Sigma Canis Majoris

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Sigma Canis Majoris
Diagram showing star positions and boundaries of the Canis Major constellation and its surroundings
Cercle rouge 100%.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) +3.41[2]
Spectral type M1.5 Iab[3]
U−B color index +1.75[2]
B−V color index +1.69[2]
Radial velocity (Rv) +22.11[4] 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
Distance 1,120 ± 70 ly
(340 ± 20 pc)
Absolute magnitude (MV) –5.14[5]
Mass 12.3 ± 0.1[6] M
Radius 420[5] R
Luminosity 32,000[7] L
Surface gravity (log g) 1.00[8] cgs
Temperature 3,877[8] K
Metallicity [Fe/H] +0.16[8] dex
Age 16.4 ± 0.5[6] Myr
Other designations
22 Canis Majoris, ADS 5719, CD −27° 3544, FK5 1183, HD 52877, HIP 33856, HR 2646, SAO 172797,[9] Unurgunite.[10]

Sigma Canis Majoris (σ CMa, σ Canis Majoris) is a star in the southern constellation of Canis Major. It is approximately 1,120 light-years (340 parsecs) from Earth[1] and has an average apparent visual magnitude of +3.41.[2]

σ CMa is a supergiant star with a stellar classification of M1.5 Iab.[3] 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.[5] At 1.95 Astronomical Units,[11] this is radius nearly double the average distance of the Earth from the Sun. It is currently radiating about 32,000[7] 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.[12]

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.[3] It is suspected of being a member of the Collider 121 stellar association of co-moving stars,[5] but this is disputed.[13]

Culture signification[edit]

The indigenous Boorong people of northwestern Victoria saw it as Unurgunite, flanked by his wives (Epsilon and Delta Canis Majoris).[10]


  1. ^ a b c d e f 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 c d Fernie, J. D. (May 1983), "New UBVRI photometry for 900 supergiants", Astrophysical Journal Supplement Series 52: 7–22, Bibcode:1983ApJS...52....7F, doi:10.1086/190856 
  3. ^ a b c 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 
  4. ^ 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, doi:10.1051/0004-6361:200809664 
  5. ^ a b c d 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 
  6. ^ 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 
  7. ^ a b Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics 352: 495–507, Bibcode:1999A&A...352..495M 
  8. ^ a b c d 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. ^ "sig CMa -- Pulsating variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg) 
  10. ^ 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. 
  11. ^ 1 solar radius = 0.0046491 Astronomical Units, so 420 × 0.00465 = 1.95.
  12. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  13. ^ 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