Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Gem

TL;DR

This paper identifies Zeta Gem as a member of a star cluster, refining its fundamental parameters and supporting previous distance measurements, thereby improving the calibration of Cepheid variables for distance scale studies.

Contribution

It establishes Zeta Gem as part of a star cluster and derives its parameters using multi-source observations, enhancing the calibration of Cepheid variables.

Findings

Zeta Gem is a cluster member with a distance of approximately 363 pc.

Derived parameters include E(B-V)=0.02 and log t=7.85.

Results support previous parallax measurements by Benedict et al. (2007).

Abstract

New and existing CORAVEL, UBVJHKs, HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that the fundamental Cepheid calibrator Zeta Gem is a cluster member. The following parameters were inferred for Zeta Gem from cluster membership and are tied to new spectral classifications (DAO) established for 26 nearby stars (e.g., HD53588/B7.5IV, HD54692/B9.5IV): E(B-V)=0.02+-0.02, log t=7.85+-0.15, and d=355+-15 pc. The mean distance to Zeta Gem from cluster membership and six recent estimates (e.g., IRSB) is d=363+-9(se)+-26(sd) pc. The results presented here support the color-excess and HST parallax derived for the Cepheid by Benedict et al. (2007). Forthcoming precise proper motions (DASCH) and Chandra/XMM-Newton observations of the broader field may be employed to identify cluster members, bolster the cluster's existence, and provide stronger constraints on the Cepheid's fundamental parameters.