新的证据支持Keystone Calientum Delta Cephei的集群成员资格
New Evidence Supporting Cluster Membership for the Keystone Calibrator Delta Cephei
摘要：
新的和现有的UBVJHKs，光谱，NOMAD，HST，和修订HIP观测，以确定性能的三角洲Cep和它的主机星团。多方面的方法确保减少了不确定性（约2%）。δ Cep的基本参数为：E（B-V）=0.073+-0.018，log（t）=7.9+-0.1，d =272+-3（se）+-5（sd）pc。星团在B6（M*/Ms~5）附近有一个转折点，最亮的主星团成员是超巨星zeta Cep（K1.5Ib）和delta Cep。在不确定性的范围内，这两颗恒星共享共同的天体测量参数（pi，mu_ra，mu_dec，RV \sim -17 km/s），并通过星团的UBVJHK色-色和色-星等图暗示的演化轨迹与更蓝的成员联系在一起。该集群的存在是由一个早期类型的序列在颜色星等图比较字段的情况下得到支持。NOMAD数据提供了一种方法来识别潜在的集群成员（n~30）和现有样本的两倍。随着与经典造父变星（例如，δ Cep），这可能会不断促进加强银河造父变星校准和减少与H_0相关的不确定性的努力。
英文摘要：
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.
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