Measurements based on a large number of red giant stars suggest a broad metallicity distribution function ( MDF ) for the Galactic bulge , centered on [ Fe / H ] \approx - 0.1 .
However , recently , a new opportunity emerged to utilize temporary flux amplification ( by factors of \sim 100 or more ) of faint dwarf stars in the Bulge that are gravitationally lensed , making them observable with high-resolution spectrographs during a short observational window .
Surprisingly , of the first 6 stars measured , 5 have [ Fe / H ] > +0.30 , suggesting a highly skewed MDF , inconsistent with observations of giant stars .
Here we present a detailed elemental abundance analysis of OGLE-2009-BLG-076S , based on a high-resolution spectrum obtained with the UVES spectrograph at the ESO Very Large Telescope .
Our results indicate it is the most metal-poor dwarf star in the Bulge yet observed , with [ Fe / H ] = -0.76 .
Our results argue against a strong selection effect disfavoring metal-poor microlensed stars .
It is possible that small number statistics is responsible for the giant/dwarf Bulge MDF discrepancy .
Should this discrepancy survive when larger numbers of Bulge dwarf stars ( soon to be available ) are analyzed , it may require modification of our understanding of either Bulge formation models , or the behavior of metal-rich giant stars .