Alpha Apodis

α Apodis shines at magnitude 3.83, and is the brightest star in the small, obscure southern constellation of Apus, the Bird of Paradise. The obscurity is epitomized by α Aps itself, which has barely made a mark on the astronomical literature.

Properties

Though clearly a giant, even the spectral class of α Aps is uncertain. Nominally K2.5, some claim it to be as cool as K5. If the warmer K2.5 classification is correct, 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 the cooler K5 class is correct, the absorption is unneeded. A stated temperature of 4256 K puts the star nearer the warmer class (the cooler would be 4100).

If α Aps is truly a K2.5 giant with no dust absorption, it radiates with a luminosity of 750 times the Sun's, giving it a radius 49 times 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, work remains to be done here.

Whatever the details, Apus's chief star is a more-or-less ordinary helium-fusing giant with a birth mass between four and five times the Sun's. It began life as a hot blue dwarf around class B5. It will eventually lose its inert outer hydrogen envelope and turn into a white dwarf with a mass around 0.8 times the Sun's.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]