GAMMA PSC (Gamma Piscium). Pisces, the
Fishes, the constellation that contains the Vernal Equinox, is oddly nearly devoid of proper names,
only Alpha (Alrescha) and Eta (Kullat Nunu) getting them. A bit odder
still, the brightest star in the figure is Eta, while Alpha is
number three. In between is nameless Gamma, which shines to us
from just over the fourth magnitude line (3.69). Outwardly, it is
just another yellow-orange giant at the warm end of class K (K0) or
the cool end of neighboring class G (G9), the temperature of 4833
Kelvin more supporting the latter. From a distance of 130 light
years, the star shines (accounting for some infrared radiation)
only with the light of 61 Suns, not all that
much for a giant, the radius a mere 11 solar. The reason is that
two-solar-mass Gamma Psc is rather at the bottom of its gianthood,
resting so to speak, while it fuses the last part of its internal
helium core into carbon. Once upon a time a white class A (about
A2) star with a current age of 1.4 billion years, Gamma Psc is
preparing to make a run toward much greater luminosity and size,
when it will eventually slough off its outer envelope and turn into
white dwarf. What rather dramatically distinguishes the star is
its speed. While the spectrograph shows it to be approaching us at
a modest 14 kilometers per second, observation of its motion ACROSS
the sky reveals it to be moving to the east at over three-quarters
of a second of arc per year, which at 130 light years corresponds
to 145 kilometers per second, over 7 times faster than most local
stars. Its speed reveals that Gamma Piscium is a visitor from a
another part of the Galaxy, from outside the thin disk of stars
that makes the Milky Way and that includes the Sun. Such stars are
commonly somewhat low in metal content, as they were formed in a
region in which exploding stars did not have sufficient time to
build up the amounts of iron and other elements that we see in the
thin disk. And sure enough, Gamma's metal content is low, only
about a quarter that of the Sun, consistent with its detailed
spectral class, which appends the note "cyanogen-weak" and which
reveals a low carbon-nitrogen content. All alone, with no known
companions, the star will quickly -- in astronomical terms -- pass
us and leave the vicinity of the Sun.