Helium burning and neutron sources in the stars

Abstract.

Helium burning represents an important stage of stellar evolution as it contributes to the synthesis of key elements such as carbon, through the triple-$\alpha$ process, and oxygen, through the ¹²C($\alpha$,$\gamma$)¹⁶O reaction. It is the ratio of carbon to oxygen at the end of the helium burning stage that governs the following phases of stellar evolution leading to different scenarios depending on the initial stellar mass. In addition, helium burning in Asymptotic Giant Branch stars, provides the two main sources of neutrons, namely the ¹³C($\alpha$, n)¹⁶O and the ²²Ne($\alpha$, n)²⁵Mg, for the synthesis of about half of all elements heavier than iron through the s-process. Given the importance of these reactions, much experimental work has been devoted to the study of their reaction rates over the last few decades. However, large uncertainties still remain at the energies of astrophysical interest which greatly limit the accuracy of stellar models predictions. Here, we review the current status on the latest experimental efforts and show how measurements of these important reaction cross sections can be significantly improved at next-generation deep underground laboratories.