Castor (star)

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Template:Short description

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Castor
Template:Location mark
Location of Castor (circled)
Characteristics
A
Spectral type A1V + dM1e[1]
B−V Template:Engvar +0.03[2]
B
Spectral type Am + dM1e[1]
B−V Template:Engvar +0.04[2]
C
Spectral type dM1e + dM1e[1]
U−B Template:Engvar +1.04[3]
B−V Template:Engvar +1.49[3]
Variable type BY Dra[4]
Astrometry
AB
Radial velocity (Rv)5.40[5] km/s
Proper motion (μ) RA: −175.88 mas/yr[6]
Dec.: −99.28 mas/yr[6]
Parallax (π)66.356±0.041 mas[6]
DistanceTemplate:Val ly
(Template:Val pc)[6]
Absolute magnitude (MV)+0.986 / +1.886[2]
C
Radial velocity (Rv)+2.5[7] km/s
Proper motion (μ) RA: –201.406 mas/yr[8]
Dec.: –97.000 mas/yr[8]
Parallax (π)66.3110±0.0238 mas[8]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)+8.950[9]
Details
α Geminorum Aa
MassTemplate:Val[6] Template:Solar mass
RadiusTemplate:Val[6] Template:Solar radius
Surface gravity (log g)4.2[10] cgs
Temperature10,286[11] K
Rotational velocity (v sin i)18[12] km/s
Age290[6] Myr
α Geminorum Ab
MassTemplate:Val[6] Template:Solar mass
Metallicity [Fe/H] dex
α Geminorum Ba
MassTemplate:Val[6] Template:Solar mass
RadiusTemplate:Val[6] Template:Solar radius
Surface gravity (log g)4.0[10] cgs
Temperature8,842[11] K
Rotational velocity (v sin i)33[12] km/s
α Geminorum Bb
MassTemplate:Val[6] Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
α Geminorum Ca/Cb (components are identical)
Mass0.5992[9] Template:Solar mass
Radius0.6191[9] Template:Solar radius
Luminosity0.0733[9] Template:Solar luminosity
Surface gravity (log g)4.6317[9] cgs
Temperature3,820[9] K
Metallicity [Fe/H]~0.0[9] dex
Rotational velocity (v sin i)37[9] km/s
Age370[9] Myr
Metallicity [Fe/H]{{{metal_fe2}}} dex
Orbit[6]
Primaryα Geminorum A
Companionα Geminorum B
Period (P)Template:Val yr
Semi-major axis (a)Template:Val
(101 AU)Template:Efn
Eccentricity (e)Template:Val
Inclination (i)Template:Val°
Longitude of the node (Ω)41.3°
Periastron epoch (T)2,436,785
Argument of periastron (ω)
(secondary)		251.84°
Orbit[6]
Primaryα Geminorum Aa
Companionα Geminorum Ab
Period (P)Template:Val days
Semi-major axis (a)Template:Val
(Template:Solar radius calculator)Template:Efn
Eccentricity (e)Template:Val
Inclination (i)Template:Val°
Longitude of the node (Ω)Template:Val°
Periastron epoch (T)HJD−2,400,000 = 55,817.79
Argument of periastron (ω)
(primary)		Template:Val°
Semi-amplitude (K1)
(primary)		Template:Val km/s
Orbit[6]
Primaryα Geminorum Ba
Companionα Geminorum Bb
Period (P)Template:Val days
Semi-major axis (a)Template:Val
(Template:Solar radius calculator)Template:Efn
Inclination (i)Template:Val°
Longitude of the node (Ω)Template:Val°
Periastron epoch (T)HJD−2,400,000 = 56,705.49
Semi-amplitude (K1)
(primary)		Template:Val km/s
Orbit[13]
Primaryα Geminorum AB
Companionα Geminorum C
Period (P)14,000 yr
Orbit[9]
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
Template:Odlist
A: Template:Odlist
B: Template:Odlist
C: Template:Odlist
Database references
SIMBADdata
Castor A
Castor B
Castor C (YY Gem)

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Castor is the second-brightest object in the zodiac constellation of Gemini. It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem. With an apparent visual magnitude of 1.58, it is one of the brightest stars in the night sky. Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs. Although it is the 'α' (alpha) member of the constellation, it is half a magnitude fainter than 'β' (beta) Geminorum, Pollux.

Stellar system

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Castor is a multiple star system made up of six individual stars; there are three visual components, all of which are spectroscopic binaries. Appearing to the naked eye as a single star, Castor was first recorded as a double star in 1718 by James Pound, but it may have been resolved into at least two sources of light by Cassini as early as 1678. The separation between the binary systems Castor A and Castor B has increased from about 2″ (2 arcseconds of angular measurement) in 1970 to about 6″ in 2017.[15][13] These pairs have magnitudes of 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 an eclipsing binary with additional variations due to areas of different brightness on the surface of one or both stars, as well as irregular flares.[9] 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.[13]

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

Physical properties

Castor is 49 light-years away from Earth, determined from its large annual parallax.[6]

The two brightest stars are both A-type main-sequence stars, more massive and brighter than the Sun. The properties of their red dwarf companions are difficult to determine, but they are known to have masses 39% that of the Sun.[6]

File:YYGemLightCurve.png
A visual band light curve for YY Geminorum (Castor C), adapted from Butler et al. (2015)[16]

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

Castor C is a variable star, classified as a BY Draconis type. BY Draconis variables are cool dwarf stars which vary as they rotate due to starspots or other variations in their photospheres. The two red dwarfs of Castor C are almost identical, with masses around Template:Solar mass and luminosities less than 10% of the Sun.[9] Since 2018 it is suspected a brown dwarf with a mass at least Template:Val times the mass of Jupiter might be orbiting Castor C with a period of 50 years. If it is confirmed, Castor would turn out to be a seven-star system.[17]

All the red dwarfs in the Castor system have emissions lines in their spectra, and all are flare stars.[10]

Etymology and culture

α Geminorum (Latinised to Alpha Geminorum) is the star system's Bayer designation.

Castor and Pollux are the two "heavenly twin" stars that give the constellation Gemini (meaning twins in Latin) its name. The name Castor refers specifically to Castor, one of the twin sons of Zeus and Leda in Greek and Roman mythology.

The star was annotated by the Arabic description Al Ras al Taum al Muqadim, which translates as the head of the foremost twin. In the catalogue of stars in the Calendarium of al Achsasi al Mouakket, this star was designated Aoul al Dzira, which was translated into Latin as Prima Brachii, meaning the first in the paw.[18]

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning North River, refers to an asterism consisting of Castor, Rho Geminorum, and Pollux.[19] Consequently, Castor itself is known as Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx.)[20]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[21] 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 included Castor for the star α Geminorum Aa.[22]

Castor C also has the variable-star designation YY Geminorum.

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See also

Notes

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References

Template:Reflist

External links

Template:Stars of Gemini Template:Portal bar Template:Sky

  1. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named pourbaix2004
  2. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named barrado
  3. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named ducati
  4. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named gcvs
  5. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rv
  6. ↑ a b c d e f g h i j k l m n o Cite error: Invalid <ref> tag; no text was provided for refs named torres2022
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named gcsrv
  8. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named dr3c
  9. ↑ a b c d e f g h i j k l Cite error: Invalid <ref> tag; no text was provided for refs named torres2002
  10. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named aaa402_719
  11. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named apj189_101
  12. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named aaa463_2_671
  13. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named tokovinin1997
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Hussain2012
  15. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Heintz1980
  16. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Butler
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Wolf2018
  18. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named knobel1895
  19. ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
  20. ↑ Script error: No such module "citation/CS1".
  21. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named WGSN
  22. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named WGSN1
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