Primary Period-Luminosity-Relation Calibrators in the Milky Way: Cepheids and RR Lyrae Physical basis, Calibration, and Applications

Abstract

In this invited review I discuss the calibration and applications of the period-luminosity relation of classical Cepheid and RR Lyrae stars. After a brief introduction, starting with results from Hipparcos and discussing some post-Hipparcos era developments, I focus on recent results using Gaia Data Release 3 data. I present an overview of the most recent period-luminosity relations, a discussion and some new results on Cepheids in open clusters. I also discuss the effect of reddening and that the use of Wesenheit indices is actually an oversimplification to dealing with the problem of reddening.

Invited Review at IAU symposium 376 "At the cross-roads of astrophysics and cosmology: Period-luminosity relations in the 2020s"