KAKKAB (Alpha Lupi). Don't take the proper name too seriously: it's only partial and no one ever uses it anyway. According to R. H. Allen, the full name, apparently from the ancient Euphrates Valley, is "Kakkab Su-gub Gud-Elim," meaning "the Star Left of the Horned Bull" (Centaurus). Far better to know it by its Greek letter name Alpha Lupi (the luminary of Lupus, the Wolf). This blue-white second magnitude (2.30) star lies in one of the most southerly of all the ancient constellations. Shining south of Scorpius, the figure is hardly known in the north, but from southern latitudes it is glorious, Alpha Lupi bright even though 550 light years away. A hot, class B (B1.5) giant, Alpha Lupi pours 21,000 solar luminosities (corrected for a bit of interstellar dust absorption, and most of it in the invisible ultraviolet) into space from a 21,600 Kelvin surface with a radius over 10 times that of the Sun. Like a great many hot O and B stars, "Kakkab" is a member of a loosely organized grouping, an "OB association." Huge numbers of them flock the Galaxy. Alpha Lupi is a member of the subassociation "Upper Centaurus- Lupus," or UCL, which in turn is a part of a huge super-collection called the Scorpius-Centaurus Association. From analysis of all its members, UCL lies at an average distance of 450 light years, which fits in very nicely with our star's individually measured distance of 550. As are many hot class B giants, Alpha Lupi is a "Beta Cephei star," one exemplified by Mirzam, Beta Canis Majoris. These are all subtle variables that pulsate with multiple periods. With a major oscillation cycle of 0.259847 days (the periods really known to such accuracy, to the fraction of a second), in which it varies by only 0.03 magnitudes (about 3 percent), Alpha Lupi has one of the longest periods of its class. A secondary pulsation takes 0.236798 days. A 13th magnitude "companion" 28 seconds of arc away may belong to Kakkab or may just be in the line of sight. As a spectrally-classed giant star, Alpha Lupi has probably just ceased its core hydrogen fusion. At 10 to 11 solar masses, the star -- a mere 20 million years old -- is just on the dividing line of those that will blow up as supernovae and those that will turn into massive neon-oxygen white dwarfs.
Written by Jim Kaler. Return to STARS.