Cayrel's Star

BPS CS31082-0001, named Cayrel's Star /keɪˈrɛlz/,^[4] is an old Population II star located in a distance of 2.1 kpc^[2] 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 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.

BPS CS31082-0001

Observation data Epoch J2000      Equinox J2000
Constellation	Cetus[1]
Right ascension	01h 29m 31.1311s[2]
Declination	−16° 00′ 45.496″[2]
Apparent magnitude (V)	11.642[3]
Astrometry
Proper motion (μ)	RA: 11.745[2] mas/yr Dec.: −42.709[2] mas/yr
Parallax (π)	0.4806±0.0462 mas[2]
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 (eg. CS22892-052, BD+17°3248, HE 1523-0901) CS31082-001 has higher abundances of the actinides (Th, U), but a surprisingly low Pb abundance.

See also

• HE 0107-5240
• HE 1327-2326
• SDSS J102915+172927
• SMSS J031300.36-670839.3