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.