DSCHUBBA (Delta Scorpii). The middle star of the three-star line that makes the head of Scorpius, the Scorpion, Dschubba appears just south of (usually) 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, usually a bright second magnitude star (previously measured at 2.32) that is 400 light years away, underwent a remarkable change. In July 2000, the star began to brighten, and during 2001 and 2002 began to close in on first magnitude as it turned itself into a "B-emission" star rather like Gamma Cassiopeiae, one with a surrounding disk produced in part by rapid rotation (which is at least 181 kilometers per second at the equator, 90 times that of the Sun).
Dschubba The visual light curve of Dschubba, Delta Scorpii, is plotted against Julian Date. JD 2451750 is July 24, 2000, JD 2454000 September 21, 2006. The black points are visual estimates, the green ones photoelectric measures. Delta Sco began erupting in 2000, climbed to near first magnitude as it developed a surrounding disk, and has not yet returned to normal. Courtesy of the American Association of Variable Star Observers (AAVSO).
Dschubba received Bayer's Delta designation, and originally in fifth place in brightness it is close to the mark, but beat out not by Beta (Graffias), but by Lambda (Shaula), Theta, Epsilon, and of course Antares. At its peak in 2003-2004, the star was number two in the constellation right after Antares itself. As of 2008,it remains in an erratic semi-high state near magnitude 2.1, about 0.2 magnitudes brighter than normal. Dschubba is also remarkable for its complexity, and is most likely quadruple. The main component, the one that is brightening, is a hot class B (B0) star (almost but not quite class O) at least 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 over 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 was originally 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 (though the main component, a "subgiant," may be close or even beyond the end of that stage.) The main component 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 as a supernova. 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. (Thanks to the American Association of Variable Star Observers.)
Written by Jim Kaler 3/28/02; updated 7/25/08. Return to STARS.