With a few exceptions (reactions involving 2, maximum 3 nucleons for which "ab initio" calculations are viable), a nuclear fusion rate in astrophysical environments can only be estimated through direct or indirect measurements of the cross section at low energies (from tens of KeV to a few MeV). In many cases, the astrophysical S-factor, S(E), which represents the purely nuclear component of the cross-section, is extrapolated down to zero energy based on measurements available at higher energies. This extrapolation is often highly uncertain, especially in cases where the structure of the compound nucleus features resonant states near the fusion threshold (Ecm=0). This uncertainty can have a significant impact on our astrophysical knowledge, specifically regarding the physical structure of stars, their evolution, and the related nucleosynthesis. In this seminar, I will discuss the case of carbon fusion in intermediate- and high-mass stars. Intermediate-mass stars are the progenitors of the most massive white dwarfs, (those with masses close to the Chandrasekhar limit, and of electron-capture supernovae, while massive stars evolve to form a gravitationally unstable iron core and can give rise to classical core-collapse supernovae. Based on recent direct measurements of the cross-section for the primary carbon fusion reaction, 12C+12C, I will present possible astrophysical scenarios by assuming various models for the low-energy extrapolation of the astrophysical S-factor.
zoom link: https://gssi-it.zoom.us/j/81377120416?pwd=pJMzYKabBbCOidOCntxQZCwZUF0UUC.1
Meeting ID: 813 7712 0416
Passcode: 503252