BATEN KAITOS (Zeta Ceti). Four named stars
define the main figure of Cetus, the
Sea Monster, or Whale: Menkar in his
head, the great variable Mira in his
neck, Deneb Kaitos, which marks
his tail, and Baten Kaitos, which links the long neck to the body.
Of these Baten Kaitos is the faintest, excepting of course when
Mira is on the down-side of its huge variability. At the bright
end of fourth magnitude (3.73) and seventh brightest in this large
but relatively dim constellation, the star consistently received
the Zeta designation from Bayer. The name, appropriate to the
star's position, comes directly from a two-word Arabic phrase
meaning the "sea monster's belly." Like so many stars that make
our constellations, Baten Kaitos is an orange "class K" giant with
(being on the warm side of its class) a color and temperature (4600
Kelvin) similar to much brighter
Pollux. At a distance of 260 light
years, this star shines 260 times more brightly (including its
infrared radiation) than the Sun, from
which we calculate a radius 25 times solar as befitting a true
giant. Its spectrum shows it to be accompanied by a smaller star
of unknown nature that orbits it with a period of 4.5 years and
that is separated from it by about Jupiter's distance from the Sun.
A dying star of around 2.5 solar masses, Baten Kaitos now appears
to be fusing helium into carbon in its deep core. It has been
listed as a mild "barium star," one (like Alphard) with an overabundance of the
element barium (as well as overabundances of some others). Such
stars do not come by their odd abundances on their own, but have
been contaminated by matter that flowed onto them from now-dead
companions whose own nuclear processes had grossly changed THEIR
own abundances when THEY were giants. Baten Kaitos's observed
companion seems too far away for that, however. In Baten Kaitos's
case the barium effect is so minimal that the star was quite likely
misclassified. Otherwise, its chemical composition is fairly
normal, the iron abundance about three-fourths that of the Sun.
Since the Sun appears rather high in metals for its position within
the Galaxy, Baten Kaitos fits right in with its stellar
surroundings. Baten Kaitos serves to highlight the immense
differences among stars even of the same class. Oddly, its
constellation-mate Deneb Kaitos, with which it also shares part of
a name, is also a class K giant with almost the same temperature
yet a luminosity only about half as great. Deneb Kaitos, however,
is a strong X-ray source, whereas Baten Kaitos is not. Shedar (Alpha Cassiopeiae), on the other
hand, is over three times as bright as Baten Kaitos. The
differences are caused by differences in mass and in the state of
evolution, which over millions of years can cause changes of a
factor of 1000 in the luminosities of dying stars.