Nuclear Seminar

R-matrix analysis of CNO cycle reactions using AZURE

Edward Simpson
University of Surrey

Monday, September 11, 2006   4:00 p.m.   NSH 124
(Refreshments served prior to seminar in NSH 124)

 

The CNO cycle is the main process for hydrogen burning in stars somewhat more massive than the Sun. The reaction cross sections at Gamow energies are typically in the femto to pico-barn range and are consequently very difficult to measure experimentally.  The CNO reaction rates are based on extrapolations of experimental data from higher energies.  We are developing a multi-channel R-matrix code to provide a new and more comprehensive tool for fitting experimental data and making extrapolations to low energies in all reaction and scattering channels.  Developments are being made to include contributions from nonresonant (direct) reaction channels.

The ¹⁴N(p,γ)¹⁵O reaction is the slowest reaction of the CNO cycle and thus it determines the energy production rate of CNO burning.  Furthermore, this reaction plays an important role in the determination of Globular Cluster age, since the position of the turnoff, point at which the GC stars escape from the Main Sequence, is powered by the onset of the CNO burning, whose bottleneck is the ¹⁴N(p,γ)¹⁵O.  The ratio of the ¹⁵N(p,γ)¹⁶O and ¹⁵N(p,α)¹²C reactions determines how much catalytic material passes to higher CNO cycles and has an effect on the production of heavier elements, particularly ¹⁶O and ¹⁷O.  The AZURE code and the analysis of these reactions will be discussed