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J.J. Cowan (Univ. of Oklahoma), C. Sneden, I.I. Ivans (Univ. of Texas), S. Burles (MIT ), T.C. Beers (Mich. State Univ.), J.W. Truran (Univ. of Chicago), J.E. Lawler (Univ. of Wisconsin), F. Primas (ESO), G.M. Fuller (UCSD), B. Pfeiffer, K.-L. Kratz (Univ. of Mainz)
We have used the Hubble Space Telescope (HST), the Keck telescope and the H.J. Smith telescope to make new abundance detections of neutron-capture elements in the metal-poor halo star BD +17\circ3248. We have detected, for the first time in this star, the 3\rm rd r-process peak elements osmium, iridium and platinum, elements whose abundances can only be reliably determined using HST. We also report the first confirmed detection of gold in very metal-poor halo stars. Our observations illustrate a pattern seen in other halo stars with the abundances of the heavier neutron-capture elements, including the 3\rm rd r-process peak elements, consistent with a scaled solar system r-process distribution. The abundances of the lighter neutron-capture elements, including germanium and silver, fall below that same scaled solar r-process curve, a result similar to that seen in the ultra-metal-poor star CS~22892--052, and suggests different synthesis conditions for the lighter and heavier neutron-capture elements. Additionally, we observe a very weak feature at 3860.6 Å, which is likely to be the strong U II line at that wavelength. If it is indeed the U II line, this would mark BD +17\circ3248 as the second halo star with observable uranium. Our combined observations cover the widest range in proton number (from germanium to uranium) thus far of neutron-capture elements in metal-poor Galactic halo stars. Employing the thorium and uranium abundances in comparison with each other and with several stable elements, we determine an average cosmochronological age for BD +17\circ3248 and compare this value with that found for other metal-poor halo stars.
This research was supported by NASA STScI grant GO-08342, the NSF, DOE and the German BMBF.
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