ASTRONOMY COLLOQUIUM - FEBRUARY 28, 2006
Inese Ivans, Carnegie Observatories
Near-UV Observations of Low-Metallicity Stars: New Insights into Neutron-Capture Nucleosynthesis Processes
The bulk of the elements beyond the iron group are created by
neutron-capture nucleosynthesis processes. Among the isotopes are
the radioactive group of elements known as the actinides, eg. Th and
U. Due to their known radioactive decay rates, the abundances of
Th (and U) in low-metallicity stars have been employed in
nucleocosmochronology, to derive the ages of presumably some of
the oldest stars in the Galaxy, thereby setting a minimum for the age
of the Universe. Critical assumptions in the analysis of the
observations are i) the production ratios of the elements are
known, and ii) the elements under investigation arise from the same
nucleosynthetic site. Recent discussions in the literature have cast
some doubt on our knowledge of those underlying assumptions. In
this talk I will review some recent results, emphasizing those of new
observational studies that may shed some light on the
contributions from various neutron-capture sites.