Omicron2 Canis Majoris (ο2 CMa, ο2 Canis Majoris) is astar in theconstellationCanis Major. Since 1943, thespectrum of this star has served as one of the stable anchor points by which other stars are classified.[3] It has anapparent visual magnitude of 3.043,[2] making it one of the brighter members of the constellation. Based upon adistance modulus of 10.2, it is about 3,600 light-years from Earth.[5]
This is a massivesupergiant star with astellar classification of B3 Ia,[3] indicating that, at the age of around 7 million years,[6] it has exhausted the supply of hydrogen at its core and is now undergoingnuclear fusion of helium to generate energy.[8] It has about 21[6] times the mass of the Sun and 65[5] times the Sun's radius. In all likelihood, it will end its life as aType II supernova.[8]
Omicron2 Canis Majoris is one of themost luminous stars known, as it radiates about 220,000[5] times as much luminosity as the Sun from itsouter envelope at a temperature of 15,500 K.[5] At this heat, the star is glowing with the blue-white hue of a B-type star.[9] This star is classified as anAlpha Cygni-typevariable 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 itsstellar wind at the rate of around2×10−9 times the mass of the Sun per year, or the equivalent of the Sun's mass every 500 million years.[10]
While this star lies in the field of view of theopen cluster namedCollinder 121, it is unlikely to be a member. In fact, its optical neighbor, the orange supergiantο1 Canis Majoris has a much higher likelihood of 23.1% based upon itsproper motion being a closer match to the motion of the cluster.[11] Although they are located near each other on thecelestial sphere, ο1 CMa and ο2 CMa are notgravitationally bound to each other as they appear to lie many light years apart.[12][8]
In the catalogue of stars in theCalendarium of Al Achsasi Al Mouakket, this star was designatedThanih al Adzari (ثاني ألعذاري -thaanii al-aðārii), which was translated intoLatin asSecunda Virginum, meaningthe second virgin.[13] This star, along withε CMa (Adhara),δ CMa (Wezen) andη CMa (Aludra), wereAl ʽAdhārā (ألعذاري), the Virgins.[14][15]
^Using Omicron2'sdistance modulus of 10.2, its distance from Earth can be calculated by the following equation: 10.2 = 5 • log(distance in parsecs)−5. GeoGebra can be used to calculate the distance value.
^abcdGutierrez-Moreno, Adelina; et al. (1966), "A System of photometric standards",Publications of the Department of Astronomy University of Chile,1, Publicaciones Universidad de Chile, Department de Astronomy:1–17,Bibcode:1966PDAUC...1....1G
^Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket",Monthly Notices of the Royal Astronomical Society,55:429–438,Bibcode:1895MNRAS..55..429K,doi:10.1093/mnras/55.8.429
^ε CMa asAoul al Adzari orPrima Virginum (the first virgin), ο2 CMa asThanih al Adzari orSecunda Virginum (the second virgin) andδ CMa asThalath al Adzari orTertia Virginum (the third virgin).η CMa should beRabah al Adzari orQuarta Virginum (the fourth virgin) consistently, but it was given by the nameAludra, meaningthe virgin (same meaning with Adhara (ε CMa) orAl ʽAdhārā)
