Chemical abundances of distant extremely metal-poor unevolved stars P. Bonifacio, L. Sbordone, E. Caffau, H.-G. Ludwig, M. Spite, J. I. González Hernández and N. T. Behara A&A, 542 (2012) A87 Published online: 12 June 2012 DOI: 10.1051/0004-6361/201219004