Vol. 542
In section 5. Galactic structure, stellar clusters and populations

A primordial star in the heart of the Lion

by E. Caffau, P. Bonifacio, P. Francois, M. Spite, F. Spite, S. Zaggia, H.-G. Ludwig, M. Steffen, L. Mashonkina, L. Monaco, L. Sbordone, P. Molaro, R. Cayrel, B. Plez, V. Hill, F. Hammer, and S. Randich, A&A 542, A51

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The most metal-poor star discovered to date is fully chemically analyzed based on high-resolution spectroscopy. The star is SDSS J102915+172927 and was selected from the Sloan Digital Sky Survey low-resolution spectroscopic survey. Follow-up higher-resolution observations were made with the X-shooter and UVES spectrographs at the VLT. The measured iron abundance, [Fe/H]=-4.89, makes this one of the most iron-poor stars known. The absence of measurable carbon and nitrogen features in the spectra shows that this star has the lowest total metallicity yet detected, Z<= 7.4 x 10^-7. The discovery of this star establishes that low-mass star formation has occurred at metallicities lower than previously assumed. This has implications for our understanding of the first generation of stars in the early Universe, and their impact on subsequent generations of stars.