Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009iaus..258..449f&link_type=abstract
The Ages of Stars, Proceedings of the International Astronomical Union, IAU Symposium, Volume 258, p. 449-456
Astronomy and Astrophysics
Astronomy
3
Stars: Abundances, Stars: Population Ii, Galaxy: Halo
Scientific paper
We present HE 1523-0901, a metal-poor star in which the radioactive elements Th and U could be detected. Only three stars have measured U abundances, of which HE 1523-0901 has the most confidently determined value. From comparing the stable Eu, Os, and Ir abundances with measurements of Th and U, stellar ages can be derived. Based on seven such chronometer abundance ratios, the age of HE 1523-0901 was found to be ~13 Gyr. Only an upper limit for Pb could be measured so far. Knowing all three abundances of Th, U, and Pb would provide a self-consistent test for r-process calculations. Pb is the beta- plus alpha-decay end-product of all decay chains in the mass region between Pb and the onset of dominant spontaneous fission above Th and U. Hence, in addition to Th/U also Th, U/Pb should be used to obtain a consistent picture for actinide chronometry. From recent r-process calculations within the classical “waiting-point” model, for a 13 Gyr old star we predict the respective abundance ratios of logγ(Th/U) = 0.84, logγ(Th/Pb) = -1.32 and logγ(U/Pb) = -2.16. We compare these values with the measured abundance ratios in HE 1523-0901 of logγ(Th/U) = 0.86, logγ(Th/Pb) > -1.0 and logγ(U/Pb) > -1.9. With this good level of agreement, HE 1523-0901 is already a vital probe for observational “near-field” cosmology by providing an independent lower limit for the age of the Universe.
Frebel Anna
Kratz Karl Ludwig
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