Discovery of the host cluster for the fundamental Cepheid calibrator Zeta Geminorum

Abstract

New and existing CORAVEL, UBVJHK_s, HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that the fundamental Cepheid calibrator ζ Gem is a cluster member. The following parameters were inferred for ζ 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 τ = 7.85±0.15, and d = 355±15 pc. The mean distance to ζ Gem from cluster membership and six recent estimates (e.g., IRSB) is d = 363 ± 9(σ_x̄) ± 26(σ) pc.The results presented here support the color-excess and HST parallax derived for the Cepheid by Benedict et al. 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.