The kinematics and zero-point of the log P -〈 M K 〉 relation for Galactic RR Lyrae variables via statistical parallax (original) (raw)

2009, Monthly Notices of the Royal Astronomical Society

We use accurate absolute proper motions and Two-Micron All-Sky Survey K s-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 K s-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 [U 0 (Halo), V 0 (Halo), W 0 (Halo)] = (−12 ± 10, −217 ± 9, −6 ± 6) km s −1 and [U 0 (Disc), V 0 (Disc), W 0 (Disc)] = (−15 ± 7, −44 ± 7, −25 ± 5) km s −1 , respectively, and the corresponding components of the velocity-dispersion ellipsoids, [σ V R (Halo), σ V θ (Halo), σ W (Halo)] = (167 ± 9, 86 ± 6, 78 ± 5) km s −1 and [σ V R (Disc), σ V θ (Disc), σ W (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 M K s = −2.33 log P F − 0.818 ± 0.081, 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.