Calibrating the Cepheid Period--Wesenheit Relation in the Gaia Bands using Galactic Open Cluster Cepheids

TL;DR

This study calibrates the Cepheid period--Wesenheit relation in Gaia bands using open cluster Cepheids with Gaia DR3 data, improving the relation's accuracy and reducing systematic offsets.

Contribution

It introduces a new calibration of the period--Wesenheit relation based on open cluster Cepheids and Gaia DR3 parallaxes, enhancing precision over previous methods.

Findings

Calibrated the $W_G$ relation as $-3.06 \, \log P - 2.96$ using Gaia DR3.

Cluster-averaged parallaxes yield a tighter period--Wesenheit relation.

Applying parallax zero-point correction reduces systematic offsets.

Abstract

Establishing the period--Wesenheit relation requires independent and accurate distance measurements of classical Cepheids (DCEPs). The precise distance provided by an associated open cluster independently calibrates the period--Wesenheit relation of DCEPs. 51 DCEPs associated with open clusters are compiled using the constraints of five-dimensional astrometric information. By directly using Gaia DR3 parallax, the period--Wesenheit relation in the Gaia $G$ band is calibrated as $W_G = (-3.06 \pm 0.11) \log P + (-2.96 \pm 0.10)$. Compared with the results derived by directly adopting the DCEP parallaxes or 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 OC-DCEPs and their fitted magnitudes. After considering the parallax zero-point correction, the systematic offset can be reduced, yielding a probably better PW relation of $W_G = (-2.94 \pm 0.12) \log P + (-2.93 \pm 0.11)$.