An Expanded Chemo-dynamical Sample of Red Giants in the Bar of the Large
  Magellanic Cloud
  We report new spectroscopic observations obtained with the Michigan/Magellan
Fiber System of 308 red giants (RGs) located in two fields near the photometric
center of the bar of the Large Magellanic Cloud. This sample consists of 131
stars observed in previous studies (in one field) and 177 newly-observed stars
(in the second field) selected specifically to more reliably establish the
metallicity and age distributions of the bar. For each star, we measure its
heliocentric line-of-sight velocity, surface gravity and metallicity from its
high-resolution spectrum (effective temperatures come from photometric colors).
The spectroscopic Hertzsprung-Russell diagrams---modulo small offsets in
surface gravities---reveal good agreement with model isochrones. The mean
metallicity of the 177-RG sample is $\rm [Fe/H]=-0.76\pm0.02$ with a
metallicity dispersion $\sigma=0.28\pm0.03$. The corresponding metallicity
distribution---corrected for selection effects---is well fitted by two Gaussian
components: one metal-rich with a mean $-0.66\pm0.02$ and a standard deviation
$0.17\pm0.01$, and the other metal-poor with $-1.20\pm0.24$ and $0.41\pm0.06$.
The metal-rich and metal-poor populations contain approximately 85% and 15% of
stars, respectively. We also confirm the velocity dispersion in the bar center
decreases significantly from $31.2\pm4.3$ to $18.7\pm1.9$ km s$^{-1}$ with
increasing metallicity over the range $-2.09$ to $-0.38$. Individual stellar
masses are estimated using the spectroscopic surface gravities and the known
luminosities. We find that lower mass hence older RGs have larger metallicity
dispersion and lower mean metallicity than the higher-mass, younger RGs. The
estimated masses, however, extend to implausibly low values ($\rm \sim
0.1~M_{\odot}$) making it impossible to obtain an absolute age-metallicity or
age distribution of the bar.
