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

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 $M\ge 3.75M_{\odot }$. 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.

19 pages, accepted for publication in MNRAS