Cayrel's Star

BPS CS31082-0001
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

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.

Quick Facts Observation data Epoch J2000 Equinox J2000, Constellation ...

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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.

[1]
Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
[2]
Munari, U.; Henden, A.; Frigo, A.; Zwitter, T.; Bienaymé, O.; Bland-Hawthorn, J.; Boeche, C.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Grebel, E. K.; Helmi, A.; Kordopatis, G.; Levine, S. E.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G. M.; Siebert, A.; Siviero, A.; Smith, T. C.; Steinmetz, M.; Templeton, M.; Terrell, D.; Welch, D. L.; Williams, M.; Wyse, R. F. G. (2014). "APASS Landolt-Sloan BVgri Photometry of RAVE Stars. I. Data, Effective Temperatures, and Reddenings". The Astronomical Journal. 148 (5): 81. arXiv:1408.5476. Bibcode:2014AJ....148...81M. doi:10.1088/0004-6256/148/5/81. hdl:1885/19979. S2CID 56127278.
[3]
Space Math @ NASA

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

See also