The Absolute Magnitude of RRc Variables From Statistical Parallax

TL;DR

This study provides the first direct measurement of the absolute magnitude of RRc variable stars using statistical parallax, offering new insights into their luminosity and kinematic properties.

Contribution

It presents the first definitive absolute magnitude measurement for RRc stars derived solely from statistical parallax, based on a large, high-quality sample.

Findings

M_(V,RRc) = 0.52 +/- 0.11 at [Fe/H] = -1.59

Halo and disk kinematic parameters derived from RRc data

UCAC2 proper motion errors may be overestimated by 25%

Abstract

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 247 RRc selected from the All Sky Automated Survey (ASAS) 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 (CARRS). We find that M_(V,RRc) = 0.52 +/- 0.11 at a mean metallicity of [Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars (M_(V,RRab) = 0.75 +/- 0.13 and the only direct measurement of an RRc absolute magnitude (RZ Cephei, M_(V, RRc) = 0.27 +/- 0.17). We find the bulk velocity of the halo to be (W_pi, W_theta, W_z) = (10.9,34.9,7.2) km/s in the radial, rotational and vertical directions with dispersions (sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (154.7, 103.6, 93.8) km/s. For the disk, we find (W_pi, W_theta, W_z) = (8.5, 213.2, -22.1) km/s with dispersions (sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (63.5, 49.6, 51.3) km/s. Finally, we suggest that UCAC2 proper motion errors may be overestimated by about 25%