@article{d5917365ebe946c3a3eaef5843e336bd,
title = "A primordial star in the heart of the Lion",
abstract = "Context. The discovery and chemical analysis of extremely metal-poor stars permit a better understanding of the star formation of the first generation of stars and of the Universe emerging from the Big Bang. Aims. We report the study of a primordial star situated in the centre of the constellation Leo (SDSS J102915+172927). Methods. The star, selected from the low-resolution spectrum of the Sloan Digital Sky Survey, was observed at intermediate (with X-Shooter at VLT) and at high spectral resolution (with UVES at VLT). The stellar parameters were derived from the photometry. The standard spectroscopic analysis based on 1D ATLAS models was completed by applying 3D and non-LTE corrections. Results.An iron abundance of [Fe/H] =-4.89 makes SDSS J102915+172927 one of the lowest [Fe/H] stars known. However, the absence of measurable C and N enhancements indicates that it has the lowest metallicity, Z ≤ 7.40 × 10 -7 (metal-mass fraction), ever detected. No oxygen measurement was possible. Conclusions. The discovery of SDSS J102915+172927 highlights that low-mass star formation occurred at metallicities lower than previously assumed. Even lower metallicity stars may yet be discovered, with a chemical composition closer to the composition of the primordial gas and of the first supernovae.",
keywords = "Cosmology: observations, Galaxy: evolution, Stars: Population II, Stars: Population III, Stars: abundances, Stars: formation",
author = "E. Caffau and P. Bonifacio and P. Fran{\c c}ois and M. Spite and F. Spite and S. Zaggia and Ludwig, {H. G.} and M. Steffen and L. Mashonkina and L. Monaco and L. Sbordone and P. Molaro and R. Cayrel and B. Plez and V. Hill and F. Hammer and S. Randich",
note = "Funding Information: The authors would like to thank A. Chieffi and M. Limongi, who kindly provided a set of unpublished isochrones. The authors thank M. Barbieri for providing the Galactic model for the orbit calculations and for many useful discussions. We are grateful to R. Scholz for useful discussions on the proper motion measurements. We also thank P. Ochner for the observations at the Asiago telescope. E. Caffau and P. Bonifacio wish to thank ESO for the hospitality at ESO-Santiago provided during the preparation of the paper. P. Bonifacio, P. Fran{\c c}ois, M. Spite, F. Spite, R. Cayrel, B. Plez and V. Hill acknowledge support from the Programme National de Physique Stellaire (PNPS) and the Programme National de Cosmologie et Galaxies (PNCG) of the Institut National de Sciences de l{\textquoteright}Universe of CNRS. This paper is also based on observations collected at the Asiago Observatory (Italy). L. Mashonkina is supported by the Presidium RAS Programme “Origin, structure, and evolution of cosmic objects” (No. P-19) and the Swiss National Science Foundation (SCOPES project No. IZ73Z0-128180/1). H.G.L. acknowledges financial support by the Sonderforschungsbereich SFB 881 “The Milky Way System” (subproject A4) of the German Research Foundation (DFG). The authors would like to thank the anonymous referee for the useful suggestions.",
year = "2012",
doi = "10.1051/0004-6361/201118744",
language = "English",
volume = "542",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}