43 CAS (43 Cassiopeiae). A few degrees north of the back of Cassiopeia's Chair (or if you wish, the eastern end of her "W"), lies a little gently curved string of four fainter stars, from east to west Omega Cas, 43 Cas, Psi Cas, and 31 Cas (the second and fourth of these being Flamsteed numbers). The first two stars, Omega and 43, show the odd chemistries that can take over in the outer layers of modestly warm stars of classes F, B, and A. Omega is a class B (B8) "helium weak" star about which little else is known. Such stars rotate slowly, which allows some chemical elements to fall under the force of gravity, while others can be lofted up via the star's radiation. A bit over a half a magnitude fainter than Omega, just a hair into sixth magnitude (5.59), 43 Cas goes Omega one better by sporting a magnetic field, rendering it an "Alpha-2 Canum Venaticorum" star. The field, for 43 Cas a few hundred times the strength of Earth's, not all that strong for the class, changes the composition even more. At a modest distance of 389 light years (give or take 23), 43 Cas seems to suffer from no dimming by interstellar dust within the Milky Way. It's listed as a class A (A0) "peculiar" (A0p) star with enhanced silicon, strontium, chromium, and europium, which can render the class somewhat ambiguous. The magnetic field forms starspots with peculiar abundances that align to a magnetic field that is tilted relative to the rotation axis. As the spots swing in and out of view, such stars vary somewhat, 43 Cas by about a tenth of a magnitude over a 3.16 day period (which must them be the star's rotation period). A temperature of 11,900 (which is more appropriate to a hotter B8 star, as is the star's color) and distance give a luminosity of 120 Suns and a radius 2.6 solar. A projected equatorial rotation velocity of 25 kilometers per second gives a rotation period of under 5.2 days. The true rotation period of 3.16 days as told by the star's variation gives a true rotation velocity of 42 km/s (consistent with the curious composition) and an axial tilt of 37 degrees to the line of sight. The theory of stellar structure and evolution then give a mass of three times that of the Sun, and show the star to be a dwarf well along toward the end of its 400 million year hydrogen fusing lifetime. There is no known companion, so 43 Cas will have to become a helium fusing giant, slough off its outer layers as an advanced giant through winds, perhaps produce a surrounding planetary nebula, and turn into a 0.7 solar mass white dwarf all by itself.

Written by Jim Kaler 10/26/12. Return to STARS.