München 2006 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 31: Kern- und Teilchen-Astrophysik
HK 31.4: Gruppenbericht
Mittwoch, 22. März 2006, 15:30–16:00, E
Abundance Clues to the Nature of Two r-Processes — •K.-L. Kratz1, B. Pfeiffer1, F. Farouqi1, J.J. Cowan2, C. Sneden3, and J.W. Truran4 — 1Inst. für Kernchemie & HGF-VISTARS, Univ. Mainz, Germany — 2Univ. of Oklahoma, USA — 3Univ. of Texas, USA — 4Univ. of Chicago, USA
Abundances of neutron-capture elements beyond Ba in several ultra-metal-poor (UMP) halo stars in the early Galaxy accurately replicate the Solar System r-process pattern, whereas the lighter elements show distinct under-abundances. This appears to require contributions from a second type of r-process synthesis event. We examine r-process model predictions to explore the nuclear and astrophysical implications of the solar and stellar observations. We find that the isotopic fractions of Ba, together with the Ba/Eu elemental abundance ratios in the UMP stars can only be matched by computations in which the neutron densities are nn > 1023 cm−3 (”main” r-process), whereas the reproduction of the lighter-element pattern requires only ”weak” r-process conditions of nn < 1023 cm−3. Further, our calculations indicate that it is difficult to decouple full production of the 2nd r-process abundance peak from the oberved full solar pattern beyond Ba. Finally, in the nn-ranges required for production for the observed solar / stellar 3rd r-process peak, our prediction of inter-peak element Hf follows closely those of the 3rd peak elements Os through Pb, Bi. This suggests that abundance comparisons of Hf to lower-Z rare-earth elements and to 3rd-peak elements, as well as to the Th, U cosmochronometers, can shed furhter light on claims of invariance in the entire heavy end of the r-process abundance pattern.