Sigma Canis Majoris

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σ Canis Majoris
Canis Major constellation map.svg
Red circle.svg
Location of σ Canis Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Right ascension  07h 01m 43.14779s[1]
Declination –27° 56′ 05.3898″[1]
Apparent magnitude (V) 3.43 - 3.51[2]
Spectral type K4 III[3]
U−B color index +1.88[4]
B−V color index +1.73[4]
Variable type LC[2]
Radial velocity (Rv)+22.11[5] km/s
Proper motion (μ) RA: –5.98[1] mas/yr
Dec.: +4.59[1] mas/yr
Parallax (π)2.91 ± 0.19[1] mas
Distance1,120 ± 70 ly
(340 ± 20 pc)
Absolute magnitude (MV)–5.14[6]
Mass12.3 ± 0.1[7] M
Radius420[6] R
Luminosity31,000[6] L
Surface gravity (log g)1.00[8] cgs
Temperature3,750[6] K
Metallicity [Fe/H]+0.16[8] dex
Age16.4 ± 0.5[7] Myr
Other designations
Unurgunite, 22 Canis Majoris, ADS 5719, CD −27°3544, FK5 1183, HD 52877, HIP 33856, HR 2646, SAO 172797.[9]
Database references

Sigma Canis Majoris (σ Canis Majoris, abbreviated Sigma CMa, σ CMa), also named Unurgunite /ˌʌnərˈɡʌnt/,[10] is a variable star in the southern constellation of Canis Major. It is approximately 1,120 light-years (340 parsecs) from the Sun and has an average apparent visual magnitude of +3.41.


σ Canis Majoris (Latinised to Sigma Canis Majoris) is the system's Bayer designation. The star is identified with the nganurganity [ˈŋanuɾˌɡ̊aniɟ̊] "Jacky lizard"[11] in the culture of the Boorong, a clan of the indigenous Maligundidj people of northwestern Victoria in Australia, who saw it as an ancestral figure who fights the moon, flanked by his wives (the stars Delta and Epsilon Canis Majoris).[9][12] The name was transcribed by settler William Stanbridge as "Unurgunite" in the 1850’s. (Initial ng-, which does not occur in English, was typically ignored in transcription of that era.) In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN approved the name Unurgunite for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[10]


Sigma Canis Majoris is a supergiant star with a stellar classification of K4 III. This is a type of star that is in the late stages of its evolution, having consumed the hydrogen at its core and ballooned out to 420 times the Sun's radius.[6] At 1.95 Astronomical units,[14] this radius is nearly double the average distance of the Earth from the Sun. It is currently radiating about 32,000[15] times the luminosity of the Sun from its outer envelope at an effective temperature of around 3,877 K.[8] This gives it the cool orange-red hue of an M-type star.[16]


Sigma Canis Majoris was noted as a likely variable star in a list of bright southern stars studied at the Cape Observatory.[17] The variability was confirmed in 1963,[18] and it was formally catalogued as a variable star.[19]

It is classified as an irregular variable star and its brightness varies from magnitude +3.43 to +3.51. The magnetic field of this star has a strength below 1 G.[20] It is suspected of being a member of the Collinder 121 stellar association of co-moving stars,[6] but this is disputed.[21]


Sigma Canis Majoris is listed as a possible type II supernova. Instruments are capable of measuring the pre-supernova neutrino flux which would act as an alert that the supernova explosion was starting.[22]


  1. ^ a b c d e van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752v1, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 Note: see VizieR catalogue I/311.
  2. ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.
  3. ^ Abt, Helmut A (2008). "Visual Multiples. IX. MK Spectral Types". The Astrophysical Journal Supplement Series. 176: 216–217. Bibcode:2008ApJS..176..216A. doi:10.1086/525529.
  4. ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  5. ^ Mermilliod, J. C.; Mayor, M.; Udry, S. (July 2008), "Red giants in open clusters. XIV. Mean radial velocities for 1309 stars and 166 open clusters", Astronomy and Astrophysics, 485 (1): 303–314, Bibcode:2008A&A...485..303M, CiteSeerX, doi:10.1051/0004-6361:200809664
  6. ^ a b c d e f Levesque, Emily M.; et al. (August 2005), "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought", The Astrophysical Journal, 628 (2): 973–985, arXiv:astro-ph/0504337, Bibcode:2005ApJ...628..973L, doi:10.1086/430901
  7. ^ a b Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x
  8. ^ a b c Mallik, Sushma V. (October 1998), "Chromospheric activity in cool stars and the lithium abundance", Astronomy and Astrophysics, 338: 623–636, Bibcode:1998A&A...338..623M
  9. ^ a b Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae" (PDF). Journal of Astronomical History & Heritage. 13 (3): 220–34. arXiv:1010.4610. Bibcode:2010JAHH...13..220H.
  10. ^ a b "Naming Stars". Retrieved 16 December 2017.
  11. ^ Literally "waddy-tailed goanna", from nganurr 'black goanna' + gani 'waddy' + genitive suffix -ity/-itj.
  12. ^ "IAU Approves 86 New Star Names From Around the World" (Press release). 11 December 2017.
  13. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  14. ^ 1 solar radius = 0.0046491 Astronomical Units, so 420 × 0.00465 = 1.95.
  15. ^ Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics, 352: 495–507, Bibcode:1999A&A...352..495M
  16. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
  17. ^ Cousins, A. W. J. (1951). "Bright variable stars in southern hemisphere (first list)". The Observatory. 71: 199. Bibcode:1951Obs....71..199C.
  18. ^ Cousins, A. W. J. (1963). "Red Variable Stars of Small Range Amongst the Bright Stars". Monthly Notes of the Astron. Soc. Southern Africa. 22: 133. Bibcode:1963MNSSA..22..133C.
  19. ^ Kukarkin, B. V.; Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (1973). "59th Name-List of Variable Stars". Information Bulletin on Variable Stars. 834: 1. Bibcode:1973IBVS..834....1K.
  20. ^ Grunhut, J. H.; et al. (November 2010), "Systematic detection of magnetic fields in massive, late-type supergiants", Monthly Notices of the Royal Astronomical Society, 408 (4): 2290–2297, arXiv:1006.5891, Bibcode:2010MNRAS.408.2290G, doi:10.1111/j.1365-2966.2010.17275.x
  21. ^ de Zeeuw, P. T.; et al. (January 1999), "A HIPPARCOS Census of the Nearby OB Associations", The Astronomical Journal, 117 (1): 354–399, arXiv:astro-ph/9809227, Bibcode:1999AJ....117..354D, doi:10.1086/300682
  22. ^ Asakura, K.; Gando, A.; Gando, Y.; Hachiya, T.; Hayashida, S.; Ikeda, H.; Inoue, K.; Ishidoshiro, K.; Ishikawa, T.; Ishio, S.; Koga, M.; Matsuda, S.; Mitsui, T.; Motoki, D.; Nakamura, K.; Obara, S.; Oura, T.; Shimizu, I.; Shirahata, Y.; Shirai, J.; Suzuki, A.; Tachibana, H.; Tamae, K.; Ueshima, K.; Watanabe, H.; Xu, B. D.; Kozlov, A.; Takemoto, Y.; Yoshida, S.; et al. (2016). "KamLAND Sensitivity to Neutrinos from Pre-supernova Stars". The Astrophysical Journal. 818: 91. arXiv:1506.01175. Bibcode:2016ApJ...818...91A. doi:10.3847/0004-637X/818/1/91.