GAMMA VOL (Gamma Volantis). Though deemed "obscure" from the northern hemisphere, Volans (the Flying Fish) is one of the fainter mainstays of the southern, as it is close enough to the southern pole to be circumpolar from roughly the Tropic of Capricorn and south. It is an attractive kite-shaped figure whose main stars are all so much about the same brightness that it is hard to tell which is the luminary. The prize, such as it is, goes to just-barely-fourth magnitude (3.60) Gamma Volantis, which is a bit of a cheat, since the star is a wide double (separation now 14.1 seconds of arc) made of Gamma-1 Vol (the western one, at magnitude 5.67) and Gamma-2 (the eastern, at 3.78). If taken separately, Beta Vol is the winner (as stated by Allen in his "star names" book). But the pair is inseparable by the naked eye, and they add together to beat out Beta. Alpha comes in at number 3. Taken in order of brightness, Gamma-2 and Gamma-1 are respectively a rather standard orange class K (K0) giant of the kind that makes so much of our constellation patterns and a white class F (F2) dwarf, the color contrast making them an attractive pair. There are no temperature measures of either one, but from their spectral classes they should be (in the same order) 4700 and 7000 Kelvin. From the distance of 142 light years, they shine at respective luminosities of 71 and 7.9 times that of the Sun, which give radii of 12.8 and 1.9 solar and masses of 2.5 and 1.6 solar. Direct measure of angular diameter of Gamma-2 yields a radius 12.7 solar, right on the mark. Gamma-1 is an ordinary hydrogen fusing dwarf, while Gamma-2 is a stable helium fusing "clump" giant (as it is clumped in characteristics with so many other stars). The age of the system falls between 600 and 700 million years. Not for another 1.5 billion years will Gamma-1 make the break to become a giant like its larger companion, by which time Gamma-2 will have become a small white dwarf. Gamma-1 was suspected of being a spectroscopic binary, but is more likely a slightly unstable pulsating variable, a condition that affects a number of dwarfs in this temperature range. While some orbital motion is detected (the two have become 1.6 seconds of arc closer over the past 150 or so years), there is nowhere enough information to construct the actual orbit. Given the projected separation of 600 Astronomical Units and the estimated masses, the orbital period must be at least 7500 years. At the projected distance, from Gamma-2, Gamma-1 would shine at about the brightness of our full Moon, while from Gamma-1, Gamma-2 would be nearly 6 times brighter. (That the total luminosity ratio is greater is the result of taking invisible infrared radiation from Gamma-2 into account.)
Written by Jim Kaler. Return to STARS.