Detailed Chemical Abundances in NGC 5824: Another Metal-Poor Globular
  Cluster with Internal Heavy Element Abundance Variations
  We present radial velocities, stellar parameters, and detailed abundances of
39 elements derived from high-resolution spectroscopic observations of red
giant stars in the luminous, metal-poor globular cluster NGC 5824. We observe
26 stars in NGC 5824 using the Michigan/Magellan Fiber System (M2FS) and two
stars using the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. We derive
a mean metallicity of [Fe/H]=-1.94+/-0.02 (statistical) +/-0.10 (systematic).
The metallicity dispersion of this sample of stars, 0.08 dex, is in agreement
with previous work and does not exceed the expected observational errors.
Previous work suggested an internal metallicity spread only when fainter
samples of stars were considered, so we cannot exclude the possibility of an
intrinsic metallicity dispersion in NGC 5824. The M2FS spectra reveal a large
internal dispersion in [Mg/Fe], 0.28 dex, which is found in a few other
luminous, metal-poor clusters. [Mg/Fe] is correlated with [O/Fe] and
anti-correlated with [Na/Fe] and [Al/Fe]. There is no evidence for internal
dispersion among the other alpha- or Fe-group abundance ratios. Twenty-five of
the 26 stars exhibit a n-capture enrichment pattern dominated by r-process
nucleosynthesis ([Eu/Fe]=+0.11+/-0.12; [Ba/Eu]=-0.66+/-0.05). Only one star
shows evidence of substantial s-process enhancement ([Ba/Fe]=+0.56+/-0.12;
[Ba/Eu]=+0.38+/-0.14), but this star does not exhibit other characteristics
associated with s-process enhancement via mass-transfer from a binary
companion. The Pb and other heavy elements produced by the s-process suggest a
timescale of no more than a few hundred Myr for star formation and chemical
enrichment, like the complex globular clusters M2, M22, and NGC 5286.
