NOAO >   Observing Info >   Approved Programs >   2003A-0184

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Proposal Information for 2003A-0184


PI: Timothy Beers, Michigan State University, beers@pa.msu.edu
Address: Dept. of Physics & Astronomy, BPS 3268, E. Lansing, MI 48824, USA

CoI: Norbert Christlieb, Hamburger Sternwarte, Hamburg, Germany
CoI: Jaehyon Rhee, Astronomy Dept., Univ. of Virginia
CoI: Sean Ryan, Physics & Astronomy, Open University
CoI: Mike Bessell, Mount Stromlo & Siding Springs 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] \le -2.5

Abstract: We propose to continue our 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 (there are now \bf four known). 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 be made. Several of the newly discovered r-process enhanced stars we seek may 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 ~ 300-500 such stars, \bf already underway with the VLT (159 hours in present semester/ similar allocations expected over next 3 semesters), will yield new detections of some 10-15 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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