Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution

• Published in: arXiv.org 2021-10
• Main Authors: Trueman, T C L, Côté, B, A Yagüe López, den Hartogh, J, Pignatari, M, Soós, B, Karakas, A I, Lugaro, M
• Format: Article
• Language: English
• Subjects: Asymptotic giant branch stars; Chemical evolution; Galactic evolution; Inclusions; Metallicity; Nuclear fusion; Radioisotopes
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2110.11126

Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives \(0.1-100\) Myr existed in the early Solar System (ESS). We investigate the ESS origin of \(^{107}\)Pd, \(^{135}\)Cs, and \(^{182}\)Hf, which are produced by \(slow\) neutron captures (the \(s\)-process) in asymptotic giant branch (AGB) stars. We modelled the galactic abundances of these SLRs using the OMEGA+ galactic chemical evolution (GCE) code and two sets of mass- and metallicity-dependent AGB nucleosynthesis yields (Monash and FRUITY). Depending on the ratio of the mean life \(\tau\) of the SLR to the average length of time between the formation of AGB progenitor \(\gamma\), we calculate timescales relevant for the birth of the Sun. If \(\tau/\gamma\gtrsim2\), we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted \(^{107}\)Pd/\(^{108}\)Pd, \(^{135}\)Cs/\(^{133}\)Cs, and \(^{182}\)Hf/\(^{180}\)Hf ratios to their respective ESS ratios. The predicted \(^{107}\)Pd/\(^{182}\)Hf ratio indicates that our GCE models are missing \(9-73\%\) of \(^{107}\)Pd and \(^{108}\)Pd in the ESS. This missing component may have come from AGB stars of higher metallicity than those that contributed to the ESS in our GCE code. If \(\tau/\gamma\lesssim0.3\), we calculate instead the time (\(T_{\rm LE}\)) from the last nucleosynthesis event that added the SLRs into the presolar matter to the formation of the oldest solids in the ESS. For the 2 M\(_\odot\), \(Z=0.01\) Monash model we find a self-consistent solution of \(T_{\rm LE}=25.5\) Myr.