Ronald Wilhelm

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The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from(More)
The Century Survey Galactic Halo Project is a photometric and spectroscopic survey from which we select relatively blue stars (V −R < 0.30 mag) as probes of the Milky Way halo. The Survey strip spans the range of Galactic latitude 35 < b < 88, allowing us to study the nature of populations of stars and their systematic motions as a function of Galactic(More)
We describe a new RR Lyrae identification technique based on out-of-phase single-epoch photometric and spectroscopic observations contained in SDSS Data Release 6 (DR-6). This technique detects variability by exploiting the large disparity between the g − r color and the strength of the hydrogen Balmer lines when the two observations are made at random(More)
We present absolute proper motions in Kapteyn Selected Area (SA) 103. This field is located 7 west of the center of the Virgo Stellar Stream (VSS, Duffau et al. 2006), and has a well-defined main sequence representing the stream. In SA 103, we identify one RR Lyrae star as a member of the VSS, according to its metallicity, radial velocity, and distance. VSS(More)
We report on the distribution of metallicities, [Fe/H], for very metal-poor stars in the halo of the Galaxy. Although the primary information on the nature of the Metallicity Distribution Function (MDF) is obtained from the two major recent surveys for metal-poor stars, the HK survey of Beers and collaborators, and the Hamburg/ESO Survey of Christlieb and(More)
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