NOAO >   Observing Info >   Approved Programs >   2001B-0274

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Proposal Information for 2001B-0274


PI: Bruce W. Carney, University of North Carolina, bruce@physics.unc.edu
Address: CB\#3255, Chapel Hill, NC 27516, USA

CoI: Inese Ivans, Astronomy Dept., Univ. of Texas
CoI: John Laird, Dept. of Phys. & Astr., Bowling Green St. Univ.
CoI: Chris Sneden, Astronomy Dept., Univ. of Texas

Title: Two or more halos? Two or more timescales?

Abstract: The Galaxy's halo may have two rather different origins: the lower halo may be related to the formation of the Galaxy's disk while the more distant, ``higher" halo may have formed independently of the Galaxy and was later accreted by it, perhaps in many separate events. Evidence for this includes some recently discovered tidal streams, and differences in chemical abundances, RR Lyrae pulsational periods, and binary frequency among stars located at different distances from the plane or whose motions carry them to different distances. We propose to explore the possible halo dichotomy chemically and with a reasonably precise surrogate chronometer: the relative abundances of r-process and s- process elements in local metal-poor dwarfs whose motions are well known. These stars' motions classify them as ``low halo" or ``high halo", while the ratio of the more rapidly-formed r-process elements compared to the slightly more slowly formed s-process elements provides us with a means of estimating the relative star formation timescales for the two populations.


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