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DELTA CRT (Delta Crateris). For reasons known only to the name-giverJohannes Bayer, the Alpha star (Alkes) ofCrater (the Cup) is distinctly second inrank after his Delta and almost as faint as Gamma. Most likelyBayer named them in positional order, the Alpha and Beta starslying directly on the back ofHydra, theWater Serpent. If Delta Crateris, which carries no popular name,were not Crater's luminary, it would receive little attention atall. As does Crater itself, as its brightest star is merely fourthmagnitude (though at 3.56, just over the line). It is surprisingthat the constellation was named by the ancients at all, except forthe fact that it rather does resemble a classical drinking vessel,and was given to Apollo to slake his thirst. In reality, Delta Crtis an orange class K (K0, once thought to be closer to G8) giant(oddly, the same as Alkes) 195 light years away with a surfacetemperature of 4600 Kelvin. Allowance for a fair bit of infraredradiation gives the star a luminosity 175 times that of theSun, from which we infer a radius 21 timessolar. Lonely in its dim constellation, the star has no companion,but appears to be quite single. It is a classic 2.5 solar mass (orso) "clump" star, part of a great gang of naked-eye stars all ofabout the same character that quietly fuse their core helium intocarbon and oxygen, the next step to become an even larger giant andultimately aMira variable and then a whitedwarf. Delta Crt's most outstanding characteristic is its ratherlow metal content, which is consistently measured by a variety ofobservers to be around 40 percent that of the Sun, the opposite ofAlkes, which may be metal-rich. Consistently, the star has arather high velocity of 68 kilometers per second relative to theSun (almost all of it across the line of sight), well over twicethat common among local stars. The high speed shows that the starhas come from outside the thin disk of the Galaxy that holds theSun, from an older part of the Galaxy where the raw material thatmade the star was not quite so enriched in heavy elements byexploding stars.
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