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DSCHUBBA (Delta Scorpii). The middle star of the three-star linethat makes the head ofScorpius, theScorpion, Dschubba appears just south of (usually) somewhat fainterGraffias. The name derives from an Arabic phrase meaning "theforehead" (jabhat) of the scorpion, which was originally applied tothe whole line,Graffias, Dschubba, andsomewhat fainterPi Scorpii (which inspite of its brightness has no proper name, the downside of beingin aconstellation with so many brightstars). 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 tobrighten, and during 2001 and 2002 began to close in on firstmagnitude as it turned itself into a "B-emission" star rather likeGamma Cassiopeiae, one with asurrounding disk produced in part by rapid rotation (which is atleast 181 kilometers per second at the equator, 90 times that ofthe Sun).

The visual light curve of Dschubba, Delta Scorpii, is plottedagainstJulian Date. JD 2451750 is July 24,2000, JD 2454000 September 21, 2006. The black points are visualestimates, the green ones photoelectric measures. Delta Sco beganerupting in 2000, climbed to near first magnitude as it developeda surrounding disk, and has not yet returned to normal. Courtesyof the American Association of Variable Star Observers (AAVSO).

Dschubba received Bayer's Delta designation, andoriginally 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 courseAntares. At its peak in 2003-2004, thestar was number two in the constellation right after Antares itself. As of 2008,it remains in an erratic semi-highstate near magnitude 2.1, about 0.2 magnitudes brighter than normal. Dschubba is also remarkable for its complexity, and ismost likely quadruple. The main component, the one that isbrightening, is a hot class B (B0) star (almost but not quite classO) at least 14,000 times brighter (including the invisibleultraviolet radiation) than the Sun and 5 times as large. It isaccompanied by a cooler class Bcompanion over ten timesfainter, the two separated by roughly Mercury's distance from theSun and taking 20 days to orbit. A third companion two-thirds asbright as the dominant star was originally lies much farther awayfrom it, at least at Saturn's distance, and takes at least a decadeto make the trip. At a minimum double that distance lies yetanother fainter star. With masses that range from 12 down to 6times that of the Sun, all are probably still fusing hydrogen intohelium in their cores (though the main component, a "subgiant," maybe close or even beyond the end of that stage.) The main componentwill die first and may someday look something like Antares doestoday. It will produce either a very heavy oxygen-neonwhite dwarf or will explodesometime within the next 10 to 15 million years as asupernova. The others willfollow in their evolution shortly thereafter, the two fainterbecoming heavy, but more ordinary carbon white dwarfs (rather likeSirius-B is today). Dschubba is part of an association of O and Bstars that includes both Graffias and Antares, all of which wereborn within the same complex of interstellar gas and dust. Dschubba is hot enough toionize the surrounding interstellar gasout to a distance of almost 10 light years. Although fairly closeto us, there is so much dust in the line of sight that the stars ofDschubba are dimmed by about fifty percent. (Thanks to the American Association of Variable Star Observers.)

Written byJim Kaler 3/28/02; updated7/25/08. Return toSTARS.

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