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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Masayuki Akiyama by email.

Wednesday 12 February at 15:00pm

"New Estimates for the Galactic Age from CS 22892-052"

Michael Hannawald (Institute for Nuclear Chemistry, University of Mainz, Germany)

Actinide chronometers have been widely used to determine ages of meteoritic samples and metal-poor stars. Another method to determine the age of the Galaxy is based on the analysis of observed abundances of long-lived r-proce r-process radionuclides (Thorium-chronometry). Based on classical r-process calculations, the age of the progenitor of the halo-star CS 22892-052 was derived as 15.6(+/-)4.6 Gyr from only a single abundance ratio of radioactive (232)Th and stable Eu in 1999. Now, with improved nuclear-data input together with new observations of 15 rare-earth elements between the A~130 and 195 r-abundance peaks and of Os and Ir in the third peak, we have tried to obtain an "element-consistent" picture of the Th-age of CS 22892-052. Furthermore, taking into account the most recent fission-barrier calculations and the estimated (beta)df-effect on the Th-age, we can obtain from the weighted average of Th/Ba-Ir in CS 22892-052 a lower limit for the Galactic age of 14.6(+/-)2.4 Gyr. From this value, it is possible to predict a (238)U abundance of log(epsiron) ~ -2.5(+0.1, -0.2) for this halo-star.

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