KAPPA PSC (Kappa Piscium). While relatively faint, the Circlet of Pisces, lying just northwest of
the Vernal Equinox, is among the sky's
most beloved figures. Its brightest star, Gamma Psc, is fourth magnitude (3.69),
while Kappa Piscium (the Circlet's southernmost star), is but mid-
fifth (4.94). Something of an "equator star," it resides but 1.3
degrees north of the celestial equator. As a result of precession it is being pushed to the
north, and crossed over from the southern hemisphere in 1771.
While it looks as if it might be a visual double with sixth
magnitude 9 Psc (Kappa also 8 Psc) just 10 minutes of arc to the
southeast, the two are not related. Kappa is a peculiar class A
(A0p) dwarf at a distance of 162 light years, while 9 Psc is a
glass G7 giant 2.5 times farther away. Numerous determinations of
temperature give Kappa an average of 9225 Kelvin, cool for a class
A0 star, which is probably the result of mis-classifying stars with
odd spectra that result from strange chemical abundances. After a
small correction for ultraviolet light, the magnitude and distance
yield a luminosity 23 times that of the Sun,
a radius of 1.9 solar, a mass 2.1 solar, and an age of 370 million
years, just 37 percent of its billion-year hydrogen-fusing
lifetime. It is, of course, the peculiar chemistry that makes the
little one stand out, in addition to a magnetic personality. Kappa
Psc is classed as an "Alpha-2 CVn star" after the prototype, Cor Caroli in Canes
Venatici. Most are class A stars that possess strong magnetic
fields that are inclined to their rotation axes. Diffusion of
elements coupled with magnetic spots produce enormous enhancements
of chromium, silicon, and rare earths (in this case strontium) that
swing in and out of the line of sight as the star rotates, allowing
for a measure of rotation period. The spottedness produces
brightness variations between magnitudes 4.91 and 4.96. Kappa's
field averages about 300 times that of Earth's, with a wide
variability that takes it to 1000 Earth-fields. The rotation
period, however is ambiguous, with measures of 0.58, 1.14, and 1.42
days, the longest seeming to be the correct one. A measured
rotation velocity of 40 kilometers per second gives an upper limit
to the rotation period of 2.3 day, from which, with the longer true
period, gives an axial tilt of 37 degrees to the plane of the sky
and a true rotation speed of 66 km/s. Hanging out in the area are
two "companions," Kappa-B, a 12th magnitude star 175 seconds away
from the main star, and Kappa-C, a 13th magnitude star 76 seconds
from Kappa B. Neither belongs, as both just line of sight
coincidences.
Written by Jim Kaler 11/09/07. Return to STARS.