Delta Crateris - Labrum

Delta Crateris is, at magnitude 3.56, the brightest star in Crater, the Cup. The constellation was named by the ancients as a classical drinking vessel, given to Apollo to slake his thirst. Bayer most likely named its stars in positional order, the α and β stars lying directly on the back of Hydra, the Water Serpent.

δ Crt also has the traditional name Labrum, which is a Latin title referring to the Holy Grail from which Jesus and his apostles drank at the Last Supper.

Properties

In reality, δ Crt is an orange class K0 III giant with a surface temperature of 4600 K, lying 195 light years away. Allowing for infrared radiation, it has a luminosity 175 times the Sun's, and an inferred radius 21 times solar. The star has no companion, and appears to be single.

Labrum is a classic 2.5 solar mass "clump giant" star, one of a great number of naked-eye stars with all about the same temperature and luminosity, that quietly fuse their core helium into carbon and oxygen. The next step in its evolution is to become an even larger giant, then a Mira-type variable, and ultimately a white dwarf.

δ Crt's most outstanding characteristic is its rather low metal content, which is consistently measured by a variety of observers to be around 40% of the Sun's. The star has a rather high velocity of 68 km/sec relative to the Sun, well over twice the average among local stars. The high speed indicates that the star has come from outside the thin disk of the Galaxy, from the older galactic halo where the raw material that made up the star was not quite so enriched in heavy elements by supernovae.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]