GRUMIUM (Xi Draconis). With a name like that, were you a star, you'd probably prefer "Xi." Allen calls this faintest (fourth magnitude, 3.75) star in the head of Draco, the Dragon, a "barbarism." Kunitzsch and Smart, on the other hand, have it derived from a Latin word meaning a pig's snout, sort of appropriate for the "serpent's jawbone." In the celestial art found on old star atlases (Bayer's Uranometria), the Dragon's body twists four times starting at the head, these "nodes" marked by four stars. The best known of them is the second, "Nodus II," also called Altais, more commonly Delta Draconis. Our Grumium, Xi Dra, marks the first twist, and is hence Nodus I. Because of the easy confusion between the lower-case Greek "Xi" and "Zeta," Zeta is occasionally erroneously tagged as Nodus I, whereas it is actually Nodus III (a term used beyond rarity). To round us out is Theta (or possibly Iota) Dra as Nodus IV. Aside from the complexity of the names, as an orange class K2 giant, Xi Dra at first seems pretty ordinary. It does, however, have its own evolutionary twist in addition to its cultural one. From a distance of 111 light years, Nodus I shines with the light of 53 Suns, not all that much for a giant star, which leads to a radius of just 12 times solar and a mass of 1.5 times that of the Sun. Born three billion years ago, instead of being a quiet helium (to carbon) burner, it seems to have recently (160 million years ago) left its hydrogen-fusing dwarfhood behind and is now brightening as a giant with a dead helium core. (Its physical state is uncertain, however. It could also already have reached its peak luminosity and be dimming after initiating helium fusion.) A 16th magnitude star 316 seconds of arc away is listed as a binary companion, but since there is only one measure, there is no way to tell if the two are tracking each other through space. Most likely, the pairing is just a line-of-sight coincidence. If they are indeed connected, then Xi Dra B would be an M6 dwarf at least 11,000 Astronomical Units away, leading to an orbital period of 800,000 years. But the companionship seems unlikely at best.
Written by Jim Kaler 8/29/08. Return to STARS.