Deciphering the 3D structure of the old Galactic bulge from the OGLE RR Lyrae stars

Understand

We have analyzed a sample of 27,258 fundamental-mode RR Lyrae variable stars (type RRab) detected recently toward the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE) survey.

• The data support our earlier claim that these metal-poor stars trace closely the barred structure formed of intermediate-age red clump giants.
• The distance to the Galactic center (GC) inferred from the bulge RR Lyrae stars is R_0=8.27+/-0.01(stat)+/-0.40(sys) kpc.
• We show that their spatial distribution has the shape of a triaxial ellipsoid with an major axis located in the Galactic plane and inclined at an angle of i=20+/-3 deg to the Sun-GC line of sight.