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.