We have analyzed the data on 16,836 RR Lyrae ( RR Lyr ) variables observed toward the Galactic bulge during the third phase of the Optical Gravitational Lensing Experiment ( OGLE-III ) , which took place in 2001–2009 .
Using these standard candles , we show that the ratio of total to selective extinction toward the bulge is given by R _ { I } = A _ { I } / E ( V - I ) = 1.080 \pm 0.007 and is independent of color .
We demonstrate that the bulge RR Lyr stars form a metal-uniform population , slightly elongated in its inner part .
The photometrically derived metallicity distribution is sharply peaked at \hbox { $ [ { Fe } / { H } ] $ } = -1.02 \pm 0.18 , with a dispersion of 0.25 dex .
In the inner regions ( |l| < 3 \arcdeg , |b| < 4 \arcdeg ) the RR Lyr tend to follow the barred distribution of the bulge red clump giants .
The distance to the Milky Way center inferred from the bulge RR Lyr is R _ { 0 } = 8.54 \pm 0.42 kpc .
We report a break in the mean density distribution at a distance of \sim 0.5 kpc from the center indicating its likely flattening .
Using the OGLE-III data , we assess that ( 4 – 7 ) \times 10 ^ { 4 } type ab RR Lyr variables should be detected toward the bulge area of the on going near-IR VISTA Variables in the Via Lactea ( VVV ) survey , where the uncertainty partially results from the unknown RR Lyr spatial density distribution within 0.2 kpc from the Galactic center .