A differential chemical abundance scale for the globular cluster M5
  We present LTE chemical abundances for five red giants and one AGB star in
the Galactic globular cluster (GC) M5 based on high resolution spectroscopy
using the MIKE spectrograph on the Magellan 6.5-m Clay telescope. Our results
are based on a line-by-line differential abundance analysis relative to the
well-studied red giant Arcturus. The stars in our sample that overlap with
existing studies in the literature are consistent with published values for
[Fe/H] and agree to within typically 0.04 dex for the alpha-elements. Most
deviations can be assigned to varying analysis techniques in the literature.
This strengthens our newly established differential GC abundance scale and
advocates future use of this method. In particular, we confirm a mean [Fe I/H]
of -1.33 +- 0.03 (stat.) +- 0.03 (sys.) dex and also reproduce M5's enhancement
in the alpha-elements (O,Mg,Si,Ca,Ti) at +0.4 dex, rendering M5 a typical
representative of the Galactic halo. Over-ionization of Fe I in the atmospheres
of these stars by non-LTE effects is found to be less than 0.07 dex. Five of
our six stars show O-Na-Al-Mg abundance patterns consistent with pollution by
proton-capture nucleosynthesis products.
