NOAO >   Observing Info >   Approved Programs >   2008A-0139

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Proposal Information for 2008A-0139


PI: Julio Chaname, Space Telescope Science Institute, jchaname@stsci.edu
Address: 3700 San Martin Dr., Baltimore, MD 21218, USA

CoI: Andrew P. Gould, The Ohio State University
CoI: Roeland van der Marel, Space Telescope Science Institute

Title: Distant Wide Binaries as Tracers of the Galactic Halo

Abstract: We propose to use halo stars with measured proper motions to explore the population of binaries farther into the Galactic halo than any previous study. This is important for the understanding of processes of star formation as well as the assembly of the Galactic halo. Among various applications, the resulting catalog will be used to probe the last remaining window of MACHO-like halo dark matter. We plan to build a sample of halo wide binaries that, free of selection biases, will also be larger and more distant than the one built from the revised NLTT catalog, the largest available today and which has proven particularly useful to address a variety of problems in Galactic astronomy. Among these, we took advantage, for the first time, of the known potential of wide binaries as powerful dynamical probes and excluded a Milky Way halo mostly composed of MACHOs with masses M > 43\msun at the standard local halo density. In this way, halo wide binaries were shown to complement the results of the microlensing campaigns. Using the SDSS and USNO-B, we select an initial sample of candidate pairs that satisfy color and proper-motion tests for binarity, and propose to measure the radial velocities of the components of these pairs in order to separate the real bound systems from the contamination due to chance alignments. MonteCarlo simulations of the Galactic halo and the existing proper- motion catalogs demonstrate that, for pairs pre-selected as above (i.e., with already a good likelihood of being actual binaries) and with (Delta) v_r~ 0, radial velocities accurate to 10-20 km/s provide 87% certainty that the two stars are indeed associated.


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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