ZAURAK (Gamma Eridani). Sounding something like the name of a commander of a starfleet battleship, "Zaurak" (directly out of Arabic) actually does mean "boat." It is just the sort of star you would expect to find floating in Eridanus, the dim but ancient celestial river. The name was originally applied to other stars near the river, particularly to the stars of the modern constellation Phoenix (near Achernar in southern Eridanus). But the name was reassigned, and now the boat is represented by a star smack in the middle of northern Eridanus, the part that flows more or less westward before it takes its plunge to the deep south. At mid-third magnitude (2.95), it is the third brightest star in the constellation, right behind Cursa (Orion's famed "footstool"), and following Bayer's basic rule received his gamma designation. To find it, follow the bottom two stars of Orion about twice their separation to the right and then drop down. Zaurak is unusual for at least a couple reasons. It is one of the sky's rare visually bright red giants of class M (M0.5). Its closest match is probably Yed Prior in Ophiuchus. Near the warm edge of the class, its surface shines with a temperature of 3850 Kelvin. From that and its distance of 221 light years (about 30% farther than Yed Prior) we find a luminosity (accounting for invisible infrared radiation) 860 times that of the Sun, which requires a radius 66 times solar, or about 80% the size of Mercury's orbit. Oddly, and perhaps the most unusual thing about Zaurak (other than a fairly high velocity relative to the Sun), is the lack of attention paid to it. The star must be one of the least-studied of the cooler bright stars. The reason seems to be its quiet nature and (other than that it is in the act of dying) its rather perfect normality. It has no known companions (a star lying near it just being in the line of sight), and aside from a small erratic brightness variation of around three percent, it does not do anything but stare back at us. Its very normality, however, makes it a fine "comparison star," with which to study other stars of stranger nature. Normality aside, its real condition remains mysterious. With a very uncertain mass perhaps twice that of the Sun, it ceased its hydrogen fusion a billion-plus years ago. It may now be just ready to fuse its internal helium to carbon, or more likely, it may already have quit that stage and (with a carbon-oxygen core) is preparing itself to become a much larger and cooler giant like Mira.
Written by Jim Kaler 1/14/99. Return to STARS.