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Published online by Cambridge University Press: 19 July 2016
We have observed 23 halo stars with space velocities and metallicities [Fe/H] ≤ −0.6. Twelve of these 23 show the more extreme properties and [Fe/H] ≤ −1.4 and should therefore constitute an especially old, homogeneous subgroup. The principal results for these 12 extreme halo stars and 5 similar stars observed in previous studies are that (1) a single, well defined relation, previously discovered and discussed by Spite and Spite, exists without exception between the atmospheric Li/H ratio and Te, and (2) at Te ≥ 5600 K the average lithium abundance is <Li/H> = 1.2 ± 0.3 × 10−10. The latter value constitutes a lower limit on the 7Li fraction produced in primordial nucleosynthesis and thereby significantly constrains the cosmic ratio of baryons to photons.