GORGONEA SECUNDA (Pi Persei). It's rather odd to see a fifth magnitude star (though at 4.70 on the bright side) with a proper name. But not when we look at its surroundings. Perseus, who rescued Andromeda, is known for its many massive, hot, blue stars, the Alpha Persei Cluster that surrounds and includes the constellation's luminary, the striking young Double Cluster, and perhaps topping them all, Algol, Beta Persei, the Demon Star that represents Medusa, the hideous gorgon (one look turns you to stone) slain by the famed Hero. Traditionally there were three gorgons. In Perseus there are four (mythology seemingly quite flexible), as three others hover to the south made of a close triangle of fainter stars, the second (Gorgonea Secunda), third (Gorgonea Tertia), and the fourth (Gorgonea Quarta), which are much better known by their Greek letter names as Pi, Rho, and Omega Persei (Algol also Gorgonea Prima). Oddly, they are all about the same brightness and distance, Pi Per 310 light years away (with an uncertainty of 8), Rho and Omega Per at a distance of 308 and 288 light years. Though they at first might seem to be related as some kind of a spread-out cluster, they have nothing to do with one another, as their motions are wildly different, their placement from Earth merely a coincidence. They are also very different kinds of stars, our Pi Per a class A (A2) dwarf, Rho an M4 bright giant, and Omega a common K1 giant. Focusing back on Pi, it could certainly use more work. Published temperatures range from 8180 to 9290, with an uncertain mean of 8700, which is a bit low for an A2 dwarf. Given most of the light in the visual spectrum, with distance we find a luminosity of 96 times that of the Sun and a radius of 4.3 times solar The star could either be a failing dwarf (about to give up core hydrogen fusing) with a mass of 2.7 Suns or a "failed" subgiant of 2.5 solar masses. It will before long turn into a helium-fusing giant not dissimilar to Omega Per. Pi Persei's one outstanding feature is its rapid spin of at least 177 kilometers per second at the equator, giving a rotation period of under 1.2 days. The rotation rate is enough to keep the atmospheric gases stirred up so as to prevent abundance anomalies caused by gravitational sinking of some and radiative lofting of others. While not related to Pi Per (which has no known companions), the other two gorgons would present quite a sight to anyone looking from Pi.

Written byJim Kaler11/21/14. Return to STARS.