BPS CS31082-0001, named Cayrel's Star /keɪˈrɛlz/,[3] is an old Population II star located in a distance of 2.1 kpc[1] 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 | |
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Constellation | Cetus |
Right ascension | 01h 29m 31.1311s[1] |
Declination | −16° 00′ 45.496″[1] |
Apparent magnitude (V) | 11.642[2] |
Astrometry | |
Proper motion (μ) | RA: 11.745[1] mas/yr Dec.: −42.709[1] mas/yr |
Parallax (π) | 0.4806 ± 0.0462 mas[1] |
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.