The chemically most primitive stars provide constraints on the nature of the first stellar objects that formed in the Universe; elements other than hydrogen, helium and traces of lithium present within these objects were generated by nucleosynthesis in the very first stars. The relative abundances of elements in the surviving primitive stars reflect the masses of the first stars, because the pathways of nucleosynthesis are quite sensitive to stellar masses. Several models1,2,3,4,5 have been suggested to explain the origin of the abundance pattern of the giant star HE0107–5240, which hitherto exhibited the highest deficiency of heavy elements known1,6. Here we report the discovery of HE1327–2326, a subgiant or main-sequence star with an iron abundance about a factor of two lower than that of HE0107–5240. Both stars show extreme overabundances of carbon and nitrogen with respect to iron, suggesting a similar origin of the abundance patterns. The unexpectedly low Li and high Sr abundances of HE1327–2326, however, challenge existing theoretical understanding: no model predicts the high Sr abundance or provides a Li depletion mechanism consistent with data available for the most metal-poor stars.
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We thank A. Steinhauer and C. Thom for obtaining additional observations, N. Iwamoto, K. Maeda, T. Suda, N. Tominaga and H. Umeda for valuable discussions and L. Wisotzki and D. Reimers for leading the HES. This work was supported by the Astronomical Society of Australia (A.F.), Australian Research Council (M.A., A.F., J.E.N.), Ministry of Education, Culture, Sports, Science and Technology in Japan and JSPS (all Japanese co-authors), Deutsche Forschungsgemeinschaft (N.C.), Swedish Research Council (P.S.B., K.E.), US National Science Foundation (T.C.B.) and JINA (T.C.B., N.C., A.F., J.E.N.). This work is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.
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