Medium-resolution Spectroscopy of Red Giant Branch Stars in $\omega$
  Centauri
  We present [Fe/H] and [Ca/Fe] of $\sim600$ red giant branch (RGB) members of
the globular cluster $\omega$ Centauri. We collect medium-resolution
($R\sim2000$) spectra using the Blanco 4 m telescope at the Cerro Tololo
Inter-American Observatory equipped with Hydra, the fiber-fed multi-object
spectrograph. We demonstrate that blending of stellar light in optical fibers
severely limits the accuracy of spectroscopic parameters in the crowded central
region of the cluster. When photometric temperatures are taken in the
spectroscopic analysis, our kinematically selected cluster members, excluding
those that are strongly affected by flux from neighboring stars, include
relatively fewer stars at intermediate metallicity ([Fe/H]$\sim-1.5$) than seen
in the previous high-resolution survey for brighter giants in Johnson &
Pilachowski. As opposed to the trend of increasing [Ca/Fe] with [Fe/H] found by
those authors, our [Ca/Fe] estimates, based on Ca II H & K measurements, show
essentially the same mean [Ca/Fe] for most of the metal-poor and
metal-intermediate populations in this cluster, suggesting that mass- or
metallicity-dependent SN II yields may not be necessary in their proposed
chemical evolution scenario. Metal-rich cluster members in our sample show a
large spread in [Ca/Fe], and do not exhibit a clear bimodal distribution in
[Ca/Fe]. We also do not find convincing evidence for a radial metallicity
gradient among RGB stars in $\omega$ Centauri.
