Network calculations for cosmochronometric studies

Physics

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 inputs 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 mass models, 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 mass model and astrophysical environment.