ANKAA (Alpha Phoenicis). Well into the southern hemisphere lies
the modern constellation Phoenix, the
mythical Phoenix or Firebird, named by southern hemisphere
explorers and first noted in Bayer's Uranometria. The name of the
bright second magnitude (2.39) luminary derives from a late
application of the Arabic for the marvelous bird. Phoenix has a
longer history, however, as the stars in the area were considered
by the Arabs to be a "boat," giving Ankaa a second name, "Nair al
Zaurak," the "bright one of the boat," a portion of the name ("Zaurak") now applied to Gamma Eridani.
Ankaa, a class K (K0) giant, is among the common kinds of stars
that make so much of the constellation patterns. At a distance of
77 light years, it radiates 86 solar luminosities with a soft
yellow-orange light from a surface estimated to have a temperature
of about 4800 Kelvin (no accurate determinations are readily
available). With a mass of around 2.5 times that of the Sun and a radius 13 times solar, the star seems
to be in its short-term but stable core-helium fusing stage, from
which it will eventually become a brighter and larger red giant, at
which point it will expel its outer shell and become a tiny white
dwarf, the fate of all such "K giants." In spite of its large
size, Ankaa has a rotation speed similar to (and maybe even greater
than) that of the Sun (about 2 kilometers per second at the
equator), a legacy of the star's origin as a hot class A or even a
class B star (these classes fast spinners). Even so, Ankaa might
take up to a year to make a full rotation, the spin responsible for
some activity that makes the star a modest X-ray source. Ankaa's
space velocity, however, is high, 88 kilometers per second relative
to the Sun. The
star's future behavior will be witnessed by a low-mass companion
about which nothing is known, one of the few that is detected in
two ways, by the spectrograph through the orbital velocity it
imposes on the bright star, and directly. Orbiting eccentrically
at an average distance of some 7 astronomical units (35 percent
farther than Jupiter is from the Sun), the companion takes 10.5
years to make a full circuit.