Statistics – Computation
Scientific paper
Dec 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...193.4506c&link_type=abstract
American Astronomical Society, 193rd AAS Meeting, #45.06; Bulletin of the American Astronomical Society, Vol. 30, p.1318
Statistics
Computation
Scientific paper
We have made rapid neutron-capture (i.e., r-process) nucleosynthesis calculations, employing internally consistent and physically realistic nuclear physics input (QRPA beta -decay rates and the ETFSI-Q nuclear mass model). These theoretical computations assume the classical waiting-point approximation of (n,gamma )-(gamma ,n) equilibrium and reproduce in detail both the isotopic and the elemental r-process solar system abundance distributions. These same elemental abundance predictions are compared with ground-based and HST observations of neutron-capture elements in the metal-poor halo stars: CS 22892--052, HD 115444, HD 122563 and HD 126238. The elemental abundances in all four metal-poor stars are reproduced by the theoretical calculations and are consistent with the solar r-process elemental distribution for the elements Z >= 56. These results strongly suggest, at least for those elements, that the relative elemental r-process abundances have not changed over the history of the Galaxy. This further suggests that there is one r-process site in the Galaxy, at least for the elements Z >= 56. Employing the observed stellar abundances of stable elements, in conjunction with the solar r-process abundances to constrain the calculations, predictions for the zero decay-age abundances of the radioactive elements Th and U are made. We compare these predictions with newly derived observational values in three very metal-poor halo stars: HD 115444, CS 22892--052 and HD 122563. Within the observational errors the observed ratio of [Th/Eu] is the same in both CS 22892--052 and HD 115444. Comparing with the theoretical ratio suggests an average age of approximately 13.0 +/- ~ 5 Gyr for these two very metal-poor stars, consistent with earlier radioactive age estimates and recent globular and cosmological age estimates.
Beers Timothy C.
Burles Scott
Cowan John J.
Kratz Karl Ludwig
Pfeiffer Bernd
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