OMI-2 CMA (Omicron-2 Canis Majoris). Down below brilliant Sirius in Canis Major (as viewed from the northern hemisphere, up above it as seen from the southern) lies a notable triangle of bright stars made of Adhara (Epsilon Canis Majoris), Wezen (Delta), and Aludra (Eta). The old Arabs referred to the trio as "the Virgins," and included among them a lesser-known star between Wezen and Sirius with no proper name, and which Bayer chose to call "Omicron-2." Its Greek letter mate, to which the star is not gravitationally attached, Omicron-1, lies two degrees to the west. Though at mid-third magnitude (3.02) visually fainter than the Dog's more famed stars, Omi-2 still fits right in as quite the magnificent star. It is a glorious blue class B (B3) supergiant 2500 light years away that lights its surroundings with the radiance of 110,000 Suns, after correction for a small bit of dimming by interstellar dust and a rather large amount of ultraviolet radiation from its 14,700 Kelvin surface. As a supergiant, it is in the process of evolving, the luminosity and temperature telling of a 20 solar mass star. Some eight million years old, Omi-2 ceased core hydrogen fusion only about 15,000 years ago, and has already begun to fuse the resulting core helium into carbon and oxygen. The star's only fate seems to be to explode as a supernova. Omi-2's relation with the orange class K supergiant Omi-1 has long been argued. Though not in any way a double star, they seem to be part of an extended loose association of O and B stars (that also includes Wezen) sometimes called "Collinder 121" after the real cluster that seems to surround Omi-2 (but that actually lies far in the background). Omi-1, 2000 light years away, is a bit closer, but the errors on the measurements are great enough that they could still be at the same distance. At best, they at least 70 light years apart, at worst a couple hundred. Yet they were probably born more or less at the same time from the same complex of interstellar matter, and are now slowly moving apart. Thanks to Jeff Bryan, who suggested this star.
Written by Jim Kaler. Return to STARS.