Calibrating the BHB Star Distance Scale and the Halo Kinematic Distance
  to the Galactic Centre
  We report the first determination of the distance to the Galactic centre
based on the kinematics of halo objects. We apply the statistical-parallax
technique to the sample of ~2500 Blue Horizontal Branch (BHB) stars compiled by
Xue et al. (2011) to simultaneously constrain the correction factor to the
photometric distances of BHB stars as reported by those authors and the
distance to the Galactic centre to find R0=8.2+/-0.6 kpc. We also find that the
average velocity of our BHB star sample in the direction of Galactic rotation,
V0=-240+/-4 km/s, is greater by about 20 km/s in absolute value than the
corresponding velocity for halo RR Lyrae type stars (V0=-222+/-4 km/s) in the
Galactocentric distance interval from 6 to 18 kpc, whereas the total (sigma V)
and radial (sigma r) velocity dispersion of the of the BHB sample are smaller
by about 40-45 km/s than the corresponding parameters of the velocity
dispersion ellipsoid of halo RR Lyrae type variables. The velocity dispersion
tensor of halo BHB stars proved to be markedly less anisotropic than the
corresponding tensor for RR Lyrae type variables: the corresponding anisotropy
parameter values are equal to beta(BHB)=0.51+/-0.02 and beta(RR)=0.71+/-0.03,
respectively.
