THE ABSOLUTE MAGNITUDE OF RRc VARIABLES FROM STATISTICAL PARALLAX

We present the first definitive measurement of the absolute magnitude of RR Lyrae c-type variable stars (RRc) determined purely from statistical parallax. We use a sample of 242 RRc variables selected from the All Sky Automated Survey for which high-quality light curves, photometry, and proper motions are available. We obtain high-resolution echelle spectra for these objects to determine radial velocities and abundances as part of the Carnegie RR Lyrae Survey. We find that MV,RRc = 0.59 ± 0.10 at a mean metallicity of [Fe/H] = –1.59. This is to be compared with previous estimates for RRab stars (MV,RRab = 0.76 ± 0.12) and the only direct measurement of an RRc absolute magnitude (RZ Cephei, MV,RRc = 0.27 ± 0.17). We find the bulk velocity of the halo relative to the Sun to be (Wπ, Wθ, Wz ) = (12.0, –209.9, 3.0) km s–1 in the radial, rotational, and vertical directions with dispersions (σWπ,σWθ,σWz) = (150.4, 106.1, 96.0) km s-1. For the disk, we find (Wπ, Wθ, Wz ) = (13.0, –42.0, –27.3) km s–1 relative to the Sun with dispersions (σWπ,σWθ,σWz) = (67.7,59.2,54.9) km s-1. Finally, as a byproduct of our statistical framework, we are able to demonstrate that UCAC2 proper-motion errors are significantly overestimated as verified by UCAC4