The distance from the Sun to the centre and the shape of the old bulge in the Galaxy: 16-=221 OGLE RR Lyrae stars

A statistical method is used to determine both the Sun's distance r₀ from the Galactic Centre and the 3D structure of the old stellar population of the Galactic bulge. The space distribution of 16-=221 high latitude type-RRab RR Lyrae stars from the optical OGLE survey located towards the bulge is explored. An estimate by using RR Lyraes leads to a mean r₀ = 8.28 ± 0.14 kpc within the effective bulge radius of r_bulge = 2-3 kpc. The distribution of RR Lyraes within r_bulge has the shape of an ellipsoid slightly elongated almost towards the Sun with a major axis of its symmetry a and two minor axes b and c of about the same length. The axial ratio is a: b: c ≍ 1: 0.7: 0.7. These age-old, metal-poor, and kinematically hot stars do not trace a strong bar-like structure in the direction of the bulge at distances >1 kpc from the Galactic Centre, as b/a ∼ 1.