ALPHA APS (Alpha Apodis). One of the closest constellations to the
South Celestial Pole (which is held by
its neighbor, Octans), Apus (the Bird of
Paradise) is also one of the smaller and more obscure. Its
luminary (brightest star), Alpha Apodis, shines at a mere fourth
magnitude (3.83) as do Gamma (3.89), double Delta (4.18), and Beta
(4.24), not much for something as seemingly glorious as a Bird of
Paradise. The obscurity is epitomized by Alpha Aps itself, as it
has only barely made a mark on the astronomical literature. Though
clearly a giant, even the
class K spectral subclass (nominally K2.5) is uncertain, others
claiming it to be as cool as K5. If the warmer K2.5, the star is
too "red" for its class, which can be explained by up to 0.7
magnitudes of interstellar dust absorption, which is high and
unrealistic for a distance of 410 light years. If at the cooler
K5, the absorption is unneeded and goes away. A stated temperature
of 4256 puts the star nearer the warmer class (the cooler would be
4100). If truly a K2.5 giant but with no dust absorption, the star
radiates with a luminosity of 750 times that of the Sun, giving a radius 49 solar. If at the
cooler end of the scale, the luminosity and radius climb to 910 and
60 suns, while if we go back to the warmer end and add the
unrealistic 0.74 magnitudes of dust absorption, we get 1480 and 70
(which are surely too high). Clearly, the star needs a lot more
work, though given the common class, it's unlikely to get it.
Whatever the details, Apus's chief star is a more-or-less ordinary
core-helium-fusing "clump" giant (so-called because so many other
stars have similar temperatures and luminosities) with a birth mass
between four (no interstellar absorption) and five (the maximum
amount) times that of the Sun, one that began life as a hot blue
dwarf of around class B5. It will eventually lose its inert outer
hydrogen envelope and turn into a white dwarf (the remnant
nuclear core) with a mass around 0.8 times that of the Sun.
Written by Jim Kaler 4/06/07. Return to STARS.