GIENAH CORVI (Gamma Corvi). Gienah (je-nuh), an important star in
a prominent but small constellation, Corvus, the Crow or Raven, a very noticeable skewed box
that crosses the sky just to the west of first magnitude Spica in Virgo.
The name, from an Arabic phrase that means "the Raven's Wing," is
shared with Gienah in Cygnus (Epsilon Cygni), so to avoid confusion Corvus's
Gienah becomes Gienah Corvi (the Latin ending implying possession).
Gienah Corvi is the right-hand star at the top of the box and one
of the "pointers" to Spica (the other Algorab), as if Spica really needs such.
Though the brightest star in the constellation, just over the
second magnitude line to third (2.59), Bayer oddly gave it the Gamma
designation, Alpha (Alchiba)
a fourth magnitude star beneath the right-hand
side of the prominent box. Gienah is a class B (B8) blue-white
giant with a
temperature of 12,400, about the same as the much brighter
supergiant Rigel in Orion. From its distance of 165 light years, it shines
355 times more brightly than the Sun, from
which we find a diameter four times solar, the blue giants nowhere
near as large as their much cooler red counterparts. Though an
evolved giant, the star, about four times as massive as the Sun, is
still close to the "main sequence," and is either in the very last
stages of core hydrogen fusion or the fusion has stopped
altogether, the helium core now in a state of contraction. Over
the next few million years, Gienah will become a red giant.
Gienah's odd chemical composition separates it from the more
ordinary "blue giants," the star a member of the class of "mercury-
manganese" stars, the brightest of which is Alpheratz in Andromeda. The mercury-manganese stars have hugely
elevated levels of these and other elements, mercury up to 100,000
times normal, while having depletions of others, such as aluminum
and nickel. These chemical peculiarities are the result of the
physical separation of different kinds of atoms in the stellar
atmosphere, some sinking down through gravity, others lofted up by
radiation. Gienah was only fairly recently discovered to be such
a star because its rather rapid rotation speed of 150 kilometers
per second obscures its spectrum.