Gamma Eridani - Zaurak

At magnitude 2.95, Gamma Eridani or Zaurak is the third brightest star in the constellation Eridanus, the River. Sounding like the name of a starfleet battleship, "Zaurak" (from the Arabic "Az-Zawraq") actually does mean "boat." The name was originally applied to other stars near the River, but was reassigned to γ Eri, which lies smack in the middle of northern Eridanus. The USS Zaurak (AK-117) was a cargo ship commissioned in 1943 by the U.S. Navy for service in World War II.

Properties

Zaurak is unusual for a couple of reasons. It is one of the sky's rare, visually bright red giants of class M; more specifically, M0.5IIICa-ICr -. Near the warm edge of class M, its surface has a temperature of 3850 K. From that, and from its distance of 220 light years, its luminosity is 860 times the Sun's, which implies a radius 66 times solar. It has no known companions, other than a nearby star in the same line of sight, and a small erratic brightness variation of around 3%. With a very uncertain mass perhaps twice the Sun's, it ceased fusing hydrogen a billion-plus years ago. It may now be fusing its internal helium to carbon and oxygen; or more likely, it may already have finished that stage and is preparing to become a much larger and cooler giant, like Mira.

Zaurak is one of the least-studied of the cooler bright giants. Its very normality makes it a fine "standard star," against which to compare other stars of stranger nature.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]