RR Lyr variable stars are known as standard candles and useful tracers of old populations. We analyzed the data on 16 836 RR Lyr variables observed toward the Galactic bulge during the third phase of the OGLE survey (Soszyński et al., 2011, Acta Astron., 61, 1).
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 distribution of the bulge RR Lyr stars is R0=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.
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