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.
Written by Jim Kaler. Return to STARS.