Omicron² Canis Majoris (ο² CMa, ο² Canis Majoris) is a star in the constellation Canis Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[3] It has an apparent visual magnitude of 3.043,[2] making it one of the brighter members of the constellation. The distance to this star is roughly 2,800 light years (800 parsecs), with a 34% margin of error.[1]

ο² Canis Majoris

Location of ο2 CMa (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Canis Major
Right ascension	07h 03m 01.47211s[1]
Declination	−23° 49′ 59.8523″[1]
Apparent magnitude (V)	3.043[2]
Characteristics
Spectral type	B3 Ia[3]
U−B color index	−0.778[2]
B−V color index	−0.107[2]
Variable type	α Cyg[4]
Astrometry
Radial velocity (Rv)	48.4[5] km/s
Proper motion (μ)	RA: −2.21[1] mas/yr Dec.: +3.61[1] mas/yr
Parallax (π)	1.18 ± 0.40 mas[1]
Distance	approx. 2,800 ly (approx. 800 pc)
Absolute magnitude (MV)	−7.3[6]
Details
Mass	21.4±2.2[7] M☉
Radius	65[6] R☉
Luminosity	220,000[6] L☉
Surface gravity (log g)	2.05[6] cgs
Temperature	15,500[6] K
Rotational velocity (v sin i)	58[6] km/s
Age	7.4±1.0[7] Myr
Other designations
24 Canis Majoris, CD−23°4797, FK5 270, HD 53138, HIP 33977, HR 2653, SAO 172839
Database references
SIMBAD	data

Properties

This is a massive supergiant star with a stellar classification of B3 Ia,[3] indicating that, at the age of around 7 million years,[7] it has exhausted the supply of hydrogen at its core and is now undergoing nuclear fusion of helium to generate energy.[9] It has about 21[7] times the mass of the Sun and 65[6] times the Sun's radius. In all likelihood, it will end its life as a Type II supernova.[9]

Omicron² Canis Majoris is one of the most luminous stars known, as it radiates about 220,000[6] times as much luminosity as the Sun from its outer envelope at a temperature of 15,500 K.[6] At this heat, the star is glowing with the blue-white hue of a B-type star.[10] This star is classified as an Alpha Cygni-type variable star that undergoes periodic non-radial pulsations, which cause its brightness to cycle from magnitude +2.93 to +3.08 over a 24.44 day interval.[4] It is losing mass from its stellar wind at the rate of around 2×10⁻⁹ times the mass of the Sun per year, or the equivalent of the Sun's mass every 500 million years.[11]

Collinder 121

While this star lies in the field of view of the open cluster named Collinder 121, it is unlikely to be a member. In fact, its optical neighbor, the orange supergiant ο¹ Canis Majoris has a much higher likelihood of 23.1% based upon its proper motion being a closer match to the motion of the cluster.[12] Although they are located near each other on the celestial sphere, ο¹ CMa and ο² CMa are most likely not gravitationally bound to each other as they appear to lie many light years apart.[1][9]

Name

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Thanih al Adzari (ثاني ألعذاري - thaanii al-aðārii), which was translated into Latin as Secunda Virginum, meaning the second virgin.[13] This star, along with ε CMa (Adhara), δ CMa (Wezen) and η CMa (Aludra), were Al ʽAdhārā (ألعذاري), the Virgins.[14][15]

References

На других языках

[es] Ómicron2 Canis Majoris

[ru] Омикрон² Большого Пса