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.