Edasich (Iota Draconis)

(The Planet Project)


The upper circle shows the location of the class K2 giant star Iota Draconis, also known as Edasich (in the constellation Draco). Iota Draconis is the first giant with a confirmed substellar companion. The companion has a large lower mass limit of 8.9 times the mass of Jupiter in a relatively large elliptical orbit of 1.3 Astronomical Units (195 million kilometers, 120 million miles), 30 percent larger than the orbit of the Earth. During its "year" of 536 days (1.47 Earth years), the high eccentricity takes the small body from a maximum distance of 2.1 AU to a minimum of 0.39 AU and back again, which would make inner planets impossible. The unknown orbital tilt or inclination makes it impossible to know how high the mass of the small body really is. The high lower mass limit consequently makes it quite possible that the companion to Iota Draconis might be a brown dwarf rather than a planet. (Brown dwarfs are substars that are not massive enough to run full fusion in their cores, while planets are built up from dusty leftover disks the circulate around new stars.)


Edasich (Iota Draconis) is but one of two planet-hosting stars that have proper names, the other Errai (Gamma Cephei). "Edasich" is a corruption of an Arabic term that means "the male hyena." Iota Draconis is an easily visible third magnitude (3.31) class K (K2) orange giant star in Draco's tail not far in the sky from Thuban that lies only 102 light years away. Iota Dra is the first giant star known to have a substellar companion. From its 4490 Kelvin surface, it radiates 70 solar luminosities into space, and is most-likely brightening with a dead helium core. With a mass of only 1.05 times that of the Sun, Iota Draconis gives us a vision of what will happen to the Sun in another 6 or so billion years. Though most stars with planets appear to be significantly metal-rich, the metal content of Iota Draconis is close to solar. A ninth magnitude "companion" star some four minutes of arc away seems now to be just a line of sight coincidence.

HR 6817 Draconis, the lower circled star, also has an orbiting planet.