HERBS I: Metallicity and alpha enhancement along the Galactic bulge
  minor axis
  To better understand the origin and evolution of the Milky Way bulge, we have
conducted a survey of bulge red giant branch and clump stars using the HERMES
spectrograph on the Anglo-Australian Telescope. We targeted ARGOS survey stars
with pre-determined bulge memberships, covering the full metallicity
distribution function. The spectra have signal-to-noise ratios comparable to,
and were analysed using the same methods as the GALAH survey. In this work, we
present the survey design, stellar parameters, distribution of metallicity and
alpha-element abundances along the minor bulge axis at latitudes $b$ =
$-10^{\circ}, -7.5^{\circ}$ and $-5^{\circ}$. Our analysis of ARGOS stars
indicates that the centroids of ARGOS metallicity components should be located
$\approx$0.09 dex closer together. The vertical distribution of
$\alpha$-element abundances is consistent with the varying contributions of the
different metallicity components. Closer to the plane, alpha abundance ratios
are lower as the metal-rich population dominates. At higher latitudes, the
alpha abundance ratios increase as the number of metal-poor stars increases.
However, we find that the trend of alpha-enrichment with respect to metallicity
is independent of latitude. Comparison of our results with those of GALAH DR2
revealed that for [Fe/H] $\approx -0.8$, the bulge shares the same abundance
trend as the high-$\alpha$ disk population. However, the metal-poor bulge
population ([Fe/H] $\lesssim -0.8$) show enhanced alpha abundance ratios
compared to the disk/halo. These observations point to fairly rapid chemical
evolution in the bulge, and that the metal-poor bulge population does not share
the same similarity with the disk as the more metal-rich populations.
