The K2 Galactic Archaeology Program Data Release 3: Age-abundance
  patterns in C1-C8 and C10-C18
  We present the third and final data release of the K2 Galactic Archaeology
Program (K2 GAP) for Campaigns C1-C8 and C10-C18. We provide asteroseismic
radius and mass coefficients, $\kappa_R$ and $\kappa_M$, for $\sim 19,000$ red
giant stars, which translate directly to radius and mass given a temperature.
As such, K2 GAP DR3 represents the largest asteroseismic sample in the
literature to date. K2 GAP DR3 stellar parameters are calibrated to be on an
absolute parallactic scale based on Gaia DR2, with red giant branch and red
clump evolutionary state classifications provided via a machine-learning
approach. Combining these stellar parameters with GALAH DR3 spectroscopy, we
determine asteroseismic ages with precisions of $\sim 20-30\%$ and compare
age-abundance relations to Galactic chemical evolution models among both low-
and high-$\alpha$ populations for $\alpha$, light, iron-peak, and
neutron-capture elements. We confirm recent indications in the literature of
both increased Ba production at late Galactic times, as well as significant
contribution to r-process enrichment from prompt sources associated with, e.g.,
core-collapse supernovae. With an eye toward other Galactic archaeology
applications, we characterize K2 GAP DR3 uncertainties and completeness using
injection tests, suggesting K2 GAP DR3 is largely unbiased in mass/age and with
uncertainties of $2.9\%\,(\rm{stat.})\,\pm0.1\%\,(\rm{syst.})$ &
$6.7\%\,(\rm{stat.})\,\pm0.3\%\,(\rm{syst.})$ in $\kappa_R$ & $\kappa_M$ for
red giant branch stars and $4.7\%\,(\rm{stat.})\,\pm0.3\%\,(\rm{syst.})$ &
$11\%\,(\rm{stat.})\,\pm0.9\%\,(\rm{syst.})$ for red clump stars. We also
identify percent-level asteroseismic systematics, which are likely related to
the time baseline of the underlying data, and which therefore should be
considered in TESS asteroseismic analysis.
