Gas and dust from solar metallicity AGB stars

Abstract

We study the asymptotic giant branch (AGB) evolution of stars with masses between 1 M − 8.5 M . We focus on stars with a solar chemical composition, which allows us to interpret evolved stars in the Galaxy. We present a detailed comparison with models of the same chemistry, calculated with a different evolution code and based on a different set of physical assumptions. We find that stars of mass ≥ 3.5 M experience hot bottom burning at the base of the envelope. They have AGB lifetimes shorter than ∼ 3 × 10 5 yr and eject into their surroundings gas contaminated by proton-capture nucleosynthesis, at an extent sensitive to the treatment of convection. Low mass stars with 1.5 M ≤ M ≤ 3 M become carbon stars. During the final phases the C/O ratio grows to ∼ 3. We find a remarkable agreement between the two codes for the low-mass models and conclude that predictions for the physical and chemical properties of these stars, and the AGB lifetime, are not that sensitive to the modelling of the AGB phase. The dust produced is also dependent on the mass: low-mass stars produce mainly solid carbon and silicon carbide dust, whereas higher mass stars produce silicates and alumina dust. Possible future observations potentially able to add more robustness to the present results are also discussed.

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“…These include comparisons between the number of thermal pulses produced for various masses and comparison of the conditions under which the 3DU occurred (Karakas & Lattanzio 2007). Our models were broadly consistent with the literature on both accounts, producing, e.g., roughly 20-25 thermal pulses before shell exhaustion for a star with initial mass 2.0 M (Ventura et al 2018;Pignatari et al 2016;Choi et al 2016;Cristallo et al 2015;Tashibu et al 2017;Karakas & Lattanzio 2007;Blöcker 1995;Trabucchi et al 2019).…”

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“…For Pop II/I core-collapse SNe we use the yields from Bianchi & Schneider (2007) (based on the supernova models by Woosley & Weaver 1995), while for AGB stars we adopt the yields from Ferrarotti & Gail (2006a) and Zhukovska et al (2008a) (derived from the models of van den Hoek & Groenewegen 1997). However, alternative sets of consistent metal and dust yields could be adopted in future works to explore the impact of more recent calculations of core-collapse SNe (Marassi et al 2019) and AGB dust yields (Ventura et al 2012b,a;Di Criscienzo et al 2013;Dell'Agli et al 2017;Ventura et al 2018;Dell'Agli et al 2019).…”

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“…This reaction is responsible for the anticorrelation of oxygen and sodium abundances observed in globular clusters [7,8] and its rate affects models seeking to reproduce this anticorrelation; see Ref. [9] for a recent example.…”

“…There may be further consequences of the new rate on sodium production in carbon-enhanced metal poor stars, depending on the scenario of hydrogen burning [45]. Overall, the new precise nuclear physics input will be instrumental in future studies of stellar scenarios [3,9,42,43,46,47] addressing hot-bottom burning.…”