Heavy-element yields and abundances of Asymptotic Giant Branch models with a Small Magellanic Cloud metallicity

TL;DR

This paper provides new theoretical yields and surface abundances for AGB star models at Small Magellanic Cloud metallicity, covering a range of initial masses and including detailed nucleosynthesis results for elements up to Bi.

Contribution

It introduces updated AGB stellar models with nucleosynthesis yields at SMC metallicity, including new evolutionary sequences and isotopic ratios, enhancing understanding of metal-poor stellar contributions.

Findings

Models above 1.15 M_sun become carbon-rich during AGB phase.

Hot bottom burning occurs in models with M ≥ 3.75 M_sun.

Yields and surface abundances match observations of SMC stars and presolar grains.

Abstract

We present new theoretical stellar yields and surface abundances for asymptotic giant branch (AGB) models with a metallicity appropriate for stars in the Small Magellanic Cloud (SMC, $Z= 0.0028$, [Fe/H] $\approx -0.7$). New evolutionary sequences and post-processing nucleosynthesis results are presented for initial masses between 1$M_{\odot}$ and 7$M_{\odot}$, where the 7$M_{\odot}$ is a super-AGB star with an O-Ne core. Models above 1.15$M_{\odot}$ become carbon rich during the AGB, and hot bottom burning begins in models $M \ge 3.75 M_{\odot}$. We present stellar surface abundances as a function of thermal pulse number for elements between C to Bi and for a selection of isotopic ratios for elements up to Fe and Ni (e.g., $^{12}$C/$^{13}$C), which can be compared to observations. The integrated stellar yields are presented for each model in the grid for hydrogen, helium and all stable elements from C to Bi. We present evolutionary sequences of intermediate-mass models between 4--7$M_{\odot}$ and nucleosynthesis results for three masses ($M=3.75, 5, 7M_{\odot}$) including $s$-process elements for two widely used AGB mass-loss prescriptions. We discuss our new models in the context of evolved AGB stars and post-AGB stars in the Small Magellanic Clouds, barium stars in our Galaxy, the composition of Galactic globular clusters including Mg isotopes with a similar metallicity to our models, and to pre-solar grains which may have an origin in metal-poor AGB stars.