ALPHA PYX (Alpha Pyxidis). If there were no attempt made to highlight all the sky's constellations with their brightest stars, or even their Alpha stars (which are not always one and the same), Alpha Pyx would likely never be paid much attention. This fourth magnitude (but nearly third, 3.68) star is almost lost above the bright stars of Vela, the Sails. Not in an ancient constellation, but in the modern one of Pyxis (the Compass, or Mariner's Compass), Alpha Pyx is honored by no proper name. It is, however, the luminary of its otherwise drab figure, though not by terribly much. The star is dim because it is so far away, some 850 light years, which diminishes the light of a quite luminous body. At that distance, and near the Milky Way, Alpha Pyx is also subject to a bit (about 30 percent) of dimming by the pervasive dust of interstellar space. Were the dust not in the way, the star would indeed appear at third magnitude (a respectable 3.31). Like many of the stars of neighboring Argo, Alpha Pyx is a hot, blue-white class B (B1.5) giant with an impressive surface temperature of 22,900 Kelvin. The distance and apparent magnitude, coupled with corrections for dust absorption and for a great deal of invisible ultraviolet light, yield a luminosity nearly 18,000 times that of the Sun and a diameter of 8 times solar. While called a giant, the luminosity and temperature conspire to suggest that the star is really still a hydrogen-fusing 11-solar-mass dwarf, but one that will soon begin to evolve as the interior hydrogen is all turned to helium. Born less than 18 million years ago, it seems to be involved in a circumstellar shell, and may be a member of the Beta Cephei class of multi-periodic variables (though no one quite knows for sure). Like many class B stars near the Sun, Alpha Pyx has a subsolar metal composition, its iron content about 60 percent solar, the other elements similar. Most likely, the Sun is a bit richer in metals than its local surroundings, a gift from the long lost solar birthplace.
Written by Jim Kaler. Return to STARS.