  Previous work on the abundances of C, O, Na, Mg, Si, Ca, Ti, Cr, Mn, Fe, Ni,
Cu, and Zn in low-alpha (accreted) and high-alpha (in situ born) halo stars is
extended to include the abundances of Sc, V, and Co, enabling us to study the
nucleosynthesis of all iron-peak elements along with the lighter elements. The
Sc, V, and Co abundances were determined from a 1D MARCS model-atmosphere
analysis of equivalent widths of atomic lines in high signal-to-noise, high
resolution spectra assuming local thermodynamic equilibrium (LTE). In addition,
new 3D and/or non-LTE calculations were used to correct the 1D LTE abundances
for several elements including consistent 3D non-LTE calculations for Mg. The
two populations of accreted and in situ born stars are well separated in
diagrams showing [Sc/Fe], [V/Fe], and [Co/Fe] as a function of [Fe/H]. The
[X/Mg] versus [Mg/H] trends for high-alpha and low-alpha stars were used to
determine the yields of core-collapse and Type Ia supernovae. The largest Type
Ia contribution occurs for Cr, Mn, and Fe, whereas Cu is a pure core-collapse
element. Sc, Ti, V, Co, Ni, and Zn represent intermediate cases. A comparison
with yields calculated for supernova models shows poor agreement for the
core-collapse yields. The Ia yields suggest that sub-Chandrasekhar-mass Type Ia
supernovae provide a dominant contribution to the chemical evolution of the
host galaxies of the low-alpha stars. A substructure in the abundances and
kinematics of the low-alpha stars suggests that they arise from at least two
different satellite accretion events, Gaia-Sausage-Enceladus and Thamnos.

Astrophysics of Galaxies;Solar and Stellar Astrophysics