CHERTAN (Theta Leonis). It's hard to know what to call this star, which lies toward the back end of Leo (the Lion), that is, which one of its three names: the seemingly oldest, "Coxa" (Latin, referring to the "hip" of the Lion), Chertan (from "al-khurtan," Arabic, used for both it and Delta in referring to "ribs"), or another reduction of the same Arabic name, "Chort." Recent scholars seem to prefer Chertan, so let's adopt it here, though any of them might suffice. Given the confusion, it's clearly better to call the star by its Greek letter name of Theta Leonis. At first glance, it's just another one of those naked-eye (third magnitude, 3.34), white, class A (A2) hydrogen-fusing dwarfs made so familiar by Sirius, Vega, Fomalhaut, Altair, and a huge number of others. Yet, like any of them, it has its own individual characteristics. Its somewhat fainter appearance is the result of a goodly distance of 178 light years. From a surface with a temperature heated to 9320 Kelvin (with significant uncertainty), it radiates at a rate equal to that of 120 Suns, which in turn give it a radius of 4.3 times solar. While rotating faster than the Sun (at least 23 km/s at the equator), it is spinning rather slowly for its class, speed and size giving it a rotation period under 9 days. While still a dwarf, it is dangerously close to giving up hydrogen fusion, which makes it a bit difficult to assess accurate mass, which lies between 2.75 and 2.9 solar depending on its exact state of evolution. This near-subgiant began its life roughly 450 million years ago as a hotter class B8 star. Though so far seemingly ordinary, Theta Leo is a good example of a "metallic- line" star, one in which the chemical abundance ratios are distinctly non-solar, such stars then rather difficult to classify accurately. Lighter elements (like calcium and scandium) are under-abundant, while some heavier ones (including even iron) are over-abundant. Iron could range from 20 percent greater than solar to as much as over a factor of two depending on whom you ask. Strontium and barium could respectively range as high as 5 to 8 times "normal." The metallic-line syndrome is explained by the diffusion of atoms in the quiet atmosphere of the more slowly rotating (and thus less-stirred) warm stars, wherein some elements are lofted to the stellar surface by radiation pressure, while others sink down and more or less out of sight. No companion is evident. While some features of the star are not certain, what is assured is that it will die eventually as a relatively massive white dwarf.
Written by Jim Kaler 4/27/07. Return to STARS.