WEZEN (Delta Canis Majoris). Shining at third rank in Canis Major, the Greater Dog, at bright second magnitude (1.84), Wezen is not far behind the Dog's Adhara. It nevertheless received Bayer's Delta designation, Gamma going to much fainter Muliphein, which lies just up and to the left of Sirius. Part of the small asterism that the Arabs knew as "the Virgins" (which incorporates the triangle below Sirius, and includes Adhara), the name literally means, from Arabic, "weight," as in heavy. Wezen was, however, part of a pair of names originally applied to a pair of stars, "Wezen" and "Hadari," whose identities are not really known. Wezen was later assigned to our Delta, to which it certainly did not originally belong, whereas Hadari (as Hadar) is now given to Beta Centauri (to which it may have belonged). Whatever the origin, Delta is Wezen now. The name surfaces for Beta Columbae, and also, in a very strange form, for Muliphein (Gamma). Oddly, "weight" is a wonderful name for this magnificent star, as it is indeed "weighty," as in massive; it is certainly one of the more massive that grace the naked-eye nightly sky. Wezen is also one of the most distant and luminous. Ranking thirteenth in the second magnitude camp even though 1800 light years away, it shines with a fierce luminosity 50,000 times that of the Sun. Wezen is also of a rare evolutionary breed, a full-blown yellow supergiant of class F with a temperature of 6200 Kelvin, not much more than our Sun. From luminosity and temperature, we derive a supergiant radius 195 times that of the Sun, which makes the star almost as big as the Earth's orbit. As far away as it is, Wezen is so big that we can still discern it as a disk, from which a very consistent radius of 205 times solar is found. From its measured rotation speed of 28 kilometers per second, the star may take up to a year just to turn once. Calculations of the stellar aging process clearly show that Wezen weighs in at about 17 solar masses. It is only about 10 million years old, yet has still ceased hydrogen fusion in its core (the Sun's hydrogen fusion lasts 10 billion years!). The core is now contracting and heating, and will fire up helium fusion in less than 100,000 years, when the outer part of the star has become a red supergiant something like Antares. Internal nuclear fusion, the steady evolution, and the stirring of internal gases have altered the chemical composition of Wezen's surface, the nitrogen abundance twice normal, sodium up by a factor of 6. Wezen has only one known end: it will fuse its core into iron, which then will collapse to create a brilliant explosion, a supernova; the core will most likely become a neutron star about the size of a small town, while the outer portions of the star will be shattered and sent back to interstellar space full of chemically enriched gases that include a huge quantity of freshly made iron.
Written by Jim Kaler. Return to STARS.