Beta Canis Minoris

Beta Canis Minoris (β Canis Minoris, abbreviated Beta CMi, β CMi), also named Gomeisa /ɡɒˈmzə/,[12][13] is a star in the constellation of Canis Minor. In the night sky it is notable for its proximity to the prominent star Procyon.

Beta Canis Minoris
Position Beta Cmi.png
Position of Beta Canis Minoris.
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Minor
Right ascension 07h 27m 09.04174s[1]
Declination +08° 17′ 21.5368″[1]
Apparent magnitude (V) 2.84 - 2.92[2]
Spectral type B8 Ve[3]
U−B color index –0.28[4]
B−V color index –0.09[4]
Variable type γ Cas[2] + SPBe[3]
Radial velocity (Rv)+22[5] km/s
Proper motion (μ) RA: -59.375 ± 1.708[6] mas/yr
Dec.: -35.010 ± 1.368[6] mas/yr
Parallax (π)20.3535 ± 1.2220[6] mas
Distance160 ± 10 ly
(49 ± 3 pc)
Absolute magnitude (MV)−0.59[7]
Mass3.5[3] M
Radius3.5[8] R
Luminosity195[3] L
Surface gravity (log g)3.51[8] cgs
Temperature11,772[8] K
Rotational velocity (v sin i)210[9] km/s
[10] Myr
Other designations
Gomeisa, Algomeyla, Gomelza, 3 Canis Minoris, BD+08°1774, FK5 285, HD 58715, HIP 36188, HR 2845, IRAS 07244+0823, SAO 115456.[11]
Database references


β Canis Minoris (Latinised to Beta Canis Minoris) is the star's Bayer designation.

The traditional name Gomeisa comes from the Arabic al-ghumaisa' ("the bleary-eyed (woman)"),[14] short for مرزم الغميصاء mirzam al-ghumaisa' ("girdle of the bleary-eyed one"). In Arabic, the short form would be identical with the name of Procyon. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[16] included a table of the first two batches of names approved by the WGSN; which included Gomeisa for this star.

In Chinese, 南河 (Nán Hé), meaning South River, refers to an asterism consisting of β Canis Minoris, Procyon and Epsilon Canis Minoris.[17] Consequently, β Canis Minoris itself is known as 南河二 (Nán Hé èr, English: the Second Star of South River.)[18]


From parallax measurements, the distance to this star is about 160 ± 10 light-years (49.1 ± 3.1 parsecs). It has an apparent visual magnitude of 2.89,[4] making it easily visible to the naked eye. Beta Canis Minoris has about 3.5 times the Sun's mass and is rotating rapidly with a projected rotational velocity of 210 km s−1,[9] which gives a lower bound on the azimuthal rotational velocity along the star's equator. The actual rotation rate may be about once per day.[14]

The stellar classification of this star is B8 Ve.[3] A luminosity class V star belongs on the main sequence, which means it is generating energy through the thermonuclear fusion of hydrogen at its core. The star is radiating this energy from its outer envelope at an effective temperature of 12,050 K,[3] giving it a blue-white hue typical of B-type stars.[19] An 'e' classification indicates that the spectrum contains emission lines, which means this is a Be star that is surrounded by a thin, circumstellar disk made of gaseous material ejected from the star. This hot, gaseous disk is about three times the radius of the star.[3]


β Canis Minoris has long been suspected of variability,[20] and in 1977 it was classified as a γ Cassiopeiae variable in the General Catalogue of Variable Stars. A number of studies have found no variation at all.[21] While it shows little variation in brightness, it does display changes in the hydrogen emission coming from the gaseous disk but even those are less pronounced than in many other Be stars.[22]

Examination with the Canadian MOST space telescope reveals changes in the brightness of β Canis Minoris at the milli-magnitude level. This variation has a cyclic pattern formed from multiple overlapping frequencies, with the dominant frequencies being 3.257 and 3.282 cycles per day. As such, it belongs to a class called slowly pulsating B-type (SPB) stars. Be stars that show these types of pulsation have been dubbed SPBe stars.[3]

Possible companionEdit

It is likely that Beta Canis Minoris is a close binary with a 170-day, eccentric orbit. The companion would have about 42% of the Sun's mass. The nature of the companion is unknown, but it is speculated that it could be a subdwarf O star remaining after binary interactions that spun up the Be primary. If confirmed, this would make it a member of the very rare Phi Persei Be+sdO type systems.[22]


  1. ^ a b 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. S2CID 18759600.
  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. Bibcode:2009yCat....102025S.
  3. ^ a b c d e f g h Saio, H.; et al. (January 2007), "MOST Detects g-Modes in the Late-Type Be Star β Canis Minoris (B8 Ve)", The Astrophysical Journal, 654 (1): 544–550, arXiv:astro-ph/0609460, Bibcode:2007ApJ...654..544S, doi:10.1086/509315, S2CID 118836002
  4. ^ a b c 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. ^ Wilson, Ralph Elmer (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
  6. ^ a b c Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  7. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  8. ^ a b c Meilland, A.; Stee, Ph.; Chesneau, O.; Jones, C. (October 2009), "VLTI/MIDI observations of 7 classical Be stars", Astronomy and Astrophysics, 505 (2): 687–693, arXiv:0908.1239, Bibcode:2009A&A...505..687M, doi:10.1051/0004-6361/200911960, S2CID 12694072
  9. ^ a b Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590
  10. ^ Janson, Markus; et al. (August 2011), "High-contrast Imaging Search for Planets and Brown Dwarfs around the Most Massive Stars in the Solar Neighborhood", The Astrophysical Journal, 736 (2): 89, arXiv:1105.2577, Bibcode:2011ApJ...736...89J, doi:10.1088/0004-637X/736/2/89, S2CID 119217803
  11. ^ "bet CMi -- Be Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-09 CS1 maint: discouraged parameter (link)
  12. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  13. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. CS1 maint: discouraged parameter (link)
  14. ^ a b Kaler, James B., "GOMEISA (Beta Canis Minoris)", Stars, University of Illinois, retrieved 2012-01-09 CS1 maint: discouraged parameter (link)
  15. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. CS1 maint: discouraged parameter (link)
  16. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. CS1 maint: discouraged parameter (link)
  17. ^ (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.
  18. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2011-01-30 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  19. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16 CS1 maint: discouraged parameter (link)
  20. ^ Smart, W. M. (1936). "On a Suspected Variation in the Light of β Canis Minoris". Monthly Notices of the Royal Astronomical Society. 96 (3): 258–262. Bibcode:1936MNRAS..96..258S. doi:10.1093/mnras/96.3.258.
  21. ^ Bozic, H.; Muminovic, M.; Pavlovski, K.; Stupar, M.; Harmanec, P.; Horn, J.; Koubsky, P. (1982). "No Rapid Variability Observed for the Be Stars HD 58050 and β CMi". Information Bulletin on Variable Stars. 2123: 1. Bibcode:1982IBVS.2123....1B.
  22. ^ a b Dulaney, Nicholas A.; Richardson, Noel D.; Gerhartz, Cody J.; Bjorkman, J. E.; Bjorkman, K. S.; Carciofi, Alex C.; Klement, Robert; Wang, Luqian; Morrison, Nancy D.; Bratcher, Allison D.; Greco, Jennifer J.; Hardegree-Ullman, Kevin K.; Lembryk, Ludwik; Oswald, Wayne L.; Trucks, Jesica L. (2017). "A Spectroscopic Orbit for the Late-type Be Star β CMi". The Astrophysical Journal. 836 (1): 112. arXiv:1701.05201. Bibcode:2017ApJ...836..112D. doi:10.3847/1538-4357/836/1/112. S2CID 119370197.