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DSCHUBBA
(Delta Scorpii). The middle star of the three-star line that makes the head of Scorpius, the Scorpion, Dschubba appears just south of somewhat fainter Graffias. The name derives from an Arabic phrase meaning "the forehead" ("jabhat") of the Scorpion, which was originally applied to the whole line, Graffias, Dschubba, and somewhat fainter Pi Scorpii (which in spite of its brightness has no proper name, the downside of being in a constellation with so many bright stars). Dschubba received Bayer's Delta designation, and in fifth place it is close to the mark, but beat out not by Beta (Graffias) and Gamma, but by Lambda (Shaula), Theta, Epsilon, and of course Antares. Dschubba, a bright second magnitude star (2.32) 400 light years away, is remarkable for its complexity, and is most likely quadruple. The main component is a hot class B star (almost but not quite class O) 14,000 times brighter (including the invisible ultraviolet radiation) than the Sun and 5 times as large. It is accompanied by a cooler class B companion about ten times fainter, the two separated by roughly Mercury's distance from the Sun and taking 20 days to orbit. A third companion two-thirds as bright as the dominant star lies much farther away from it, at least at Saturn's distance, and takes at least a decade to make the trip. At a minimum double that distance lies yet another fainter star. With masses that range from 12 down to 6 times that of the Sun, all are probably still fusing hydrogen into helium in their cores. The biggest one near the center will die first and may someday look something like Antares does today. It will produce either a very heavy oxygen-neon white dwarf or will explode sometime within the next 10 to 15 million years. The others will follow in their evolution shortly thereafter, the two fainter becoming heavy, but more ordinary carbon white dwarfs (rather like Sirius-B is today). Dschubba is part of an association of O and B stars that includes both Graffias and Antares, all of which were born within the same complex of interstellar gas and dust. Dschubba is hot enough to ionize the surrounding interstellar gas out to a distance of almost 10 light years. Although fairly close to us, there is so much dust in the line of sight that the stars of Dschubba are dimmed by about fifty percent.