Galactic Clusters with Associated Cepheid Variables. VI. Anonymous van den Bergh (C0634+031) and CV Monocerotis

Abstract

A photometric UBVIKC study, based upon a compilation of new and previously published photometry, is presented for the cluster surrounding the 5.38 day Cepheid CV Mon. Photoelectric, photographic, and CCD observations are presented for 200 stars lying within ~8' of CV Mon, and the data are used with spectroscopic observations for stars near the Cepheid to investigate the reddening and distance of cluster members. The reddening law for the cluster field is described by the relation EU - B/EB - V = 0.77, and the ratio of total to selective extinction for the dust clouds obscuring cluster stars is characterized by R = AV/EB - V = 3.20 ± 0.04 s.e. The foreground dust complex is located at a distance of ~900–1100 pc, whereas the cluster itself is 1.65 ± 0.03 kpc distant (V0 - MV = 11.08 ± 0.03 s.e.). CV Mon shares not only a spatial coincidence with cluster stars—a feature confirmed by star counts—but also a similar radial velocity and estimated age. Its derived luminosity as a cluster member is MV = -3.37 ± 0.08 s.e., and its derived space reddening is EB - V = 0.75 ± 0.02 [EB - V(B0) = 0.80 ± 0.02]. There is evidence for the presence of two background groups in the field, one lying immediately beyond the cluster (d = 1.86 ± 0.03 kpc) and a more distant group (d = 3.02 ± 0.08 kpc). The cluster itself exhibits photometric properties—upper–main-sequence dispersion and main-sequence gaps—consistent with rapid rotation for hot cluster members. Such features are common in Cepheid-age clusters.