DELTA CRT (Delta Crateris). For reasons known only to the name-giver Johannes Bayer, the Alpha star (Alkes) of Crater (the Cup) is distinctly second in rank after his Delta and almost as faint as Gamma. Most likely Bayer named them in positional order, the Alpha and Beta stars lying directly on the back of Hydra, the Water Serpent. If Delta Crateris, which carries no popular name, were not Crater's luminary, it would receive little attention at all. As does Crater itself, as its brightest star is merely fourth magnitude (though at 3.56, just over the line). It is surprising that the constellation was named by the ancients at all, except for the fact that it rather does resemble a classical drinking vessel, and was given to Apollo to slake his thirst. In reality, Delta Crt is an orange class K (K0, once thought to be closer to G8) giant (oddly, the same as Alkes) 195 light years away with a surface temperature of 4600 Kelvin. Allowance for a fair bit of infrared radiation gives the star a luminosity 175 times that of the Sun, from which we infer a radius 21 times solar. Lonely in its dim constellation, the star has no companion, but appears to be quite single. It is a classic 2.5 solar mass (or so) "clump" star, part of a great gang of naked-eye stars all of about the same character that quietly fuse their core helium into carbon and oxygen, the next step to become an even larger giant and ultimately a Mira variable and then a white dwarf. Delta Crt's most outstanding characteristic is its rather low metal content, which is consistently measured by a variety of observers to be around 40 percent that of the Sun, the opposite of Alkes, which may be metal-rich. Consistently, the star has a rather high velocity of 68 kilometers per second relative to the Sun (almost all of it across the line of sight), well over twice that common among local stars. The high speed shows that the star has come from outside the thin disk of the Galaxy that holds the Sun, from an older part of the Galaxy where the raw material that made the star was not quite so enriched in heavy elements by exploding stars.
Written by Jim Kaler. Return to STARS.