NuGrid stellar data set – III. Updated low-mass AGB models and s-process nucleosynthesis with metallicities Z= 0.01, Z = 0.02, and Z = 0.03

Abstract

The production of the neutron-capture isotopes beyond iron that we observe today in the Solar system is the result of the combined contribution of the r-process, the s-process, and possibly the i-process. Low-mass asymptotic giant branch (AGB) (1.5 < M/M⊙ < 3) and massive (M > 10 M⊙) stars have been identified as the main site of the s-process. In this work we consider the evolution and nucleosynthesis of low-mass AGB stars. We provide an update of the NuGrid Set models, adopting the same general physics assumptions but using an updated convective-boundary-mixing model accounting for the contribution from internal gravity waves. The combined data set includes the initial masses MZAMS/M⊙ = 2, 3 for Z = 0.03, 0.02, 0.01. These new models are computed with the mesa stellar code and the evolution is followed up to the end of the AGB phase. The nucleosynthesis was calculated for all isotopes in post-processing with the NuGrid mppnp code. The convective-boundary-mixing model leads to the formation of a 13C-pocket three times wider compared to the one obtained in the previous set of models, bringing the simulation results now in closer agreement with observations. Using these new models, we discuss the potential impact of other processes inducing mixing, like rotation, adopting parametric models compatible with theory and observations. Complete yield data tables, derived data products, and online analytic data access are provided.

Reevaluation of the Ne22(α,γ)Mg26 and Adsley1, Battino2, Best3 et al. 2021Phys. Rev. C460310View full textAdd to dashboardCite

“…We re-computed the s-process nucleosynthesis for stellar models of 2 and 3M adopting our new evaluations for 22 Ne(α,n) 25 Mg and 22 Ne(α,γ) 26 Mg reaction rates using two different codes: the stellar models computed with the MESA code [34] presented by Battino et al [35] and the NEWTON code [4] presented by Trippella et al [36]. In Figures 4 and 5 we compare our results concerning Rb abundances as a function of the total s-process abundances observed through the spectroscopy of carbon stars [37,38] of initial metal content similar to our models (Z = 0.02 and Z=0.03).…”

“…In Figures 4 and 5 we compare our results concerning Rb abundances as a function of the total s-process abundances observed through the spectroscopy of carbon stars [37,38] of initial metal content similar to our models (Z = 0.02 and Z=0.03). The M3.z3m2-hCBM model computed by Battino et al [35] are reported in Figure 4 while Figure 5 reports the comparison of the NEWTON code output with observations. In both cases, we include the results obtained adopting the reaction rates of Longland et al [5] and the rates evaluated in the present work without the Texas A&M results.…”

“…FIG.4. Rb abundances as a function of s-process abundances -results obtained using the MESA models of Battino et al[35] compared to spectroscopy. A zoomed picture is presented in the lower panel.…”

Asymptotic Giant Branch Stars and presolar grains

“…We mention, in particular, those invoking diffusive processes (like thermohaline mixing, see [24]) and those based on more rapid, oscillatory or wave-like mechanisms. These last were soon revealed to be much more effective [25,26] and actually offer now the most widely debated scenarios. These same models also provide estimates for the extension of the 13 C reservoir (or pocket, as it is often called), where s-process nucleosynthesis occurs.…”

“…Discovery of anomalous abundances in certain isotopes that are daughters of radioactive nuclei involved several elements in the last decades of the 20th century [3,4]. Among other amazing findings, they led to the realization that the n-deficient isotope of Al, 26 Al, had been present in the ESS in a huge and uniform concentration ( 26 Al/ 27 Al 5 • 10 −5 ), sufficient to affect significantly, or even control, the heating of ancient materials, which induced the early differentiation of planetary embryos [5,6]. The presence in the ESS of live radioactive isotopes from various stellar sources (whose decay products, signalling their earlier existence, are often called fossil radioactivities) was since then the object of intense research [7][8][9][10].…”