ALPHA CAE (Alpha Caeli). Of the 38 recognized modern
constellations, those invented between about 1600 and 1800, Caelum, the Engraving Tool, is among the
dimmest, the figure (which hardly looks its name) lying southwest
of Columba, the Dove, a much finer
pattern. Consistent with its name, Alpha Caeli (no proper name) is
Caelum's brightest star, though not by much. At the low-brightness
edge of fourth magnitude (4.46), it just beats Beta Caeli by a
tenth of a magnitude. Dim as it is, however, the star has its
draw. A double star, it consists of a somewhat solar-like class F
(F2) dwarf coupled with a much fainter class M (M0.5) dwarf at the
top edge of thirteenth magnitude (12.5), the dimness and separation
of 6 seconds of arc making it a very difficult observation for the
small telescope. Fairly nearby, 66 light years away, the 7100
Kelvin brighter F star shines with the light of 5.2 Suns, the radius only 1.5 times solar.
Rotating with an equatorial speed of at least 52 kilometers per
second, the star spins with a period of at most 1.4 days, much less
than the Sun and typical of the hotter F stars that lie near (or
hotter than) the so-called "rotation break," that divides slower
rotating stars like the Sun from the faster rotating hotter ones.
Though this star -- Alpha Caeli A -- has a mass of only 1.5 solar,
it is much greater than that of the companion, Alpha Caeli B, which
weighs in at but 0.3 solar. The low mass gives "B" a miserable
luminosity of only a percent that of the Sun, this red dwarf having
a surface temperature only 3800 Kelvin. Both temperatures are
averages for stars of these classes, Alpha Cae so neglected that
they have never actually been measured. Alpha Caeli B makes up for
that by being a "flare star," one that (much like Proxima Centauri) can unpredictably brighten by a
magnitude or more as a result of the release of magnetic energy.
Alpha Caeli A may be a subtly-varying "
Delta Scuti star" rather
like much brighter Caph (Beta Cassiopeiae).
The separation of Alpha Caeli A and B is not really known. They
were 3 seconds of arc apart in 1896, 6.3 seconds in 1933, and the
binary has not been visited since! Assuming 6.3, the two are at
least 1000 Astronomical Units apart, and take at least 130 years to
orbit each other. From B, A would shine 360 times brighter than
our full Moon, while from A, B would glow redly with the light of
over 100 of our Venuses.