KAPPA SCO (Kappa Scorpii). The curves of stars that make the body
of Scorpius, the Scorpion, is one of the
most dramatic and recognizable figures of the nightly sky. At the
southeastern end, just short of the two-star "stinger" (made of Shaula and Lesath)
lies bright, second magnitude (2.41) Kappa Scorpii, which if in
most other constellations would bear a proper name, but here tends
to be lost among the host of other bright stars. And too bad,
because this class B (B1.5) giant has a double surprise: it's
both binary, with a lesser companion, at the same time that the
dominant star is a subtle Beta Cephei-
type variable. At a rather large measured distance of 465 light
years (enough for about a ten percent dimming due to interstellar
dust), the two together radiate a hefty energy of 15,300 Suns. Spectroscopic analysis and orbit (known
from the shifts in the wavelengths of the stars' light) gives
individual temperatures of 23,400 and 18,800 Kelvin for the Kappa
Sco A and Kappa Sco B (making the latter a mid-class B star), plus
radii of 6.8 and 5.8 solar and an estimate for individual
luminosities that lead to 11,700 Suns for the primary star and 3550
for the lesser, from which in turn we derive masses of 10.5 and 7
solar (published masses are even higher). With a measured orbital
period of 195.65 days (0.536 years), the two must be separated by
1.7 Astronomical Units, a bit farther than Mars is from the Sun.
A rather high orbital eccentricity takes them from 2.5 AU apart to
only 0.87 AU, less than the Earth's orbital size. The more
massive, Kappa Sco A, falls nicely into the realm of the Beta Cephei class of stars, oscillating over
only three hundredths of a magnitude with multiple periods of
0.200, 0.205, 7.3. 0.19, and 2.59 days, some parts of the star
moving outward, while others move inward. Kappa Sco's metal
content is (typical of class B stars) 65 percent that of the Sun,
while it spins (the two unrelated) with a typical equatorial
velocity of at least 130 kilometers per second (giving a rotation
period of under 2.5 days). The star is assumed to be part of the
huge Scorpius-Centaurus association of
hot blue stars, though its membership is not confirmed. Both are
at the ends of their hydrogen-fusing lives. The larger of the two
may be big enough to explode as a supernova, while the lesser
will become a massive white
dwarf. Such an explosion may even eject Kappa Sco B from the
system, creating a "runaway star" like
Zeta Ophiuchi.