An Estimate of the Distance to AN Ser using an RR Lyrae Period–Luminosity Relationship

Abstract The relationship between the period of a Cepheid variable star and its absolute magnitude—the Period-Luminosity, or Leavitt Law—can be used with a measurement of apparent magnitude to measure the star’s distance. RR Lyrae stars are evolved low-mass stars with shorter periods and lower luminosities than Cepheids, but they are particularly useful for estimating distances to the oldest stellar clusters. We observed the brightness of an RR Lyrae star over time using the robotic telescopes of Las Cumbres Observatory to determine its period and apparent magnitude in four bands. We used that information and theoretical period–luminosity relationships for RR Lyrae stars to determine the distance to AN Ser to be 876 ± 25 pc. Our measured distance is smaller than that modeled by GAIA DR3 via stellar parallax, BP/RP spectra, and G-band photometry (959 pc).