The Early Formation, Evolution and Age of the Neutron-Capture Elements in the Early Galaxy

Details The Early Formation, Evolution and Age of the Neutron-Capture Elements in the Early Galaxy The Early Formation, Evolution and Age of the Neutron-Capture Elements in the Early Galaxy

2001-03-14

arxiv.org/abs/astro-ph/0103222v1

Astronomy and Astrophysics

Astrophysics

6 pages, 3 figures; To appear in the proceedings of the 20th Texas Symposium on Relativistic Astrophysics, J. C. Wheeler & H.

Scientific paper

10.1063/1.1419577

Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations demonstrate that the earliest generations of stars in the Galaxy, responsible for neutron-capture synthesis and the progenitors of the halo stars, were rapidly evolving. Abundance comparisons among several halo stars show that the heaviest neutron-capture elements (including Ba and heavier) are consistent with a scaled solar system r-process abundance distribution, while the lighter such elements do not conform to the solar pattern. These comparisons suggest two r-process sites or at least two different sets of astrophysical conditions. The large star-to-star scatter observed in the neutron-capture/iron ratios at low metallicities -- which disappears with increasing [Fe/H] -- suggests an early, chemically unmixed and inhomogeneous Galaxy. The stellar abundances indicate a change from the r-process to the slow neutron capture (i.e., s-) process at higher metallicities in the Galaxy. The detection of thorium in halo and globular cluster stars offers a promising, independent age-dating technique that can put lower limits on the age of the Galaxy.

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