Clues to the Metallicity Distribution in the Galactic Bulge: Abundances
  in MOA-2008-BLG310 and MOA-2008-BLG311
  We present abundance analyses based on high dispersion and high
signal-to-noise ratio Magellan spectra of two highly microlensed Galactic bulge
stars in the region of the main sequence turnoff with Teff ~ 5650 K. We find
that MOA-2008-BLG310 has [Fe/H]= +0.41 (+,- 0.09 dex) and MOA-2008-BLG311 has
+0.26 (+, - 0.09 dex). The abundance ratios for the ~20 elements for which
features could be detected in the spectra of each of the two stars follow the
trends with [Fe/H] found among samples of bulge giants. Combining these two
bulge dwarfs with the results from previous abundance analysis of four other
Galactic bulge turnoff region stars, all highly magnified by microlensing,
gives a mean [Fe/H] of +0.29dex. This implies that there there is an
inconsistency between the Fe-metallicity distribution of the microlensed bulge
dwarfs and that derived by the many previous estimates based on surveys of
cool, luminous bulge giants, which have mean [Fe/H] ~ -0.1 dex. A number of
possible mechanisms for producing this difference are discussed. If one
ascribes this inconsistency to systematic errors in the abundance analyses, we
provide statistical arguments suggesting that a substantial systematic error in
the Fe-metallicity for one or both of the two cases, bulge dwarfs vs bulge
giants, is required which is probably larger than can realistically be
accommodated.
