Absolute magnitudes and kinematic parameters of the subsystem of RR Lyrae variables

Abstract

The statistical parallax technique is applied to a sample of 262 RRab Lyrae variables with published photoelectric photometry, metallicities, and radial velocities and with measured absolute proper motions. Hipparcos, PPM, NPM, and the Four-Million Star Catalog (Volchkov et al. 1992) were used as the sources of proper motions; the proper motions from the last three catalogs were reduced to the Hipparcos system. We determine parameters of the velocity distribution for halo [(U 0, V 0, W 0) = (−9±12, −214 ±10, − 10, −16±7) km s −1 and (σ U , σ V , σ W ) = (164±11, 105±7, 95±7) km s −1] and thick-disk [(U 0, V 0, W 0) = (−16±8, −41±7, −18±5) km s −1], and [(σ U , σ V , σ W ) = (53±9, 42±8, 26±5) km s −1] RR Lyrae, as well as the intensity-averaged absolute magnitude for RR Lyrae of these populations: 〈M V 〉 = 0.77 ± 0.10 and 〈M V 〉 = +1.11 ± 0.25 for the halo and thickdisk objects, respectively. The metallicity dependence of the absolute magnitude of RR Lyrae is analyzed (〈M V 〉 = (0.76 ± 0.12) + (0.26 ± 0.26) · ([Fe/H]+1.6)=1.17+0.26 · [Fe/H]). Our results are in satisfactory agreement with the ‹M V ›(RR)−[Fe/H]relation from Carney et al. (1992) (〈M V 〉(RR)=1.01+0.15·[Fe/H]) obtained by Baade-Wesselink's method. They provide evidence for a short distance scale: the LMC distance modulus and the distance to the Galactic center are 18.22±0.11 and 7.4±0.5 kpc, respectively. The zero point of the distance scale and the kinematic parameters of the RR Lyrae populations are shown to be virtually independent of the source of absolute proper motions used and of whether they are reduced to the Hipparcos system or not.