The Luminosities and Distance Scales of Type II Cepheid and RR Lyrae variables

Abstract

Infrared and optical absolute magnitudes are derived for the type II Cepheids κ Pav and VY Pyx using revised Hipparcos parallaxes and for κ Pav, V553 Cen and SW Tau from pulsation parallaxes. Revised Hipparcos and HST (Benedict et al.) parallaxes for RR Lyrae agree satisfactorily and are combined in deriving absolute magnitudes. Phase-corrected J, H, Ks mags are given for 142 Hipparcos RR Lyraes based on 2MASS observations. Pulsation and trigonometrical parallaxes for classical Cepheids are compared to establish the best value for the projection factor (p) used in pulsational analyses. The MV of RR Lyrae itself is 0.16 ± 0.12 mag brighter than predicted from a MV −[Fe/H] relation based RR Lyrae stars in the LMC at a modulus of 18.39 ±0.05 as found from classical Cepheids. This is consistent with the prediction of Catalan & Cortés that it is over luminous for its metallicity. The MKs results for the metaland carbon-rich, Galactic disc stars, V553 Cen and SW Tau, each with small internal