The chemical composition of a regular halo globular cluster: NGC 5897
  We report for the first time on the chemical composition of the halo cluster
NGC 5897 (R=12.5 kpc), based on chemical abundance ratios for 27 alpha-,
iron-peak, and neutron-capture elements in seven red giants. From our
high-resolution, high signal-to-noise spectra obtained with the Magellan/MIKE
spectrograph, we find a mean iron abundance from the neutral species of [Fe/H]
= -2.04 +/- 0.01 (stat.) +/- 0.15 (sys.), which is more metal-poor than implied
by previous photometric and low-resolution spectroscopic studies. NGC 5897 is
alpha-enhanced (to 0.34 +/- 0.01 dex) and shows Fe-peak element ratios typical
of other (metal-poor) halo globular clusters (GCs) with no overall, significant
abundance spreads in iron nor in any other heavy element. Like other GCs, NGC
5897 shows a clear Na-O anti-correlation, where we find a prominent primordial
population of stars with enhanced O abundances and ~Solar Na/Fe ratios, while
two stars are Na-rich, providing chemical proof of the presence of multiple
populations in this cluster. Comparison of the heavy element abundances with
the Solar-scaled values and the metal poor GC M15 from the literature confirms
that NGC 5897 has experienced only little contribution from s-process
nucleosynthesis. One star of the first generation stands out in that it shows
very low La and Eu abundances. Overall, NGC 5897 is a well-behaved GC showing
archetypical correlations and element-patterns, with little room for surprises
in our data. We suggest that its lower metallicity could explain the unusually
long periods of RR Lyr that were found in NGC 5897.
