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

C. K. Fishlock, D. Yong, A. I. Karakas, A. Alves-Brito, J. Melendez, P. E. Nissen, C. Kobayashi, A. R. Casey

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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
Pages (from-to)4672–4682
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date11 Jan 2017
Publication statusPublished - 1 May 2017


  • astro-ph.SR
  • astro-ph.GA


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