AZHA (Eta Eridani). Eridanus, the great celestial River, has its source at Cursa near Rigel, then flows more or less to the east. Suddenly, at Azha (to which Bayer gave the Greek letter Eta), Eridanus makes a sharp bend toward the south toward its first and ancient end at Acamar (Theta Eridani), then at its more modern finish at Achernar (Alpha Eridani). One might think that the word "Azha" would have something to do with the steep southerly plunge. Instead, the name comes to us as a near hopeless corruption of the name for an Arabic asterism that means "the Ostrich's Nest" and that includes a whole gang of stars (Zeta, Rho-1, Rho-2, Eta, the various "Taus," and a couple stars in nearby Cetus.) rather than just one. Azha is a classic orange class K (K1) giant star whose characteristics fall almost exactly between those of Arcturus and Pollux. At fourth magnitude (3.89) it is not nearly so well known as these two only because it is considerably farther away, 133 light years. Accounting for some infrared radiation from its 4650 Kelvin surface, the star radiates a power 59 times the Sun's, its radius 12 times solar, the mass between 1.7 and 2 times solar. Like all such orange giants, Azha is dying, its core hydrogen fuel having run out. As a "clump star," however, it is in a relatively stable period in which it is now converting its core helium into carbon and oxygen, the core surrounded by a shell of fusing hydrogen. The chemical compositions of giant stars are of considerable importance, as they tell both something of the star's birth history (and hence how the Galaxy developed) and of any internal nuclear processing whose by-products have been brought to the surface. Here there is argument, some authors seeing Azha as slightly metal- deficient, others as a bit metal-rich, the average being close to solar. There is some slight evidence that even-numbered chemical elements are a bit high relative to what is found in the Sun, suggesting that Azha has a somewhat different heritage than does the Sun (as do most of the nearby stars). Azha has also been listed as a "mild" or "semi" barium star. Such stars have not enriched themselves, but aeons ago were enriched in heavy elements through mass transfer from a more massive companion that is now a white dwarf. The seeming barium enrichment is so small, however, that it is probably a false reading, and no companions at all are detected, the star remaining a near-perfect paradigm of its class.
Written by Jim Kaler. Return to STARS.