ALPHA RET (Alpha Reticuli). Though shining at relatively prominent
third magnitude (3.35), and the luminary of the modern
constellation Reticulum (the Net), Alpha
Reticuli is largely ignored by the research community since the
great majority of astronomers are in the northern hemisphere where
they cannot see it, the star easily visible only from south of the
Tropic of Cancer. If in the northern hemisphere, Alpha Ret would
be a common star within most statistical data bases (and probably
would have had an "ancient" proper name). Lying at a distance of
163 light years, Alpha Ret is a yellow class G (G8) "bright giant," that is, is somewhat on
the bright side even for a giant star. Radiating at a luminosity
of 237 Suns from its coolish 4940 Kelvin surface, the star has a
giant's radius 21 times that of the Sun, and
has a rotation period slow enough that it has never been measured
(with an upper limit of 130 days). It does, however, radiate X-
rays, which shows magnetic activity likely induced by rotation.
Alpha Ret's temperature and luminosity together with the theory of
stellar structure suggest a mass 3.5 times that of the Sun. A
rather standard "clump giant" (a star that quietly fuses its helium
into carbon and oxygen), only 300 million years ago it was a
luminous blue class B star. Upon burning up the rest of its
internal helium, it will undergo a great brightening phase and then
pop its external envelope as it prepares to become a white dwarf. Unless it is
torn away by the gravity of passing stars, all this action will
continue to be witnessed by a small twelfth magnitude class M0
dwarf companion. Over the past 150 years, the little one has kept
the same motion as the big one, showing that the two really are
mated and not just a line of sight coincidence. (Technically, they
are a called a "common proper motion" pair, "proper motion" being
the movement of the star against the distant background.) The
separation of 49 seconds of arc translates into a minimum physical
separation of 2450 Astronomical Units and an orbital period of at
least 60,000 years. At this distance, from Alpha Ret proper the
companion would glow 4 or so times our Venus at maximum, while from
the companion, Alpha Ret would shine with the light of 15 full
Moons.