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.