BPS CS31082-0001, named Cayrel's Star , is an old Population II star located in a distance of 4 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.
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.
- Beers, T. C., G. W. Preston and S. A. Shectman, A search for stars of very low metal abundance. I., Astron. J., 90, 2089–2102 (1985)
- Beers, T. C., G. W. Preston and S. A. Shectman, A search for stars of very low metal abundance. II., Astron. J., 103, 1987–2034 (1992)
- Cayrel, R., et al. Measurement of stellar age from uranium decay, Nature, Volume 409, Issue 6821, pp. 691–692 (2001)
- Schatz, H., al. Thorium and Uranium Chronometres applied to CS 31082-001, Astrophysical Journal, 579 (2002) 628–638