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

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 ${W}_{G}=(-3.06\pm 0.11)\mathrm{log}P+(-2.96\pm 0.10)$ . 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 ${W}_{G}=(-2.94\pm 0.12)\mathrm{log}P+(-2.93\pm 0.11)$ .