| Abstract | The authors present astrometry and photographic photometry of the central region of the Ursa Minor dwarf spheroidal galaxy. These studies, based on first-epoch Hale Observatory 5 m plates, second-epoch KPNO 4 m plates, and a photoelectric and CCD sequence, provide a color-magnitude diagram to mv ≡ 20.5, slightly below the horizontal branch. The well-known features of the Ursa Minor color-magnitude diagram, namely a steep, relatively blue giant branch, and a blue horizontal branch are shown. Evidence for a small population of red horizontal-branch stars is given. The RR Lyrae variables, anomalous Cepheids, and suprahorizontal-branch stars are all likely members, although one suprahorizontal-branch "star" is believed to be a QSO. This QSO may provide a satisfactory zero-proper-motion reference frame for third-epoch plates, and permit the orbit of Ursa Minor to be usefully constrained. |
