CHI CAR (Chi Carinae). Third magnitude (but not by much, 3.47) Chi Carinae, which lies immediately to the east of Canopus (the sky's second brightest star) and just to the southwest of magnificent Gamma Velorum (meaning you have to be south of 38 degrees south latitude to see it), is just too obscure within its fine setting to carry any sort of proper name. But its history lends itself to making one up: "Stella Rejecta," the rejected star, not once, not twice, not thrice (a word you don't get to use very often), but four times. This nicely-blue class B (B3) subgiant shines at us from a decently large distance of 387 light years through relatively clear space, as it is dimmed by only about a tenth of a magnitude by interstellar dust. The temperature of 18,000 Kelvin, appropriate for a B3 star, is, however, still not well-defined, other values up to 800 Kelvin hotter and cooler. After allowing for a lot of ultraviolet light, we then find that Chi Car shines 2375 times more brightly than does the Sun, leading to a radius of 5 times solar and a mass of 6.7 times that of the Sun. An ill-determined equatorial rotation speed of 78 kilometers per second gives a short rotation period of under 3.2 days (as opposed to the 25-day rotation period of the Sun). So where did our new name for it come from? Why might Chi Car feel (if it could feel) so rejected? To begin, it is classed as a subgiant, one that has given up core hydrogen fusion and is preparing to become a real giant star. Luminosity, temperature, and theory, though, toss it out of the subgiant realm and instead show it to be a hydrogen-fusing dwarf, though one entering the late stages of dwarfhood (which will end when the star hits an age of 45 million years). That's not so bad, as many stars are actually not quite what they are classed as based on their spectra alone. It's the next three that make the name. First, Chi is classed as B3p, the "p" for "peculiar," as it was thought to be silicon-rich (as a result of elemental diffusion), even helium-poor. Nope. Detailed abundance analysis shows the chemistry to be quite normal. Second, Chi was for a long time thought to be a Beta Cephei variable (one that varies minutely over multiple short periods), Chi by 0.015 magnitudes in 2.4 hours. No again, not a variable at all. Finally, the star is listed as belonging to the vast Scorpius-Centaurus association of hot class O and B stars (and which has numerous subdivisions of stars born more or less at the same time). But it doesn't. Instead, without even a binary companion to keep it company, it's all alone. (Thanks to Latin scholar David Bright.)
Written by Jim Kaler 4/11/08. Return to STARS.