The lowest detected stellar Fe abundance: The halo star SMSS J160540.18-144323.1

Thomas Nordlander, Michael Stanley Bessell, Gary Da Costa, Dougal Mackey, Martin Asplund, Andrew Casey, Anirudh Chiti, Rana Ezzeddine, Anna Frebel, Karin Lind, Anna F Marino, Simon Murphy, John Norris, Brian Schmidt, David Yong

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We report the discovery of SMSS J160540.18-144323.1, a new ultra metal-poor halo star discovered with the SkyMapper telescope. We measure left[rm Fe/rm Hright]= -6.2 pm 0.2 (1D LTE), the lowest ever detected abundance of iron in a star. The star is strongly carbon-enhanced, left[rm C/rm Feright] = 3.9 pm 0.2, while other abundances are compatible with an α-enhanced solar-like pattern with left[rm Ca/rm Feright] = 0.4 pm 0.2, left[rm Mg/rm Feright] = 0.6 pm 0.2, left[rm Ti/rm Feright] = 0.8 pm 0.2, and no significant s- or r-process enrichment, left[rm Sr/rm Feright] lt 0.2 and left[rm Ba/rm Feright] lt 1.0 (3σ limits). Population III stars exploding as fallback supernovae may explain both the strong carbon enhancement and the apparent lack of enhancement of odd-Z and neutron-capture element abundances. Grids of supernova models computed for metal-free progenitor stars yield good matches for stars of about 10, rm M_odot imparting a low kinetic energy on the supernova ejecta, while models for stars more massive than roughly 20, rm M_odot are incompatible with the observed abundance pattern.

Original languageEnglish
Pages (from-to)L109-L113
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
Publication statusPublished - Sep 2019


  • stars: abundances
  • stars: individual: SMSS J160540.18-144323.1
  • stars: Population III

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