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KAPPA SCO (Kappa Scorpii). The curves of stars that make the bodyofScorpius, the Scorpion, is one of themost dramatic and recognizable figures of the nightly sky. At thesoutheastern end, just short of the two-star "stinger" (made ofShaula andLesath)lies bright, second magnitude (2.41) Kappa Scorpii, which if inmost other constellations would bear a proper name, but here tendsto be lost among the host of other bright stars. And too bad,because this class B (B1.5)giant has a double surprise: it'sboth binary, with a lesser companion, at the same time that thedominant star is a subtleBeta Cephei-type variable. At a rather large measured distance of 465 lightyears (enough for about a ten percent dimming due to interstellardust), the two together radiate a hefty energy of 15,300Suns. Spectroscopic analysis and orbit (knownfrom the shifts in the wavelengths of the stars' light) givesindividual temperatures of 23,400 and 18,800 Kelvin for the KappaSco A and Kappa Sco B (making the latter a mid-class B star), plusradii of 6.8 and 5.8 solar and an estimate for individualluminosities that lead to 11,700 Suns for the primary star and 3550for the lesser, from which in turn we derive masses of 10.5 and 7solar (published masses are even higher). With a measured orbitalperiod of 195.65 days (0.536 years), the two must be separated by1.7 Astronomical Units, a bit farther than Mars is from the Sun. A rather high orbital eccentricity takes them from 2.5 AU apart toonly 0.87 AU, less than the Earth's orbital size. The moremassive, Kappa Sco A, falls nicely into the realm of theBeta Cephei class of stars, oscillating overonly three hundredths of a magnitude with multiple periods of0.200, 0.205, 7.3. 0.19, and 2.59 days, some parts of the starmoving outward, while others move inward. Kappa Sco's metalcontent is (typical of class B stars) 65 percent that of the Sun,while it spins (the two unrelated) with a typical equatorialvelocity of at least 130 kilometers per second (giving a rotationperiod of under 2.5 days). The star is assumed to be part of thehuge Scorpius-Centaurus association ofhot blue stars, though its membership is not confirmed. Both areat the ends of their hydrogen-fusing lives. The larger of the twomay be big enough to explode as asupernova, while the lesserwill become a massivewhitedwarf. Such an explosion may even eject Kappa Sco B from thesystem, creating a "runaway star" likeZeta Ophiuchi.
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