Abundance Clues to the Natures of the Two r-Processes

Details Abundance Clues to the Natures of the Two r-Processes Abundance Clues to the Natures of the Two r-Processes

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...20712404c&link_type=abstract

American Astronomical Society Meeting 207, #124.04; Bulletin of the American Astronomical Society, Vol. 37, p.1369

Statistics

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Scientific paper

Abundances of heavier elements (barium and beyond) in many neutron-capture-rich halo stars accurately replicate the Solar System r-process pattern. However, abundances of lighter neutron-capture elements in these stars and those of short lived nuclear radioactivities in the early Solar System appear to require contributions from two distinct types of r-process synthesis events. We examine r-process theoretical predictions to further explore the implications of the solar and stellar observations. We find that the isotopic fractions of barium, and the elemental Ba/Eu abundance ratios in r-process rich low metallicity stars can only be matched by computations in which the neutron densities are in the range 23 ≲ log nn ≲ 28. Further, our r-process calculations indicate that it is difficult to decouple production of the {2 nd}\ r-process abundance peak (A ≈ 130, including 129I) from the production of heavier elements in the barium region (A ≈ 140). For r-process conditions that successfully generate the heavy element pattern extending down to A=135, the relative abundance of 129I produced in this mass region appears to be at least 90% of the observed solar value. Finally, in the neutron number density ranges required for production of the observed solar/stellar {3 rd} r-process peak (A ≈ 200), the predicted abundances of inter-peak element hafnuim (Z = 72, A ≈ 160) follow closely those of {3 rd}-peak elements (osmium through lead). This suggests that abundance comparisons of hafnium to both rare-earth and {3 rd}-peak elements can shed further light on claims of invariance in the entire heavy end of the r-process abundance pattern.
This work has been supported in part by the National Science Foundation under grants AST 03-07279 (J.J.C.), AST 03-07495 (C.S.), and the Physics Frontier Center (JINA) PHY 02-16783 (J.W.T.), and the DOE under contract B341495 (J.W.T.). Support was also provided by the Deutsche Forschungsgemeinschaft (DFG) under contract KR 806/13-1, and the Helmholtz Gemeinschaft under grant VH-VI-061.

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