New Evidence Supporting Cluster Membership for the Keystone Calibrator
  Delta Cephei
  New and existing UBVJHKs, spectroscopic, NOMAD, HST, and revised HIP
observations are employed to determine properties for delta Cep and its host
star cluster. The multi-faceted approach ensured that uncertainties were
mitigated (~2%). The following fundamental parameters were inferred for delta
Cep: E(B-V)=0.073+-0.018, log(t)=7.9+-0.1, and d=272+-3(se)+-5(sd) pc. The
cluster exhibits a turnoff near B6 (M*/Ms~5), and the brightest host cluster
members are the supergiants zeta Cep (K1.5Ib) and delta Cep. To within the
uncertainties, the two stars share common astrometric parameters (pi, mu_ra,
mu_dec, RV\sim-17 km/s) and are tied to bluer members via the evolutionary
track implied by the cluster's UBVJHKs color-color and color-magnitude
diagrams. The cluster's existence is bolstered by the absence of an early-type
sequence in color-magnitude diagrams for comparison fields. NOMAD data provided
a means to identify potential cluster members (n~30) and double the existing
sample. That number could increase with forthcoming precise proper motions
(DASCH) for fainter main-sequence stars associated with classical Cepheids
(e.g., delta Cep), which may invariably foster efforts to strengthen the
Galactic Cepheid calibration and reduce uncertainties tied to H_0.
