Xi Geminorum

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Xi Geminorum
Diagram showing star positions and boundaries of the Gemini constellation and its surroundings
Cercle rouge 100%.svg
Location of ξ Geminorum (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Gemini
Right ascension  06h 45m 17.36432s[1]
Declination +12° 53′ 44.1311″[1]
Apparent magnitude (V) 3.35[2]
Spectral type F5 IV-V[3]
U−B color index +0.06[4]
B−V color index +0.43[4]
Radial velocity (Rv)+25.6[2] km/s
Proper motion (μ) RA: –115.73[1] mas/yr
Dec.: –190.55[1] mas/yr
Parallax (π)55.56 ± 0.19[1] mas
Distance58.7 ± 0.2 ly
(18.00 ± 0.06 pc)
Absolute magnitude (MV)2.14[5]
Mass1.706 ± 0.012[6] M
Radius2.710 ± 0.021[6] R
Luminosity11.574 ± 0.238[6] L
Surface gravity (log g)3.81 ± 0.02[7] cgs
Temperature6,480 ± 39[6] K
Metallicity [Fe/H]0.00 ± 0.01[7] dex
Rotational velocity (v sin i)66.1 ± 3.3[8] km/s
Age1.5[9] Gyr
Other designations
31 Geminorum, HR 2484, HD 48737, BD+13°1396, FK5 256, HIP 32362, SAO 96074
Database references

Xi Geminorum (ξ Geminorum, abbreviated Xi Gem, ξ Gem), formally named Alzirr /ˈælzər/,[10] is a star in the zodiac constellation of Gemini. It forms one of the four feet of the outline demarcating the Gemini twins.[11] The star has an apparent visual magnitude of 3.35,[2] which is bright enough for it to be seen with the naked eye. From stellar parallax measurements, its distance from the Sun can be estimated as 58.7 light-years (18.0 parsecs).[1]


ξ Geminorum (Latinised to Xi Geminorum) is the star's Bayer designation.

It bore the traditional name of Al Zirr or Alzirr, from the Arabic الزِرّ al-zirr "the button".[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN approved the name Alzirr for this star on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.[10]

This star, along with Gamma Geminorum (Alhena), Mu Geminorum, Nu Geminorum and Eta Geminorum were al-hanʽah "the brand" (on the neck of the camel). They also were associated in al-nuḥātai, the dual form of al-nuḥāt, "the camel's hump".[12]

In Chinese, 井宿 (Jǐng Su), meaning Well (asterism), refers to an asterism consisting of Xi Geminorum, Mu Geminorum, Nu Geminorum, Gamma Geminorum, Epsilon Geminorum, 36 Geminorum, Zeta Geminorum and Lambda Geminorum.[14] Consequently, Xi Geminorum itself is known as 井宿四 (Jǐng Su sì, English: the Fourth Star of Well.)[15]


Although generally considered a single star, there is some evidence that Xi Geminorum may instead be a spectroscopic binary system consisting of two component stars of equal mass.[16]

Xi Geminorum has a stellar classification of F5 IV-V, which is subgiant star that is in the process of evolving away from the main sequence of stars like the Sun. It has about 162%[5] of the Sun's mass and is radiating more than 11 times the luminosity of the Sun.[7] This energy is being emitted from the outer envelope of the star at an effective temperature of 6,464 K.[7] This causes the star to take on the yellow-white hue common to F-type stars.[17]

X-ray emission has been detected from this star, which has an estimated X-ray luminosity of 1.06 × 1029 erg s−1.[5] It has the spectroscopic signature of a rapidly rotating star, with a projected rotational velocity of about 66 km s−1.[8]


  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:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. ^ a b c Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35), Bibcode:1999VeARI..35....1W
  3. ^ Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Robinson, P. E. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I". The Astronomical Journal. 126 (4): 2048. arXiv:astro-ph/0308182. Bibcode:2003AJ....126.2048G. doi:10.1086/378365.
  4. ^ a b Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  5. ^ a b c Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P
  6. ^ a b c d Boyajian, Tabetha S.; et al. (February 2012), "Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars", The Astrophysical Journal, 746 (1): 101, arXiv:1112.3316, Bibcode:2012ApJ...746..101B, doi:10.1088/0004-637X/746/1/101. See Table 10 & 12.
  7. ^ a b c d Pijpers, F. P. (March 2003), "Selection criteria for targets of asteroseismic campaigns", Astronomy and Astrophysics, 400: 241–248, arXiv:astro-ph/0303032, Bibcode:2003A&A...400..241P, doi:10.1051/0004-6361:20021839
  8. ^ a b Reiners, A. (January 2006), "Rotation- and temperature-dependence of stellar latitudinal differential rotation", Astronomy and Astrophysics, 446 (1): 267–277, arXiv:astro-ph/0509399, Bibcode:2006A&A...446..267R, doi:10.1051/0004-6361:20053911
  9. ^ Holmberg, J.; Nordstrom, B.; Andersen, J. (July 2009). "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics". Astronomy and Astrophysics. 501 (3): 941–947. arXiv:0811.3982. Bibcode:2009A&A...501..941H. doi:10.1051/0004-6361/200811191.
  10. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  11. ^ O'Meara, Stephen James (2002), The Caldwell objects, Deep-sky companions, Cambridge University Press, p. 185, ISBN 0-521-82796-5
  12. ^ a b Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 234. ISBN 0-486-21079-0. Retrieved 2010-12-12.
  13. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  14. ^ ‹See Tfd›(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.
  15. ^ ‹See Tfd›(in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived October 25, 2008, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  16. ^ Fuhrmann, K.; et al. (March 2011), "BESO échelle spectroscopy of solar-type stars at Cerro Armazones", Monthly Notices of the Royal Astronomical Society, 411 (4): 2311–2318, Bibcode:2011MNRAS.411.2311F, doi:10.1111/j.1365-2966.2010.17850.x
  17. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16

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