High resolution spectroscopic follow-up of the most metal-poor candidates from SkyMapper DR1.1

D. Yong, G. S. Da Costa, M. S. Bessell, A. Chiti, A. Frebel, X. Gao, K. Lind, A. D. Mackey, A. F. Marino, S. J. Murphy, T. Nordlander, M. Asplund, A. R. Casey, C. Kobayashi, J. E. Norris, B. P. Schmidt

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We present chemical abundances for 21 elements (from Li to Eu) in 150 metal-poor Galactic stars spanning -4.1 < [Fe/H] < -2.1. The targets were selected from the SkyMapper survey and include 90 objects with [Fe/H] ≤ -3 of which some 15 have [Fe/H] ≤ -3.5. When combining the sample with our previous studies, we find that the metallicity distribution function has a power-law slope of Δ(log N)/Δ[Fe/H] = 1.51 ± 0.01 dex per dex over the range -4 ≤ [Fe/H] ≤ -3. With only seven carbon-enhanced metal-poor stars in the sample, we again find that the selection of metal-poor stars based on SkyMapper filters is biased against highly carbon-rich stars for [Fe/H] > -3.5. Of the 20 objects for which we could measure nitrogen, 11 are nitrogen-enhanced metal-poor (NEMP) stars. Within our sample, the high NEMP fraction (55 per cent ± 21 per cent) is compatible with the upper range of predicted values (between 12 per cent and 35 per cent). The chemical abundance ratios [X/Fe] versus [Fe/H] exhibit similar trends to previous studies of metal-poor stars and Galactic chemical evolution models. We report the discovery of nine new r-I stars, four new r-II stars, one of which is the most metal-poor known, nine low-α stars with [α/Fe] ≤ 0.15 as well as one unusual star with [Zn/Fe] = +1.4 and [Sr/Fe] = +1.2 but with normal [Ba/Fe]. Finally, we combine our sample with literature data to provide the most extensive view of the early chemical enrichment of the Milky Way Galaxy.

Original languageEnglish
Pages (from-to)4102-4119
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date15 Jul 2021
Publication statusPublished - 1 Nov 2021


  • astro-ph.GA
  • astro-ph.SR
  • early universe
  • stars: Population II
  • Galaxy: abundances
  • stars: abundances


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