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K. Otsuki, G. J. Mathews (University of Notre Dame), T. Kajino, W. Aoki, S. Honda (NAO Japan)
We review recent observational and theoretical results concerning the presence of actinide nuclei on the surfaces of old halo stars and their use as an age determinant. We present evidence that the observed universality of abundances for 56 < Z < 80 elements does not imply a unique astrophysical site for the r-process or a universality of abundances of elements lighter or heavier than this range. In particular, we show that a variety of astrophysical r-process models can be constructed which reproduce the observed universal r-process curve for 56 < Z < 80 elements, yet have vastly different abundances for Z > 80 and/or Z < 56. This introduces an uncertainty into the use of the Th/Eu chronometer as a means to estimate the ages of the metal deficient stars. We do find, however, that the U/Th ratio is a robust chronometer. This is because the initial production ratio of U to Th is almost independent of the astrophysical nucleosynthesis environment. The largest remaining uncertainties in the U/Th initial production ratio are due to the input nuclear physics model. We argue that new observational data might be used to constrain these nuclear physics uncertainties.
Work supported in part the Japan Society for the Promotion of Science and the U.S. Department of Energy under Grant DE-FG02-95-ER40934.
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The author(s) of this abstract have provided an email address for comments about the abstract: otsuki@nd.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.