Genesis of the Heaviest Elements in the Milky Way Galaxy
Christopher Sneden,1*
John J. Cowan12
We review the origin and evolution of the heavy elements, those
with atomic numbers greater than 30, in the early history of the Milky
Way. There is a large star-to-star bulk scatter in the concentrations
of heavy elements with respect to the lighter metals, which suggests an
early chemically unmixed and inhomogeneous Galaxy. The relative
abundance patterns among the heavy elements are often very different
from the solar system mix, revealing the characteristics of the first
element donors in the Galaxy. Abundance comparisons among several halo
stars show that the heaviest neutron-capture elements (including barium
and heavier) are consistent with a scaled solar system rapid
neutron-capture abundance distribution, whereas the lighter such
elements do not conform to the solar pattern. The stellar abundances
indicate an increasing contribution from the slow neutron-capture
process (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.
1 Department of Astronomy and McDonald
Observatory, University of Texas, Austin, TX 78712, USA.
2 Department of Physics and Astronomy, University of
Oklahoma, Norman, OK 73019, USA.
*
To whom correspondence should be addressed. E-mail:
chris{at}verdi.as.utexas.edu
