GAMMA LEP (Gamma Leporis). Barely fourth magnitude (3.50) Gamma Leporis, which ranks not third on Lepus the Hare's brightness scale, but fifth (even after Mu Lep), once had a name, or at least part of one, "Nihal" (from the Arabic "al- nihal," "the Camels Beginning to Quench their Thirst"), which applied to Alpha (Arneb), Beta, Gamma, and Delta, the four stars together making a prominent square. Sadly for Gamma, the name eventually went to Beta alone, leaving it with only a Greek letter. But here, we get not one star, but two, each bright enough to be visible to the naked eye, fourth- magnitude (3.60) Gamma A and sixth magnitude (6.15) Gamma B. With a separation of 97 seconds of arc, which is just above the perfect eye's resolution limit, the pair is technically a "naked-eye double." But since they are more than twice as close as those that make famed Epsilon Lyrae, don't even try to separate them without binoculars or a small telescope. Earlier astronomers called them "light yellow and pale green," a product of the eye, not the stars, which seen alone would be near-white and perhaps yellow-orange. Tracking each other through space for the past two centuries, they clearly belong together. (Gamma B has a distant "companion" called Gamma C, but it clearly just lies along the line of sight.) With Gamma A a class F (F6) hydrogen-fusing dwarf and Gamma B a K (K2) dwarf, the two quite nicely bracket the physical properties of the Sun. With a surface temperature of 6440 Kelvin (as opposed to solar 5780), Gamma Lep A glows with 2.3 times the solar luminosity, while Gamma Lep B (5000 Kelvin) comes in at a much weaker 0.29 solar luminosities, which lead to respective masses of 1.25 and 0.83 solar. The system is young, under a billion years old. With an equatorial spin speed of at least 11 kilometers per second, "A" takes under 5.6 days to make a full rotation. More focus has been on "B," however. We can see a slight and subtle variation as sunlike magnetically active areas go on and out of view, leading to an actual rotation period of 17 days. "B" seems also to emit some infrared radiation from a weak surrounding disk. The angular separation leads to a physical one of at least 870 Astronomical Units, hence to an orbital period of at least 18,000 years. At that distance, from Gamma Lep A, Gamma Lep B would shine with the light of quarter Moon, while from "B," "A" would glow with the full Moon's brightness.
Written by Jim Kaler 2/15/08. Return to STARS.