ALPHA ANT (Alpha Antliae). Little attention is paid this star.
Even less would be if it were not the remarkably dim luminary of an
even more obscure constellation, Antlia,
the Air Pump. It's hard to fathom that anyone would invent a
figure in which the brightest star is on the faint end of fourth
magnitude (4.28), but the nineteenth-century's Abbe Lacaille
(Antlia's inventor) did anyway. Physically, Alpha Ant appears as
an orange class K (K4) giant placed 365 light years away, which is
why it appears so dim. It is a bit on the cool side, however, and
has been classed as low as M0, showing that it is not just another
helium-burning "clump star" (one of the pack), but is a bit
different. There is some indication of the spectroscopic detection
of a binary companion, but that is most likely caused by motions in
the star's atmosphere, as it is somewhat variable, and is also
losing mass. How variable is not known, as the star has never been
the subject of a particular study -- in fact it is hardly noted at
all,less than one science paper a year mentioning it. This
isolated star provides a good example astronomers face in dealing
with the problem of stellar evolution, the ageing process. Its
state of being depends critically on both distance and temperature.
The K4 spectral class says 4100 Kelvin, while the single actual
measure, which probably no more reliable, gives 3990. The problem
is in the allowance for low-energy infrared radiation not seen by
the eye, which climbs quickly with dropping temperature. If the
higher temperature is valid, then the luminosity is 480 Suns. The formal error in the distance (the
degree to which we are uncertain about it) gives a luminosity range
of about 15 percent. If the cooler temperature is correct, then
the star shines with the brightness of 555 Suns (with the same
percentage range). The real problem is that stars with a
significant range of mass all rather look alike during the various
giant stages, allowing a range of 1.7 to 3 times that of the Sun.
One thing is sure, that Alpha Antliae is not at this moment stable.
We cannot quite tell, however, if it is brightening with a dead
helium core, dimming with helium core burning to carbon and oxygen,
or brightening with a dead carbon core. The most likely scenario
is that it is a 2.2 solar mass star that is on its "way up,"
brightening for the second time with carbon core and an age of
about a billion years (supported by its variability). It will turn
into a Mira-type variable and then pop its outer envelope to turn
into a white dwarf.