The kinematics and zero-point of the log P-〈MK〉 relation for Galactic RR Lyrae variables via statistical parallax

We use accurate absolute proper motions and Two-Micron All-Sky Survey Ks-band apparent magnitudes for 364 Galactic RR Lyrae variables to determine the kinematical parameters of the Galactic RR Lyrae population and constrain the zero-point of the Ks-band period–luminosity relation for these stars via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be [U0(Halo), V0(Halo), W0(Halo)]= (−12 ± 10, −217 ± 9, −6 ± 6) km s−1 and [U0(Disc), V0(Disc), W0(Disc)]= (−15 ± 7, −44 ± 7, −25 ± 5) km s−1, respectively, and the corresponding components of the velocity-dispersion ellipsoids, [σVR(Halo), σVθ(Halo), σW(Halo)]= (167 ± 9, 86 ± 6, 78 ± 5) km s−1 and [σVR(Disc), σVθ(Disc), σW(Disc)]= (55 ± 7, 44 ± 6, 30 ± 4) km s−1, respectively. The fraction of thick-disc stars is estimated at 0.25 ± 0.03. The corrected infrared period–luminosity relation is ⁠, implying a Large Magellanic Cloud (LMC) distance modulus of 18.27 ± 0.08 and a solar Galactocentric distance of 7.58 ± 0.40 kpc. Our results suggest no or slightly prograde rotation for the population of halo RR Lyraes in the Milky Way.