The Absolute Magnitude of RRc Variables From Statistical Parallax

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%

Submitted to ApJ. 11 pages including 6 figures

References in corpus (5)

• The Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)
• Report of the Dark Energy Task Force
• Multiperiodic Galactic field RR Lyrae stars in the ASAS catalog
• chi^2 and Linear Fits
• On the Binarity of Carbon-Enhanced, Metal-Poor Stars

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• Kinematics and Multi Band Period-Luminosity-Metallicity Relation of RR Lyrae Stars via Statistical Parallax
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• The Carnegie-Chicago Hubble Program: Calibration of the Near-Infrared RR Lyrae Period-Luminosity Relation With HST
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• The elusive chase for the first RR Lyr star in a binary system: the case of KIC 2831097