GAMMA SCL (Gamma Sculptoris). Among the more well-known southern constellations visible from the mid-north is Piscis Austrinus, the Southern Fish, not from any sort of prominent configuration, but because of its singular bright star, Fomalhaut, "the Fish's Mouth," toward which Aquarius dumps his water jug. To the east of it lies a field of faint stars that in the 18th century were used by the Abbe Nicolas de Lacaille to construct the modern constellation Sculptor, the Sculptor's Studio, which is best known for containing the south pole of the Galaxy (opposite the north Galactic Pole in Coma Berenices). Sculptor's three brightest stars, Alpha, Beta, and Gamma (applied long after Bayer's time), indistinguishable in brightness to the naked eye and lettered east to west, are still in magnitude order, all fourth, Gamma of magnitude 4.41, just a tenth fainter than Alpha. It is Gamma Sculptoris, though, that rules the constellation, as it forms a notable triangle with Fomalhaut and the Gamma-Delta Piscis Austrini pair. It's almost as if the fish is lunging for Gamma with wide open mouth. Looked at another way, Gamma Scl forms the point of a prominent wedge that diverges westerly through Piscis Austrinus. Position aside, as a star, it's pretty non-extraordinary, yet another class K (K1, some say G8) helium-fusing "clump" giant (so called because on a graph of stellar luminosity against temperature, bunches of helium- fusing giant stars of different masses collect around the same place). Yet we could not do without them. Throw away the K giants and the constellation patterns would be severely altered. A temperature of 4520 Kelvin (expected for class K1), to allow for infrared radiation, and a precise distance of 182 (give or take 2) light years lead to a luminosity 74 times that of the Sun and a radius of 14 solar, a bit high for the 13 solar radii adopted as an interferometry standard. Application of the rules of stellar structure and evolution give a mass of about double that of the Sun and an age of around 1.3 billion years. Several studies of chemical composition suggest that Gamma Scl contains about three- fourths of the solar iron content (relative to hydrogen). There is no measure of rotation, and nobody has turned up any companions, so for any sort of fame, the star will have to be satisfied with that derived from its location to east of the ancient Southern Fish.
Written by Jim Kaler 11/18/11. Return to STARS.