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.