Calibrating the Cepheid Period–Wesenheit Relation in the Gaia Bands Using Galactic Open-cluster Cepheids

Abstract

Abstract Establishing the period–Wesenheit relation requires independent and accurate distance measurements of classical Cepheids (DCEPs). The precise distances provided by associated open clusters independently calibrate the period–Wesenheit relations of DCEPs. 51 DCEPs associated with open clusters are compiled using the constraints of five-dimensional astrometric information. By directly using Gaia data release 3 parallaxes, the period–Wesenheit relation in the Gaia G band is calibrated as W G = ( − 3.06 ± 0.11 ) log P + ( − 2.96 ± 0.10 ) . Compared with the results derived from directly adopting the DCEP parallaxes or from using distance moduli, the Wesenheit magnitudes based on the cluster-averaged parallaxes exhibit a tighter relation with the period. Besides, there is a systematic offset between the observed Wesenheit absolute magnitudes of distant open-cluster DCEPs and their fitted magnitudes. After considering a parallax zeropoint correction, the systematic offset can be reduced, yielding a probably better period–Wesenheit relation of W G = ( − 2.94 ± 0.12 ) log P + ( − 2.93 ± 0.11 ) .