Sc and neutron-capture abundances in Galactic low- and high-alpha field
  halo stars
  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-alpha halo and thick-disc stars) based on the
[alpha/Fe] abundance ratio and their kinematics as discovered by Nissen &
Schuster. We find differences between the low- and high-alpha 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-alpha stars have a lower abundance compared to the high-alpha stars. The
low-alpha 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-alpha 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-alpha
population. By comparing the low-alpha population with AGB stellar models, we
place constraints on the mass range of the AGB stars.
