An outer shade of Pal: Abundance analysis of the outer halo globular
  cluster Palomar 13
  At a Galactocentric distance of 27 kpc, Pal 13 is an old globular cluster
(GC) in the outer halo. We present a chemical abundance analysis of this remote
system from high-resolution spectra obtained with Keck/HIRES. Owing to the low
signal-to-noise ratio of the data, our analysis is based on a coaddition of the
spectra of 18 member stars. We are able to determine integrated abundance
ratios for 16 species of 14 elements, of $\alpha$-elements (Mg,Si,Ca,Ti),
Fe-peak (Sc,Mn,Cr,Ni,Cu,and Zn), and n-capture elements (Y,Ba). While the mean
Na abundance is found to be slightly enhanced and halo-like, our method does
not allow us to probe an abundance spread that would be expected in this light
element if multiple populations are present in Pal 13. We find a metal-poor
mean metallicity of $-1.91\pm0.05$ (statistical) $\pm$ 0.22 (systematic),
confirming that Pal 13 is a typical metal-poor representative of the outer
halo. While there are some differences between individual $\alpha$-elements,
such as halo-like Mg and Si versus the mildly lower Ca and Ti abundances, the
mean [$\alpha$/Fe] of 0.34$\pm$0.06 is consistent with the marginally lower
$\alpha$ component of the halo field and GC stars. We discuss our results in
the context of other objects in the outer halo and consider which of these
objects were likely accreted. We also discuss the properties of their
progenitors. While chemically, Pal 13 is similar to Gaia-Enceladus and some of
its GCs, this is not supported by its kinematic properties. Moreover, its
chemodynamical similarity with NGC 5466, a progeny of the Sequoia accretion
event, might indicate a common origin in this progenitor. However, the
ambiguities in the full abundance space of this comparison emphasize the
difficulties in unequivocally labeling a single GC as an accreted object, let
alone assigning it to a single progenitor. (Abridged)
