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

TL;DR

This paper refines luminosity and distance measurements for Type II Cepheids and RR Lyrae variables using parallaxes and pulsation data, providing improved cosmic distance scale calibrations.

Contribution

It offers new absolute magnitude calibrations for Type II Cepheids and RR Lyrae stars based on revised parallaxes and pulsation data, enhancing distance scale accuracy.

Findings

Derived absolute magnitudes for key variables using Hipparcos and pulsation parallaxes.

Estimated the LMC distance modulus as 18.37±0.09.

Determined the Galactic Centre distance as 7.64±0.21 kpc.

Abstract

Infrared and optical absolute magnitudes are derived for the type II Cepheids kappa Pav and VY Pyx from revised Hipparcos parallaxes and for kappa Pav, V553 Cen and SW Tau from pulsation parallaxes. Phase-corrected JHK mags are given for 142 RR Lyrae variables based on 2MASS data. RR Lyrae itself is overluminous compared with LMC RR Lyraes at the classical Cepheid modulus (18.39) consistent with a prediction of Catalan and Cortes. V553 Cen and SW Tau deviate by only 0.02 mag in the mean from the Matsunaga PL(K) relation for globular cluster type II Cepheids with a zero-point based on the same LMC modulus. Comparing directly these two stars with type II Cepheids in the LMC and in the Galactic Bulge leads to an LMC modulus of 18.37\pm0.09 and a distance to the Galactic Centre of 7.64\pm 0.21kpc. Kappa Pav may be a binary. V553 Cen and SW Tau show that at optical wavelengths PL relations are wider for field stars than for those in globular clusters (abridged).