Sun.[16]

Avisual bandlight curvefor YY Geminorum (Castor C), adapted from Butleret al.(2015)[19]

Castor B is anAm star,with particularly strong spectral lines of certain metals.

Castor C is a variable star, classified as aBY Draconistype. BY Draconis variables are cool dwarf stars which vary as they rotate due tostarspotsor other variations in theirphotospheres.The two red dwarfs of Castor C are almost identical, with masses around a halfM☉and luminosities less than 10% of the Sun.[11]

All the red dwarfs in the Castor system have emissions lines in their spectra, and all areflare stars.[13]

Etymology and culture[edit]

α Geminorum(LatinisedtoAlpha Geminorum) is the star system'sBayer designation.

Castor and Pollux are the two "heavenly twin" stars that give the constellation Gemini (meaningtwinsin Latin) its name. The nameCastorrefers specifically toCastor,one of the twin sons ofZeusandLedain Greek and Roman mythology.

The star was annotated by theArabicdescriptionAl Ras al Taum al Muqadim,which translates asthe head of the foremost twin.In the catalogue of stars in theCalendarium of al Achsasi al Mouakket,this star was designatedAoul al Dzira,which was translated intoLatinasPrima Brachii,meaningthe first in the paw.[20]

InChinese,Bắc Hà(Běi Hé), meaningNorth River,refers to an asterism consisting of Castor,Rho Geminorum,andPollux.[21]Consequently, Castor itself is known asBắc Hà nhị(Běi Hé èr,English:the Second Star of North River.)[22]

In 2016, theInternational Astronomical Unionorganized aWorking Group on Star Names(WGSN)[23]to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which includedCastorfor the star α Geminorum Aa.[24]

Castor C also has thevariable-star designationYY Geminorum.

  • The Castor AB pair resolved
    The Castor AB pair resolved
  • Components
    Components
  • Castor is one of the two brightest stars in the constellation of Gemini (top left star).
    Castor is one of the two brightest stars in the constellation of Gemini (top left star).

See also[edit]

References[edit]

  1. ^ Kunitzsch, Paul; Smart, Tim, eds. (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.
  2. ^abcdefghi Fabricius, C.; Høg, E.; Makarov, V.V.; Mason, B.D.; Wycoff, G.L.; Urban, S.E. (March 2002)."The Tycho double star catalogue".Astronomy and Astrophysics.384:180–189.Bibcode:2002A&A...384..180F.doi:10.1051/0004-6361:20011822.
  3. ^abc Pourbaix, D.; Tokovinin, A.A.; Batten, A.H.; Fekel, F.C.; Hartkopf, W.I.; Levato, H.; et al. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits".Astronomy and Astrophysics.424(2): 727–732.arXiv:astro-ph/0406573.Bibcode:2004A&A...424..727P.doi:10.1051/0004-6361:20041213.ISSN0004-6361.S2CID119387088.
  4. ^abc Barrado y Navascues, D. (1998). "The Castor moving group. The age of Fomalhaut and Vega".Astronomy and Astrophysics.339:831–839.arXiv:astro-ph/9905243.Bibcode:1998A&A...339..831B.
  5. ^ab Ducati, J. R. (2002). Ducati, J.R. (ed.). "VizieR Online Data Catalog: Catalogue of stellar photometry in Johnson's 11 color system".Vizier Online Data Catalog.CDS/ADC Collection of Electronic Catalogues.2237.Bibcode:2002yCat.2237....0D.
  6. ^ Samus, N.N.; Durlevich, O.V.; et al. (2009). "VizieR Online Data Catalog: General catalogue of variable stars (Samus+ 2007–2013)".Vizier Online Data Catalog.VizieR On-line Data Catalog: B/GCVS.1:02025.Bibcode:2009yCat....102025S.Originally published in: 2009yCat....102025S
  7. ^ Gontcharov, G.A. (November 2006). "Pulkovo compilation of radial velocities for 35,495 Hipparcos stars in a common system".Astronomy Letters.32(11): 759–771.arXiv:1606.08053.Bibcode:2006AstL...32..759G.doi:10.1134/S1063773706110065.S2CID119231169.
  8. ^abc 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.S2CID18759600.
  9. ^ Wilson, Ralph Elmer (1953). "General Catalogue of Stellar Radial Velocities".Carnegie Institute Washington D.C. Publication.Washington, DC:Carnegie Institution of Washington.Bibcode:1953GCRV..C......0W.
  10. ^abcBrown, A. G. A.;et al. (Gaia collaboration) (August 2018)."GaiaData Release 2: Summary of the contents and survey properties ".Astronomy & Astrophysics.616.A1.arXiv:1804.09365.Bibcode:2018A&A...616A...1G.doi:10.1051/0004-6361/201833051.Gaia DR2 record for this sourceatVizieR.
  11. ^abcdefghijkl Torres, Guillermo; Ribas, Ignasi (2002). "Absolute dimensions of the M-type eclipsing binary YY Geminorum (Castor C): A challenge to evolutionary models in the lower Main Sequence".The Astrophysical Journal.567(2): 1140–1165.arXiv:astro-ph/0111167.Bibcode:2002ApJ...567.1140T.doi:10.1086/338587.ISSN0004-637X.S2CID16780943.
  12. ^abcdef Torres, Guillermo; et al. (2022)."The Orbits and Dynamical Masses of the Castor System".The Astrophysical Journal.941(8): 8.arXiv:2210.16322.Bibcode:2022ApJ...941....8T.doi:10.3847/1538-4357/ac9d8d.hdl:10871/132423.
  13. ^abc Stelzer, B.; Burwitz, V. (May 2003). "Castor A and Castor B resolved in a simultaneous Chandra and XMM-Newton observation".Astronomy and Astrophysics.402(2): 719–728.arXiv:astro-ph/0302570.Bibcode:2003A&A...402..719S.doi:10.1051/0004-6361:20030286.S2CID15268418.
  14. ^ab Smith, M.A. (April 1974). "Metallicism in border regions of the Am domain. III. Analysis of the hot stars Alpha Geminorum A and B and Theta Leonis".Astrophysical Journal.189:101–111.Bibcode:1974ApJ...189..101S.doi:10.1086/152776.
  15. ^ab 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.S2CID18475298.
  16. ^abcdef Tokovinin, A.A. (1997)."MSC: A catalogue of physical multiple stars".Astronomy and Astrophysics Supplement Series.124(1): 75–84.Bibcode:1997A&AS..124...75T.doi:10.1051/aas:1997181.ISSN0365-0138.
  17. ^Hussain, G.A.J.; Brickhouse, N.S.; Dupree, A.K.; Reale, F.; Favata, F.; Jardine, M.M. (June 2012)."Chandra study of the eclipsing M dwarf binary, YY Gem".Monthly Notices of the Royal Astronomical Society.423(1): 493−504.Bibcode:2012MNRAS.423..493H.doi:10.1111/j.1365-2966.2012.20894.x.hdl:10447/73026.
  18. ^ Heintz, W.D. (1980). "Micrometer observations of double stars and new pairs – Part Ten".The Astrophysical Journal Supplement Series.44:111.Bibcode:1980ApJS...44..111H.doi:10.1086/190686.ISSN0067-0049.
  19. ^ Butler, C.J.; Erkan, N.; Budding, E.; Doyle, J.G.; Foing, B.; Bromage, G.E.; et al. (February 2015)."A multiwavelength study of the M dwarf binary YY Geminorum".Monthly Notices of the Royal Astronomical Society.446(4): 4205–4219.arXiv:1501.03930.Bibcode:2015MNRAS.446.4205B.doi:10.1093/mnras/stu2398.
  20. ^ Knobel, E.B. (June 1895)."Al Achsasi al Mouakket, on a catalogue of stars in theCalendariumof Mohammad al Achsasi al Mouakket ".Monthly Notices of the Royal Astronomical Society.55(8): 429.Bibcode:1895MNRAS..55..429K.doi:10.1093/mnras/55.8.429.
  21. ^(in Chinese)Trung Quốc chòm sao thần thoại,written by trần lâu kim. Published by Đài Loan thư phòng xuất bản công ty hữu hạn, 2005,ISBN978-986-7332-25-7.
  22. ^"Lượng tinh trung anh đối chiếu biểu"[Chinese-English Comparison Table of Bright Stars]. Nghiên cứu tài nguyên [Research Resources] (in Chinese). Hong Kong vũ trụ quán [Hong Kong Space Museum]. Archived fromthe originalon 29 September 2009.Retrieved23 November2010.
  23. ^ "IAU Working Group on Star Names (WGSN)".IAU Working Groups.International Astronomical Union.Retrieved22 May2016.
  24. ^ "Bulletin of the IAU Working Group on Star Names"(PDF).International Astronomical Union.Retrieved28 July2016.

External links[edit]

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