Gaia DR3 Open Cluster Cepheids: A Unified Catalog with Calibrated Period-Age and Period-Wesenheit Relations

TL;DR

This work leverages Gaia DR3 to assemble a homogeneous census of Classical Cepheids in Galactic open clusters (OC Cepheids), extending the sample to distant and long-period regimes. By cross-matching six CC catalogs with Gaia-based OC catalogs and applying rigorous astrometric and CMD-based membership with isochrone fitting, the authors refine OC ages and extinctions and recalibrate the Cepheid PAR and PWR. They report 110 CCs in 102 OCs, of which 41 CCs in 37 OCs are reliable OC Cepheids (with 4 new identifications) and provide updated PAR and PWR relations: $oxed{ ext{log Age}=(-0.595\,\pm\,0.044)\,\log P+(8.430\,\pm\,0.042)}$ and $oxed{W_G=(-3.615\,\pm\,0.083)\,\log P+(-2.379\,\pm\,0.096)}$, using cluster-averaged parallaxes to mitigate Gaia systematics. The study demonstrates improved precision in Cepheid-based distance scales and highlights the continued value of Gaia DR3 (with DR4 expected to further increase the OC Cepheid sample). These results enhance constraints on Galactic structure and stellar evolution via the PAR and PWR, with implications for extragalactic distance measurements.%

Abstract

Classical Cepheids (CCs) in Galactic open clusters (OCs) provide essential observational constraints for calibrating the period-age relation (PAR) and the period-Wesenheit relation (PWR) of CCs. However, distant and long-period OC Cepheids remain limited, while the confirmed samples still require more precise determinations of their physical properties, such as ages and extinctions. In this work, we present a comprehensive census of OC Cepheids based on an extensive sample of distant OCs from Gaia Data Release 3 (DR3). By combining astrometric and photometric membership analyses, we identified 110 CCs associated with 102 OCs, of which 41 CCs across 37 OCs were classified as OC Cepheids, while the remaining cases were considered candidate or rejected associations. Our results are consistent with previous studies, while 4 of the 41 OC Cepheids are newly reported here. Using updated cluster parameters derived from manual isochrone fitting, we primarily refined the PAR to log Age = (-0.595 $\pm$ 0.044) log P + (8.430 $\pm$ 0.042) and recalibrated the PWR to WG = (-3.615 $\pm$ 0.083) log P + (-2.379 $\pm$ 0.096). This study expands the sample of confirmed and candidate OC Cepheids. The newly longest-period confirmed OC Cepheid is BM Per (CWNU 3123) with log P = 1.36, and two newly discovered OC Cepheid candidates have distances exceeding 6 kpc. Moreover, the PAR and PWR are improved by incorporating refined OC ages and updated parallaxes, respectively.

Figures (12)

• Figure 1: Comparison of the cluster ages and extinctions obtained from the isochrone fitting with those from the literature, including CG2020, dias2021, he2022he2023, and huntemily2024. Points of different colors correspond to OCs from the respective references.
• Figure 2: CMDs of the 4 newly identified OC Cepheids are shown, including the extinction, age, and distance parameters of their host clusters: Bochum 14, Theia 358, FSR 0158 (NSVS 8389949), and CWNU 3123. In each CMD, black points represent cluster member stars, and the inset shows the spatial distribution of members in Galactic coordinates. The size of the black points indicates the membership reliability of cluster stars as reported by He23: larger points correspond to high-confidence member stars, while smaller points represent candidate members. The blue shaded region indicates the age uncertainty, while the dark blue line corresponds to the $\log{Age}$ derived from isochrone fitting. Astrometric dispersions ($\delta_\varpi$ and $\delta_{pm}$), parallax, extinction, and age values are provided in each panel.
• Figure 3: The PAR for the 41 F mode and 1O mode OC Cepheids, compared with those derived by Bono2005, Anderson2016, and zc2021. Red and blue points represent 41 OC Cepheids from this work; blue points appear in the ZC21 PAR sample, while red points are newly identified outside of ZC21. Gray filled points and open circle are candidates or rejected samples in this work that are the other part of the PAR fitting samples in ZC21. One outlier is shown as red open circle.
• Figure 4: Period-age distribution of OC Cepheid candidates and rejected samples. Red points represent OC Cepheid candidates, while black points indicate the rejected samples. The black line represents the PAR derived in this work.
• Figure 5: Comparison of OC age determinations using different PARs. The upper panels compare cluster ages and CC period distributions from CG2020, dias2021, and huntemily2024. In the lower panels, red, green and blue points represent the age residuals relative to the PAR fits from this work, Anderson2016, and zc2021, respectively. The corresponding weighted mean residuals are indicated by the red, green, and blue lines.