Cayrel's Star

BPS CS31082 -001 ( Cayrels star) is an old Population II stars in the halo of the Milky Way. It belongs to the rare class of ultra metal-poor stars ( metallicity [Fe / H] = -2.9 ), and in turn to the rare subclass with an overabundance of r-process elements. He was discovered by Tim C. Beers and employees with the Curtis Schmidt telescope at Cerro Tololo Inter- American Observatory in Chile. Used Roger Cayrel and staff the Very Large Telescope ( VLT ) of the European Southern Observatory in Paranal, for high-resolution optical spectroscopy to determine elemental abundances to Chile.

The ratio of thorium to uranium 232 238 made ​​it possible to determine the age. This star is about 12.5 billion years old, one of the oldest ever.

Compared to other ultra- metal-poor, r-process - enriched stars ( as CS22892 -052, BD 17 ° 3248 ) has CS31082 -001 higher abundances of actinides (Th, U), but a surprisingly low content of lead ( Pb).