2012ApJ...750..169P

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±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 [Fe/H]=-1.02±0.18, with a dispersion of 0.25 dex. In the inner regions (|l| < 3°,|b| < 4°) 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±0.42 kpc. We report a break in the mean density distribution at a distance of ∼0.5 kpc from the center indicating its likely flattening. Using the OGLE-III data, we assess that (4-7)x10⁴ type ab RR Lyr variables should be detected toward the bulge area of the ongoing 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.