An Intermediate-age Alpha-rich Galactic Population in K2
  We explore the relationships between the chemistry, ages, and locations of
stars in the Galaxy using asteroseismic data from the K2 mission and
spectroscopic data from the Apache Point Galactic Evolution Experiment survey.
Previous studies have used giant stars in the Kepler field to map the
relationship between the chemical composition and the ages of stars at the
solar circle. Consistent with prior work, we find that stars with high
[Alpha/Fe] have distinct, older ages in comparison to stars with low
[Alpha/Fe]. We provide age estimates for red giant branch (RGB) stars in the
Kepler field, which support and build upon previous age estimates by taking
into account the effect of alpha-enrichment on opacity. Including this effect
for [Alpha/Fe]-rich stars results in up to 10% older ages for low-mass stars
relative to corrected solar mixture calculations. This is a significant effect
that Galactic archaeology studies should take into account. Looking beyond the
Kepler field, we estimate ages for 735 red giant branch stars from the K2
mission, mapping age trends as a function of the line of sight. We find that
the age distributions for low- and high-[Alpha/Fe] stars converge with
increasing distance from the Galactic plane, in agreement with suggestions from
earlier work. We find that K2 stars with high [Alpha/Fe] appear to be younger
than their counterparts in the Kepler field, overlapping more significantly
with a similarly aged low-[Alpha/Fe] population. This observation may suggest
that star formation or radial migration proceeds unevenly in the Galaxy.
