NOAO >   Observing Info >   Approved Programs >   2008A-0473

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Proposal Information for 2008A-0473


PI: Ricardo R. Munoz, University of Virginia, rrm8f@virginia.edu
Address: Astronomy Department, P.O. Box 400325, Charlottesville, VA 22904-4325, U.S.A.

CoI: Steven R. Majewski, University of Virginia
CoI: Jeffrey L. Carlin, University of Virginia
CoI: David L. Nidever, University of Virginia
CoI: Richard J. Patterson, University of Virginia
CoI: Kathryn V. Johnston, Columbia University

Title: Mapping of Two Newly Discovered Halo Substructures in the Grid Giant Star Survey

Abstract: It is now becoming clear that the halo of our Galaxy is coursed with streams of tidally stripped debris from satellite galaxies. These streams not only present archaeological evidence regarding the formation history of the Milky Way, but provide precise dynamical probes of the underlying mass distribution. In the course of our spectroscopic study of stars in the Grid Giant Star Survey (GGSS) using the Hydra spectrographs we have found evidence for previously unknown streams, and here we propose to obtain supplementary observations of other GGSS fields to track these dynamically found streams over greater volumes of the halo. The GGSS is a now-completed, systematically assembled catalog of photometrically identified red giant (RGB) and horizontal branch (HB) star candidates to V\lesssim17.5. Because M_V~-2, metal-poor giants at V$=$17 probe to >50 kpc, the final catalog of ~250,000 giant stars provides an unparalleled database for a study of the structure, \it substructure, and chemodynamics of the Milky Way and one that uniformly samples the entire sky. Over the past two years we have used Hydra to probe 12% of the 1302 GGSS fields to derive abundances and radial velocities for stars in these pencil beams. The GGSS field sizes, limiting magnitudes, and numbers of RGB+HB targets are well-matched to Hydra, and this has allowed us to obtain spectra of >11,000 stars in a general survey of random fields all over the sky. Among these stars are seen halo substructures both known and unknown, and we now plan to pursue a more focused survey in directions where the general survey has turned up newly discovered structures.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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