Bhuyan et al. investigate how metallicity affects the Leavitt Law by measuring period–luminosity relations at multiple pulsation phases for Cepheids in the Milky Way, LMC, and SMC. They find that both the PL slope and the metallicity term vary significantly with phase, especially between short- and long-period Cepheids. Although these variations average out to familiar mean-light results, the phase-dependent approach reveals where metallicity influences Cepheid brightness most strongly, offering a clearer path to improving cosmic distance measurements.

This study uses stellar evolution models to show how metallicity affects the brightness-period relation (Leavitt Law) of Cepheid stars. The authors find that lower-metallicity Cepheids have steeper and slightly brighter period-luminosity relations. Their predictions match key observational data and support current methods for measuring the Hubble constant, especially those using reddening-free magnitudes.