Search for Classical Cepheids in Galactic Open Clusters and Calibration of the Period Wesenheit Metallicity Relation in the Gaia Bands

TL;DR

This study calibrates the period Wesenheit metallicity relation for classical Cepheids using Gaia DR3 data, enabling improved distance measurements and consistency with geometric distance estimates.

Contribution

It provides a new calibration of the PWZR using Gaia parallaxes of open cluster Cepheids, including a detailed analysis of parallax offsets and application to the LMC distance.

Findings

Calibrated the PWZR with Gaia DR3 data for 43 Cepheids.

Estimated residual parallax offsets for open clusters and field Cepheids.

Derived a LMC distance modulus consistent with geometric measurements.

Abstract

It is beneficial to calibrate the period Wesenheit metallicity relation (PWZR) of Delta Cephei stars (DCEPs), i.e., classical Cepheids, using accurate parallaxes of associated open clusters (OCs) from Gaia data release 3 (DR3). To this aim, we obtain a total of 43 OC-DCEPs (including 33 fundamental mode, 9 first overtone mode, and 1 multimode DCEPs.) and calibrate the PWZR as $W_G=(-3.356 \,\pm\, 0.033) \,(\log{P-1})+(-5.947 \,\pm\, 0.025)+(-0.285 \,\pm\, 0.064)[\textrm{Fe/H}]$. The concurrently obtained residual parallax offset in OC, $zp = -4\pm5\,\mu\textrm{as}$, demonstrate the adequacy of the parallax corrections within the magnitude range of OC member stars. By comparing the field DCEPs' DR3 parallaxes with their photometric parallaxes derived by our PWZR, we estimated the residual parallax offset in field DCEPs as $zp = -15\pm3\,\mu\textrm{as}$. Using our PWZR, we estimate the distance modulus of the Large Magellanic Cloud to be $18.482 \,\pm\, 0.040$ mag, which aligns well with the most accurate published value obtained through geometric methods.