Beta Canis Majoris
Epoch J2000 Equinox J2000
|Right ascension||06h 22m 41.98535s|
|Declination||−17° 57′ 21.3073″|
|Apparent magnitude (V)||1.985|
|Spectral type||B1 II-III|
|U−B color index||−0.99|
|B−V color index||−0.235|
|Variable type||Beta Cephei|
|Radial velocity (Rv)||+33.7 km/s|
|Proper motion (μ)||RA: −3.23 mas/yr
Dec.: −0.78 mas/yr
|Parallax (π)||6.53 ± 0.66 mas|
|Distance||approx. 500 ly
(approx. 150 pc)
|Mass||13.5 ± 0.5 M☉|
|Radius||9.7 ± 1.3 R☉|
|Surface gravity (log g)||3.79 ± 0.20 cgs|
|Metallicity [Fe/H]||0.04 ± 0.10 dex|
|Rotational velocity (v sin i)||31 ± 5 km/s|
|Age||12.4 ± 0.7 Myr|
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. In the modern constellation it lies at the position of the dog's head. It has the traditional name Murzim, Al-Murzim or Mirzam, 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. Consequently, β Canis Majoris itself is known as 軍市一 (Jūn Shì yī, English: the First Star of Market for Soldiers). From this Chinese name arose the name Kuen She.
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. 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.
This star has a mass of about 13–14 times the mass of the Sun with 8–11times the Sun's radius. The effective temperature of the star's outer envelope is about 23,150 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. 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 indicates that the spectrum matches a star part way between a giant star and a bright giant.
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