Cayrel's Star
BPS CS31082-0001, named Cayrel's Star /keɪˈrɛlz/, is an old Population II star located in a distance of 2.1 kpc in the galactic halo. It belongs to the class of ultra-metal-poor stars (metallicity [Fe/H] = -2.9), 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 and analyzed by Roger Cayrel and collaborators. They used the Very Large Telescope (VLT) at the European Southern Observatory in Paranal, Chile for high-resolution optical spectroscopy to determine elemental abundances. The thorium-232 to uranium-238 ratio was used to determine the age. It is estimated to be about 12.5 billion years old, making it one of the oldest known.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cetus |
| Right ascension | 01h 29m 31.1311s |
| Declination | −16° 00′ 45.496″ |
| Apparent magnitude (V) | 11.642 |
| Astrometry | |
| Proper motion (μ) | RA: 11.745 mas/yr Dec.: −42.709 mas/yr |
| Parallax (π) | 0.4806 ± 0.0462 mas |
| Distance | 6,800 ± 700 ly (2,100 ± 200 pc) |
| Other designations | |
BD−16° 251, CS31082-001, Cayrel's Star | |
| Database references | |
| SIMBAD | data |
Compared to other ultra-metal-poor, r-process enriched stars (as CS22892-052, BD +17° 3248, HE 1523-0901) CS31082-001 has higher abundances of the actinides (Th, U), but a surprisingly low Pb abundance.