ADHAFERA (Zeta Leonis). The Sickle of Leo
is known for the bright star Regulus and
the famous double Algieba. Just above
Algieba, you can admire a fainter star, third magnitude (but just
barely so, 3.44) Adhafera. The name, which comes directly from
Arabic and means "the lock of hair," makes sense, as the star lies
in Leo's great mane. Unfortunately, however, "Adhafera" actually
refers to nearby Coma Berenices
(Berenices Hair), and was given to Leo's star in error, a common
failing of those who applied star names. Adhafera, a yellow-white
class F (F0) giant star 260 light years away, actually shines 207
times more brightly than does the Sun. With
a temperature of 7030 Kelvin, almost all of its radiation pours out in
the visible, where we can see it (that is, there is almost no
correction for invisible ultraviolet or infrared, quite like our
Sun), from which we find a radius 10 times solar. Spinning with an
equatorial velocity of 84 kilometers per second (48 times solar),
this three solar mass star takes less than six days to make a full
rotation. Adhafera's real interest lies in its very clean state of
evolution. Class F giants are rare, as they are making a
remarkably fast transition from the main sequence (where they once
fused hydrogen to helium in their cores) to the giant state (where
they will eventually fuse helium to carbon). Only a million years
ago, Adhafera was a white class A (almost class B) dwarf. Now with
a shrinking, dead helium core, it will become an orange class K
giant star in only another million years, and will then make its
"run to the top," taking a leisurely 100 million years to expand
from 12 solar radii to a red class M giant with a radius near
that of the Earth's orbit! At that point, it will fire up its
helium and settle down for a time again as a smaller orange giant.
Also called 36 Leonis, Adhafera has a sixth magnitude "companion"
(35 Leonis) 5 minutes of arc away. Alas, it is just a line of
sight coincidence, 35 Leonis being only 100 light years away, less
than half Adhafera's distance, the two moreover going in different
directions. The fainter star is not without its interest, however.
A class G (G1.5) dwarf-subgiant, 35 Leonis has the same surface
temperature and color as does the Sun. Just beginning its
evolution to the giant state, it is more massive and 3.5 times as
luminous.