Anchors for the cosmic distance scale : the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae

Abstract

New and existing X-ray, UBVJHKsW(1−4), and spectroscopic observations were analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance because they host the classical Cepheids USgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids’ period evolution (dP/dt) from ∼140 years of observations, helped to resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, the distances derived for members of M25 and NGC7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively.