The Baade-Wesselink method and the distances to RR Lyrae stars. VI - The field stars RS Bootis, TW Herculis, VY Serpentis, and UU Virginis, and the absolute magnitudes of RR Lyrae stars

Simultaneous BVK photometry and radial velocities from high-resolution spectroscopy are used to derive distances and absolute magnitudes for three metal-rich RR Lyrae stars: RS Boo, TW Her, and UU Vir, using the surface brightness version of the Baade-Wesselink method. New K photometry and previously published optical photometry and radial velocities are used to perform the same analysis upon the extreme velocity metal-poor RR Lyrae variable VY Ser. The results of other determinations of (MV)RR are critically reevaluated to see whether RR Lyrae stars are less luminous than 0.6 mag. The results support the recent proposal that there may be a simple period-(MK) relation that is independent of metallicity and temperature effects. Such a relationship would provide an improved estimate for the distance to the Galactic center or for any high-reddening region. The age of the RR Lyrae-rich globular cluster M5 is estimated at (18 + or - 3) x 10 to the 9th yr.