ALPHA CHA (Alpha Chamaeleontis). Even the brightest star of Chamaeleon (the Chameleon) is but mid-fourth
magnitude (4.07), not much to say for a "luminary" and the Alpha
star. It has no weird properties that make it stand out, and is
single, providing us with no pretty double to admire. It is,
however, an interesting representative of a rare class, a white
class F (F5) giant, which are relatively few and far between. It
might also be fooling us. Fairly close, at an accurately-known
distance of only 63.5 light years (good to half a light year), it
radiates 7.1 solar luminosities from an uncertain 6770 Kelvin
surface, which together yield a radius 2.3 times that of the Sun. Rotating with a minimum equatorial
velocity of 29 kilometers per second, the star makes a full turn in
less than 2.3 days. (Only limits are known, since the axial tilt
is undetermined.) Now the anomalies begin. The theory of stellar
structure shows the star to be not a true giant, but an advanced
hydrogen fusing dwarf of mass 1.55 solar. At an age of about 1.5
billion years, it is however admittedly nearing the end of its
dwarf-life. It even has an outer corona heated through magnetic
action (caused by rotation and convection, as in the Sun) to 3.7
million Kelvin that radiates rather strong X-rays, as might befit
such a star. As stars age, they can change the chemical
compositions of their surfaces. True giants dredge up newly formed
nitrogen (from internal energy-generating nuclear reactions),
leading to a high ratio of nitrogen to carbon. Lithium, on the
other hand, becomes depleted, since it is cycled downward by
convection to hot stellar regions where it is easily destroyed by
other nuclear reactions. Such stars should have both low lithium
and high nitrogen. However, in Alpha Cha, the abundances of both
are curiously high, for reasons not understood, the star thereby
looking old and young at the same time. Consistently, its spectrum
shows it to be a older giant with a dead helium core, yet its
luminosity and temperature show it to be a younger dwarf.