Sc and neutron-capture abundances in Galactic low- and high-α field halo stars

Publication: Research - peer-reviewJournal article

  • Cherie K. Fishlock
    Cherie K. FishlockResearch School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
  • D. Yong
    D. YongResearch School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
  • Amanda I. Karakas
    Amanda I. KarakasMonash Centre for Astrophysics, School of Physics and Astronomy, Monash University, VIC 3800, Australia
  • Alan Alves Brito
    Alan Alves BritoInstituto de Fisica, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, Porto Alegre, RS, Brazil
  • J. Meléndez
    J. MeléndezDepartamento de Astronomia do IAG/USP, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, SP, Brazil
  • P. E. Nissen
  • C. Kobayashi
    C. KobayashiCentre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire AL10 9AB, UK
  • A. R. Casey
    A. R. CaseyInstitute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
We determine relative abundance ratios for the neutron-capture elements Zr, La, Ce, Nd and Eu for a sample of 27 Galactic dwarf stars with -1.5 <[Fe/H] <-0.8. We also measure the iron-peak element Sc. These stars separate into three populations (low- and high-α halo and thick-disc stars) based on the [α/Fe] abundance ratio and their kinematics as discovered by Nissen & Schuster. We find differences between the low- and high-α groups in the abundance ratios of [Sc/Fe], [Zr/Fe], [La/Zr], [Y/Eu] and [Ba/Eu] when including Y and Ba from Nissen & Schuster. For all ratios except [La/Zr], the low-α stars have a lower abundance compared to the high-α stars. The low-α stars display the same abundance patterns of high [Ba/Y] and low [Y/Eu] as observed in present-day dwarf spheroidal galaxies, although with smaller abundance differences, when compared to the high-α stars. These distinct chemical patterns have been attributed to differences in the star formation rate between the two populations and the contribution of low-metallicity, low-mass asymptotic giant branch (AGB) stars to the low-α population. By comparing the low-α population with AGB stellar models, we place constraints on the mass range of the AGB stars.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Pages (from-to)4672-4682
StatePublished - 1 Apr 2017
Externally publishedYes


  • stars: abundances, Galaxy: halo

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