NOAO >   Observing Info >   Approved Programs >   2002B-0246

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Proposal Information for 2002B-0246


PI: Timothy Beers, Michigan State University, beers@pa.msu.edu
Address: E. Lansing, MI 48824, US

CoI: Norbert Christlieb, Hamburger Sternwarte, Hamburg, Germany
CoI: Jaehyon Rhee, Astronomy Dept., University of Virginia
CoI: Sean Ryan, Physics & Astronomy, Open University, UK
CoI: John Norris, Mount Stromlo & Siding Spring Obs., Australia
CoI: Silvia Rossi, IAG, University of Sao Paulo, Brazil
CoI: Tatyana Sevastyanenko, Physics & Astronomy, Michigan State University

Title: A``Quick Survey'' for Halo Giants with [Fe/H] < -2.5

Abstract: We propose to finish an accelerated search for giants in the halo of the Milky Way with [Fe/H] \le -2.5. Our primary motivation for this search are the recent discoveries of several additional ``r-process- enhanced'' stars, similar to the previously unique example of the phenomenon, CS 22892-052. These stars exhibit r-process/Fe elemental ratios in excess of 30-50 times solar values, and all possess measurable lines of the radioactive species thorium, from which lower limits of the age of the Galaxy can been made. Two of the three newly discovered r- process enhanced stars exhibit measurable U lines. However, it has also become clear that the U and Th abundances in one such star, CS 31082- 001, are about 0.4 dex \it higher than other examples of the phenomenon, indicating that our understanding of the operation of the r- process beyond the third r-process peak remains incomplete. Hence, in order to make full use of such stars for cosmochronology, substantially larger samples of these stars are required. High-resolution studies of ~ 1000 such stars, already underway with the VLT and soon to begin with SUBARU, will yield new detections of some 30 highly r-process- enhanced stars (and perhaps larger numbers of moderately r-process- enhanced stars), opening the door to detailed understanding of the r- process, as well as providing a plethora of stars useful for cosmochronology.


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