Network calculations for cosmochronometric studies

Abstract

The determinations of the age of the oldest objects in the universe, giving a lower limit of the age of the universe itself, are of great
interest in astrophysics and cosmology. With the detection of the long-lived isotopes of thorium and uranium in a single star, their
application as cosmochronometers has become possible. With network calculations, the production of Th and U can be studied for
different input of the underlying mass model and the astrophysical environment. A comparison with the abundance pattern of very
metal-poor stars can serve as a reference to check the validity of the assumptions and to better understand their influences on the
final outcomes of the calculations. Once the initial amount of thorium and uranium are known, age estimations of stellar objects can
be accomplished. Network calculations were performed that allow flexibly changing and studying the astrophysical environment in
a parametric way, as well as the underlying nuclear physics input in terms of the final abundance pattern. The network used here
includes more than 7000 nuclei, reaching far outside in the neutron rich area. The most relevant fission processes were implicitly
taken into account. For all three massmodels a good agreement between the final abundance pattern and the abundance distribution
for six metal poor stars is demonstrated. Network calculations are thus an appropriate tool to study and analyze the production of
the cosmochronometers Th and U, which can be used for age-determinations for stars. A more detailed study of their production
paths is necessary to reduce uncertainties with respect to the underlying massmodel and astrophysical environment.