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.
Seminars are also held at JAC,