Distances to high-velocity clouds

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AST-0607474INSTITUTION: University of ChicagoPI: Donald YorkTITLE: Distances to High-Velocity CloudsABSTRACTDr. Donald York (University of Chicago), along with collaborators Dr. Bastiaan Wakker (University of Wisconsin at Madison), Dr. Timothy Beers (Michigan State University), and Dr. Ronald Wilhelm (Texas Tech University), will undertake a program to determine the distances to 14 so-called high-velocity clouds (HVCs), and intermediate-velocity clouds" (IVCs). These are massive clouds of neutral hydrogen gas that are moving with velocities that are incompatible with simple models of galactic rotation. The goal will be accomplished by first determining the distances to blue horizontal branch" (BHB) stars along the line of sight from medium-resolution spectra, and then looking for interstellar absorption features from the clouds in high-resolution spectra. By determining which spectra reveal the signature of the clouds, and knowing the distances to the stars from which the spectra were derived, constraints on distances to the clouds can be obtained. Distances to these clouds remain one of the outstanding problems in Galactic astronomy, and resolution of the nature of these clouds will provide important constraints on models of galaxy formation and evolution.The work will have broad impact on various sub-fields of astronomy, particularly galaxy formation and evolution. Components of the program are self-contained, and well-suited for graduate and undergraduate research projects. Outreach activities will also be undertaken.