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.