Detailed chemical abundance analysis of the thick disk star cluster Gaia
  1
  Star clusters, particularly those objects in the disk-bulge-halo interface
are as of yet poorly charted, albeit carrying important information about the
formation and the structure of the Milky Way. Here, we present a detailed
chemical abundance study of the recently discovered object Gaia 1. Photometry
has previously suggested it as an intermediate-age, moderately metal-rich
system, although the exact values for its age and metallicity remained
ambiguous in the literature. We measured detailed chemical abundances of 14
elements in four red giant members, from high-resolution (R=25000) spectra that
firmly establish Gaia 1 as an object associated with the thick disk. The
resulting mean Fe abundance is $-0.62\pm$0.03(stat.)$\pm$0.10(sys.) dex, which
is more metal-poor than indicated by previous spectroscopy from the literature,
but it is fully in line with values from isochrone fitting. We find that Gaia 1
is moderately enhanced in the $\alpha$-elements, which allowed us to
consolidate its membership with the thick disk via chemical tagging. The
cluster's Fe-peak and neutron-capture elements are similar to those found
across the metal-rich disks, where the latter indicate some level of
$s$-process activity. No significant spread in iron nor in other heavy elements
was detected, whereas we find evidence of light-element variations in Na, Mg,
and Al. Nonetheless, the traditional Na-O and Mg-Al (anti-)correlations,
typically seen in old globular clusters, are not seen in our data. This
confirms that Gaia 1 is rather a massive and luminous open cluster than a
low-mass globular cluster. Finally, orbital computations of the target stars
bolster our chemical findings of Gaia 1's present-day membership with the thick
disk, even though it remains unclear, which mechanisms put it in that place.
