1. Research School of Astronomy & Astrophysics, The Australian National University, Cotter Road, Weston Creek, Australian Capital Territory 2611, Australia
2. National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
3. Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
4. Department of Physics and Space Sciences, Uppsala Astronomical Observatory, Box 515, SE-751 20 Uppsala, Sweden
5. Department of Physics and Astronomy, and Joint Institute for Nuclear Astrophysics (JINA), Michigan State University, East Lansing, Michigan 48824, USA
6. Department of Physics, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
7. Institute of Astronomy, School of Science, University of Tokyo, Mitaka, Tokyo 181-0015, Japan
8. Department of Astronomy, School of Science, University of Tokyo, Tokyo 113-0033, Japan
9. Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
10. Liberal Arts Education Center, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan

Correspondence to: Anna Frebel¹ Correspondence and requests for materials should be addressed to A.F. (Email: anna@mso.anu.edu.au).

Abstract

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 models^{1, 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 known^{1, 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.

1. Research School of Astronomy & Astrophysics, The Australian National University, Cotter Road, Weston Creek, Australian Capital Territory 2611, Australia
2. National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
3. Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
4. Department of Physics and Space Sciences, Uppsala Astronomical Observatory, Box 515, SE-751 20 Uppsala, Sweden
5. Department of Physics and Astronomy, and Joint Institute for Nuclear Astrophysics (JINA), Michigan State University, East Lansing, Michigan 48824, USA
6. Department of Physics, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
7. Institute of Astronomy, School of Science, University of Tokyo, Mitaka, Tokyo 181-0015, Japan
8. Department of Astronomy, School of Science, University of Tokyo, Tokyo 113-0033, Japan
9. Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
10. Liberal Arts Education Center, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan

Correspondence to: Anna Frebel¹ Correspondence and requests for materials should be addressed to A.F. (Email: anna@mso.anu.edu.au).

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