Mu Geminorum

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μ Geminorum
Gemini constellation map.svg
Red circle.svg
Location of μ Geminorum (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Gemini
Right ascension 06h 22m 57.62686s[1]
Declination +22° 30′ 48.8979″[1]
Apparent magnitude (V) 2.857[2]
Spectral type M3 III[3]
B−V color index +1.643[2]
Variable type LB[4]
Radial velocity (Rv) +54.38 ± 0.24[5] km/s
Proper motion (μ) RA: +56.39[1] mas/yr
Dec.: –110.03[1] mas/yr
Parallax (π) 14.08 ± 0.71[1] mas
Distance 230 ± 10 ly
(71 ± 4 pc)
Absolute magnitude (MV) −1.42[6]
Mass 2.1[7] M
Luminosity 2,799[8] L
Surface gravity (log g) 1.50[8] cgs
Temperature 3,773[8] K
Rotational velocity (v sin i) 8.4[9] km/s
Other designations
Tejat, mu Geminorum, 13 Geminorum, ADS 4990A, BD+22°1304, CCDM J06230+2230A, FK5 241, HD 44478, HIP 30343, HR 2286, SAO 78297.[10]
Database references

Mu Geminorum (μ Geminorum, abbreviated Mu Gem, μ Gem) is a double star[11] in the northern constellation of Gemini.

The system consists of a bright single star (designated Mu Geminorum A, also named Tejat[12]) and a dimmer companion (Mu Geminorum BC), itself a binary pair.[11]


μ Geminorum (Latinised to Mu Geminorum) is the system's Bayer designation. The designations of the two constituents as Mu Geminorum A and BC derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[13]

The system bore the traditional name of Tejat or Tejat Posterior which means 'back foot', because it is the foot of Castor, one of the Gemini twins. The name Tejat Posterior was formerly applied to an asterism consisting of this star, along with Gamma Geminorum (Alhena), Nu Geminorum, Eta Geminorum (Propus), and Xi Geminorum (Alzirr).[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Tejat for the primary component on February 1, 2017 and it is now so included in the List of IAU-approved Star Names.[12]

The names Calx (Latin, meaning 'heel'), Pish Pai (from the Persian پیش‌پای ('pīshpāy', meaning 'foreleg'), and Nuhatai (from Arabic 'Al Nuḥātai', the dual form of 'Al Nuḥāt', 'a Camel's Hump') have also been applied to Mu Geminorum.[15]

In Chinese, 井宿 (Jǐng Su), meaning Well (asterism), refers to an asterism consisting of Mu Geminorum, Gamma Geminorum, Nu Geminorum, Xi Geminorum, Epsilon Geminorum, 36 Geminorum, Zeta Geminorum and Lambda Geminorum.[16] Consequently, Mu Geminorum itself is known as 井宿一 (Jǐng Su yī, English: the First Star of Well.)[17]


μ Gem is the star on the left, surrounded by the S249 nebula. The bright star on the right, near the IC 443 supernova remnant, is η Gem.

Mu Geminorum has an average apparent visual magnitude of 2.9,[2] which makes it the fourth-brightest member of Gemini. Because the star lies near the ecliptic it is subject to occultations by the Moon,[18] from parallax measurements made during the Hipparcos mission, the distance to this star is roughly 230 light-years (71 parsecs).[1] Its visual magnitude is diminished by 0.07 as a result of extinction from intervening gas and dust.[5]

This system is a slow irregular variable of type LB, its brightness varies between magnitude +2.75 and +3.02 over a 72-day period, along with a 2,000-day period of long term variation. It is a red giant at a stellar classification of M3 III,[3] with a surface temperature of 3,773 K,[8] meaning it is brighter, yet cooler, than the Sun.[4][11] The star is currently on the asymptotic giant branch and is generating energy through the nuclear fusion of hydrogen and helium along concentric shells surrounding an inert core of carbon and oxygen.[19]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c Gutierrez-Moreno, Adelina; et al. (1966), A System of photometric standards, 1, Publicaciones Universidad de Chile, Department de Astronomy, pp. 1–17, Bibcode:1966PDAUC...1....1G. 
  3. ^ a b Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics, 11: 29, Bibcode:1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333. 
  4. ^ a b mu Gem[permanent dead link], entry in the Combined General Catalog of Variable Stars (GCVS4.2)[permanent dead link], N. N. Samus, O. V. Durlevich, et al., database identifier II/250 at the Centre de Données astronomiques de Strasbourg.
  5. ^ a b Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430 (1): 165–186, arXiv:astro-ph/0409579Freely accessible, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272. 
  6. ^ Schiavon, Ricardo P. (July 2007), "Population Synthesis in the Blue. IV. Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations", The Astrophysical Journal Supplement Series, 171 (1): 146–205, arXiv:astro-ph/0611464Freely accessible, Bibcode:2007ApJS..171..146S, doi:10.1086/511753. 
  7. ^ Tsuji, Takashi (May 2007), "Isotopic abundances of Carbon and Oxygen in Oxygen-rich giant stars", in Kupka, F.; Roxburgh, I.; Chan, K., Convection in Astrophysics, Proceedings of IAU Symposium #239 held 21-25 August, 2006 in Prague, Czech Republic, pp. 307–310, arXiv:astro-ph/0610180Freely accessible, Bibcode:2007IAUS..239..307T, doi:10.1017/S1743921307000622. 
  8. ^ a b c d Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics, 352: 495–507, Bibcode:1999A&A...352..495M. 
  9. ^ Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209. 
  10. ^ "mu. Gem". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 12, 2007. 
  11. ^ a b c d "Tejat". Jim Kaler's STARS. Retrieved 2017-03-31. 
  12. ^ a b "Naming Stars". Retrieved 16 December 2017. 
  13. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707Freely accessible [astro-ph.SR]. 
  14. ^ "International Astronomical Union | IAU". Retrieved 2017-04-01. 
  15. ^ Allen, Richard Hinckley (1899), Star-names and Their Meanings, G. E. Stechert, p. 236 
  16. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  17. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-08-19 at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
  18. ^ White, Nathaniel M.; Feierman, Barry H. (September 1987), "A Catalog of Stellar Angular Diameters Measured by Lunar Occultation", Astronomical Journal, 94: 751, Bibcode:1987AJ.....94..751W, doi:10.1086/114513. 
  19. ^ Lebzelter, T.; Hron, J. (January 2008), "BRITE stars on the AGB", Communications in Asteroseismology, 152: 178–181, Bibcode:2008CoAst.152..178L, doi:10.1553/cia152s178. 

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