RANA (Delta Eridani). In the middle of the western flow of Eridanus, the River, just to the east of Epsilon Eridani, lies the star Rana. Star names are sometimes a confusing mess. "Rana" seems to have been erroneously transferred in the 20th century from the Latinized version of an alternative name for Deneb Kaitos, "Rana Secunda," which means (from old Arabic culture) the "second frog" (Fomalhaut being the "first frog"). Better to call the star by its Greek letter name, Delta Eridani, though this barely fourth magnitude (3.54) star is actually the fifth brightest in the celestial stream. The star itself has a bit of confusion about it too, as it is listed as an "RS Canum Venaticorum" variable like Lambda Andromedae (in which a pair of stars orbit closely, making one of them more magnetically active than normal), which it almost certainly is not. It is active however. Rana is a class K (K0) subgiant, a star that has recently given up its core hydrogen fusion. It is quite close to us, only 30 light years away, and shines but with a luminosity of 3.3 times that of the Sun. Factoring in its coolish temperature of 5075 Kelvin, its radius is 2.3 times solar, and from the theory or stellar evolution its mass is just 20 percent greater than that of the Sun. Having started life as an F8 dwarf (just a bit hotter and brighter than the Sun, in accord with its slightly greater mass) 7.5 or so billion years ago, the cessation of core hydrogen fusion has caused it to expand and cool. It is now just preparing to make its run to much higher luminosity and radius as a true giant star. Magnetic activity, associated with sunspots (rather, starspots), derives from a dynamo produced by stellar rotation. In spite of the fact that Rana has slowed with age to a projected rotation period of 116 days (though in fact probably less), it does exhibit some sort of activity, from whence cometh the "RS Can Ven" label. It does not, however, exhibit any evidence for a companion. The advanced age of the star is consistent with its lithium content. Lithium is a rare chemical element that is easily destroyed by nuclear reactions in a high temperature environment. As gases of the cooler stars circulate up and down by convection, their lithium contents therefore steadily decline. While Delta Eri has an overall metal abundance 50 percent greater than that of the Sun, its lithium content is only half solar.
- - Written by Jim Kaler