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We present [Fe/H] and [$\alpha$/Fe] abundances, derived using spectralsynthesis techniques, for stars in M31's outer stellar halo. The 21 [Fe/H]measurements and 7 [$\alpha$/Fe] measurements are drawn from fields rangingfrom 43 to 165 kpc in projected distance from M31. We combine our measurementswith existing literature measurements, and compare the resulting sample of 23stars with [Fe/H] and 9 stars with [$\alpha$/Fe] measurements in M31's outerhalo with [$\alpha$/Fe] and [Fe/H] measurements, also derived from spectralsynthesis, in M31's inner stellar halo ($r < $26 kpc) and dSph galaxies. Thestars in M31's outer halo have [$\alpha$/Fe] patterns that are consistent withthe largest of M31's dSph satellites (And I and And VII). These abundancesprovide tentative evidence that the [$\alpha$/Fe] abundances of stars in M31'souter halo are more similar to the abundances of Milky Way halo stars than tothe abundances of stars in M31's inner halo. We also compare the spectralsynthesis-based [Fe/H] measurements of stars in M31's halo with previousphotometric [Fe/H] estimates, as a function of projected distance from M31. Thespectral synthesis-based [Fe/H] measurements are consistent with a large-scalemetallicity gradient previously observed in M31's stellar halo to projecteddistances as large as 100 kpc.

Elemental Abundances in M31: Iron and Alpha Element Abundances in M31's Outer Halo