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.