RR Lyrae Distance Scale: Theory and Observations

Abstract

The RR Lyrae distance scale is reviewed. In particular, we discuss theoretical and empirical methods currently adopted in the literature. Moreover, we also outline pros and cons of optical and near-infrared mean magnitudes to overcome some of the problems currently affecting RR Lyrae distances. The importance of the K-band Period-Luminosity-Metallicity (PLZ _K ) relation for RR Lyrae is also discussed, together with the absolute calibration of the zero-point. We also mention some preliminary results based on NIR (J,K) time series data of the LMC cluster Reticulum. This cluster hosts a sizable sample of RR Lyrae and its distance is found to be 18.45 ± 0.04 mag using the predicted PLZ _K relation and 18.51 ± 0.06 using the PLZ _J relation. We briefly discuss the evolutionary status of Anomalous Cepheids and their possible use as distance indicators. Finally, we point out some possibilities to improve the intrinsic accuracy of theory and observations.