Introduction to Asymptotic Giant Branch Stars and their Significance

Abstract

A compact review of the main characteristics of asymptotic giant branch stars (briefly: AGB) will be described. We describe a link with observations and basic features of theoretical modeling of these important evolutionary phases of these stars.

The AGB stars are the progenitors of white dwarfs in the galaxy, and they produce about half of the heavy elements and their isotopes beyond iron element via the s-process nucleosynthesis, which is a slow neutron-capture process linked to \(\beta\) radioactive decay. The essential neutron source is mainly due to the ¹³C(\(\alpha\),n)¹⁶O reaction, and to a lesser extent the ²²Ne(\(\alpha\),n)²⁵Mg reaction. In addition, several important elements are produced such as ¹⁹ F and ²⁷ Al during the thermal pulsation of the  stars. The summary in sect. 6 contains the most important aspects of the AGBs. It is a challenging astrophysical problem to describe the process of convective mixing coupled to nuclear reactions during thermal pulsations including the effect of the magnetic field to obtain the right amount of ¹³ C that can lead to _s process abundances compatible with observation. Important remaining problems are presented in the present work.