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 (|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)x10^4 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.
