The Metal-poor Halo of the Andromeda Spiral Galaxy (M31)

  title={The Metal-poor Halo of the Andromeda Spiral Galaxy (M31)},
  author={Jason S. Kalirai and Karoline M. Gilbert and Puragra Guhathakurta and Steven R. Majewski and James C. Ostheimer and Robert Michael Rich and Michael C. Cooper and David Brian Reitzel and Richard J. Patterson},
  journal={The Astrophysical Journal},
  pages={389 - 404}
We present spectroscopic observations of red giant branch (RGB) stars over a large expanse in the halo of the Andromeda spiral galaxy (M31), acquired with the DEIMOS instrument on the Keck II 10 m telescope. Using a combination of five photometric/spectroscopic diagnostics—(1) radial velocity, (2) intermediate-width DDO51 photometry, (3) Na I equivalent width (surface gravity-sensitive), (4) position in the color-magnitude diagram, and (5) comparison between photometric and spectroscopic [Fe/H… 
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