Beta Canis Majoris

Beta Canis Majoris

Location of Β CMa (upper right).
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Right ascension 06h 22m 41.98535s[1]
Declination -17° 57′ 21.3073″[1]
Apparent magnitude (V) 1.985[2]
Characteristics
Spectral type B1 II-III[3]
U−B color index -0.99[2]
B−V color index -0.235[2]
Variable type Beta Cephei
Astrometry
Radial velocity (Rv) +33.7[4] km/s
Proper motion (μ) RA: -3.23[1] mas/yr
Dec.: -0.78[1] mas/yr
Parallax (π) 6.53 ± 0.66[1] mas
Distance approx. 500 ly
(approx. 150 pc)
Details
Mass 13.5 ± 0.5[5] M☉
Radius 7.5 ± 2.7[6] R☉
Surface gravity (log g) 3.79 ± 0.20[6]
Luminosity 25,000[6] L☉
Temperature 23,690[7] K
Metallicity [Fe/H] 0.04 ± 0.10[5] dex
Rotational velocity (v sin i) 31 ± 5[5] km/s
Age (12.4 ± 0.7) × 106[5] years
Other designations
Murzim, Mirzam, Mirza,[8] 2 Canis Majoris, HR 2294, BD−17°1467, HD 44743, SAO 151428, FK5 243, HIP 30324, GC 8223, CCDM 06227-1757.[9]

Beta Canis Majoris (β CMa, β Canis Majoris) is a star in the southern constellation of Canis Major, the 'greater dog', and is located at a distance of about 500 light-years (150 parsecs) from the Earth.[1] In the modern constellation it lies at the position of the dog's head. It has the traditional name Murzim, Al-Murzim or Mirzam,[8] which is derived from the Arabic (مرزم) for 'The Herald', and probably refers to its position, heralding Sirius in the night sky (i.e., rising before it).

In Chinese, 軍市 (Jūn Shì), meaning Market for Soldiers, refers to an asterism consisting of β Canis Majoris, ν3 Canis Majoris, 15 Canis Majoris, π Canis Majoris, ο1 Canis Majoris and ξ1 Canis Majoris.[10] Consequently, β Canis Majoris itself is known as 軍市一 (Jūn Shì yī, English: the First Star of Market for Soldiers.)[11]. From this Chinese name, the name Kuen She arose.[8]

Properties

Pulsation Cycles[5]
Frequency
(day–1)		 Amplitude
(km s–1)
3.9793 2.7
3.9995 2.6
4.1832 0.7

Murzim is a Beta Cephei variable that varies in apparent magnitude between +1.95 and +2.00 over a six-hour period, a change in brightness that is too small to be discerned with the naked eye.[12] It exhibits this variation in luminosity because of periodic pulsations in its outer envelope, which follow a complex pattern with three different cycles; all about six hours in length. The two dominant pulsation frequencies have a combined beat period of roughly 50 days.[5]

This star has a mass of about 13–14 times the mass of the Sun[5] with 5–10 times the Sun's radius.[6] The effective temperature of the star's outer envelope is about 23,690 K, which is much higher than the Sun's at 5,778 K. The energy emitted at the high temperature of the former is what gives this star a blue-white hue characteristic of a B-type star.[7] The estimated age of Murzim is 12–13 million years, which is long enough for a star of this mass to have evolved into a giant star. The stellar classification of B1 II-III[3] indicates that the spectrum matches a star part way between a giant star and a bright giant.

Beta Canis Majoris is located near the far end of the Local Bubble, a cavity in the local interstellar medium through which the Sun is traveling.

In culture

Murzim appears on the flag of Brazil, symbolising the state of Amapá.[13]

USS Murzim (AK-95) was a United States Navy Crater class cargo ship named after the star.

References

  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, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c Cousins, A. W. J. (1972), "UBV Photometry of Some Very Bright Stars", Monthly Notes of the Astronomical Society, Southern Africa 31: 69, Bibcode 1972MNSSA..31...69C 
  3. ^ 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 
  4. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode 1953QB901.W495..... 
  5. ^ a b c d e f g Mazumdar, A. et al. (November 2006), "An asteroseismic study of the β Cephei star β Canis Majoris", Astronomy and Astrophysics 459 (2): 589–596, Bibcode 2006A&A...459..589M, doi:10.1051/0004-6361:20064980 
  6. ^ a b c d Hubrig, S. et al. (June 2006), "Discovery of magnetic fields in the βCephei star ξ1 CMa and in several slowly pulsating B stars*", Monthly Notices of the Royal Astronomical Society: Letters 369 (1): L61–L65, Bibcode 2006MNRAS.369L..61H, doi:10.1111/j.1745-3933.2006.00175.x 
  7. ^ a b Zorec, J. et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics 501 (1): 297–320, Bibcode 2009A&A...501..297Z, doi:10.1051/0004-6361/200811147 
  8. ^ a b c Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, pp. 129–130, http://books.google.com/books?id=5xQuAAAAIAAJ&pg=PA129 
  9. ^ "V* bet CMa -- Variable Star of beta Cep type", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Beta+Canis+Majoris, retrieved 2012-01-02 
  10. ^ (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.
  11. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  12. ^ Kaler, James B., "MIRZAM (Beta Canis Majoris)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/mirzam.html, retrieved 2012-01-02 
  13. ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. http://www.fotw.net/flags/br_astro.html. 
Stars of Canis Major
Bayer
Flamsteed
Nearby
Other