KAPPA CAS (Kappa Cassiopeiae). Cassiopeia, the Queen, is recognized by two obvious configurations, the first her famed "W," made (from west to east) of Caph (Beta Cas), Shedar (Alpha), Gamma, Ruchbah (Delta), and Epsilon. Add fainter Kappa Cas (which has no proper name) to the "W," and you see the more classical figure, Cassiopeia's Chair: her throne. While at fourth magnitude (4.19) the faintest of the set, Kappa Cas is in reality the grandest of the Cassiopean stars, topping even Gamma Cas. The star seems dim only because of its great distance of 3500 light years and nearly a magnitude of dimming (a factor of 2.5) by interstellar dust that lies in the Milky Way along the line of sight. The very hot (24,000 Kelvin) blue class B (B1) supergiant also radiates much of its energy in the ultraviolet. Account for that, and we find an astounding luminosity 420,000 times that of the Sun! The implied radius is nearly 40 times solar, or about 20 percent the distance between the Earth and the Sun. If Kappa Cas were our Sun, for us to survive we would have to orbit at a distance 650 times farther than we are now, and our year would be 2600 current Earth-years long. Stars like this one are so large and luminous that they become somewhat unstable, Kappa Cas varying slightly by under a tenth of a magnitude. They also blow strong winds back into space. Kappa loses mass at rate of 2 millionths of a solar mass a year (over 10 million times the flow rate of the solar wind) with a wind speed of over 1000 kilometers per second. The enormous luminosity can be produced only by a star of great mass. Kappa Cas is an evolving, dying star that was born with a mass of around 40 times that of the Sun. Some 5 million years old, it is now probably fusing helium into carbon in its deep core, and has little time (on an astronomical scale) before exploding as a grand supernova. The star is on the edge of those whose central cores might actually collapse into a black hole, a body so dense that even light cannot escape. So keep your eye on the Queen and imagine her broken Chair if Kappa were to disappear.
Written by Jim Kaler. Return to STARS.