Sneden's Star
BPS CS22892-0052 is an old population II star located at a distance of 4.7 kpc in the galactic halo. It belongs to a class of ultra-metal-poor stars, specifically the very rare subclass of neutron-capture enhanced stars. It was discovered by Tim C. Beers and collaborators with the Curtis Schmidt telescope at the Cerro Tololo Inter-American Observatory in Chile. Extended high-resolution spectroscopic observations since around 1995 allowed observers to determine the abundances of 53 chemical elements in this star, as of December 2005 only second in number to the Sun.
From barium on, all elements show the pattern of the r-process contribution to the abundances of the elements in the Solar System.
Comparing the observed abundances for a stable element such as europium and the radioactive element thorium to calculated abundances of an r-process in a type II supernova explosion have allowed observers to determine the age of this star to be about 13 billion years. Similar ages have been derived for other ultra-metal-poor stars from thorium-to-uranium ratios.
