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.