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.