Probing the Gal. halo with RR Lyrae stars. I.

Nearly 70% of them (3642 objects) also have systemic radial velocities measured. Given the pulsating nature of RRLs, metallicity estimates are based on spectra of individual exposures that have been matched with their synthetic templates.

The systemic radial velocities are measured by fitting the observed velocity as a function of phase assuming an empirical pulsating velocity template curve. Various tests show that our analyses yield metallicities with a typical precision of 0.20dex and systemic radial velocities with uncertainties ranging from 5 to 21km/s (depending on the number of radial-velocity measurements available for a given star). Based on the well-calibrated near-infrared PM_W1_Z or PM_Ks_Z, and M_V_-[Fe/H] relations, precise distances are derived for these RRLs.