THE OPTICAL GRAVITATIONAL LENSING EXPERIMENT: ANALYSIS OF THE BULGE RR LYRAE POPULATION FROM THE OGLE-III DATA

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 (vertical bar l vertical bar < 3 degrees, vertical bar b vertical bar < 4 degrees) 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 similar to 0.5 kpc from the center indicating its likely flattening. Using the OGLE-III data, we assess that (4-7) x 10(4) 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.