Gas and dust from metal-rich AGB stars

Abstract

Context. Stars evolving through the asymptotic giant branch (AGB) phase provide significant feedback to their host system, which is both gas enriched in nuclear-burning products, and dust formed in their winds, which they eject into the interstellar medium. Therefore, AGB stars are an essential ingredient for the chemical evolution of the Milky Way and other galaxies. Aims. We study AGB models with super-solar metallicities to complete our vast database, so far extending from metal-poor to solar-chemical compositions. We provide chemical yields for masses in the range 1−8 M⊙ and metallicities Z = 0.03 and Z = 0.04. We also study dust production in this metallicity domain. Methods. We calculated the evolutionary sequences from the pre-main sequence through the whole AGB phase. We followed the variation of the surface chemical composition to calculate the chemical yields of the various species and model dust formation in the winds to determine the dust production rate and the total dust mass produced by each star during the AGB phase. Results. The physical and chemical evolution of the star is sensitive to the initial mass: M > 3 M⊙ stars experience hot bottom burning, whereas the surface chemistry of the lower mass counterparts is altered only by third dredge-up. The carbon-star phase is reached by 2.5−3.5 M⊙ stars of metallicity Z = 0.03, whereas all the Z = 0.04 stars (except the 2.5 M⊙) remain O-rich for the whole AGB phase. Most of the dust produced by metal-rich AGBs is in the form of silicate particles. The total mass of dust produced increases with the mass of the star, reaching ∼0.012 M⊙ for 8 M⊙ stars.

The Gaia-ESO Survey: Galactic evolution of lithium from iDR6

“…The nucleosynthesis prescriptions are the same as model MWG-11 of Romano et al (2019). For low-and intermediate-mass stars with initial masses in the range 1 ≤ m/M < 9, we adopted the yields by Ventura et al (2013Ventura et al ( , 2020 that include a proper treatment of the super-AGB phase for the most massive AGB stars. For massive stars with 13 ≤ m/M ≤ 100, we adopted the yields by Limongi & Chieffi (2018).…”

“…Because of the assumed fast evolution (see Grisoni et al 2017), coupled to negligible production of 7 Li from both massive AGB stars (Ventura et al 2000(Ventura et al , 2020 and GCRs (Romano et al 2001;Prantzos 2012) at the relevant metallicities, the abundance of 7 Li is predicted to remain almost flat during most of the thick-disc evolution (see also Guiglion et al 2016;Grisoni et al 2019). 10 Possible production or destruction of 7 Li due to extra mixing processes, such as thermohaline mixing in low-mass, bright RGB stars and stellar rotation (Charbonnel et al 2020), are not included in the adopted stellar models and yields (Ventura et al 2013(Ventura et al , 2020 2009) is indicated with the multiplication sign. The predictions of the parallel GCE model are highlighted with different colours depending on the assumptions made about 7 Li synthesis and cosmological lithium abundance.…”

“…Low-mass stars on the first ascent of the red giant branch (RGB) may also show enhanced lithium if some extra deep mixing is associated with the cool bottom processing (Sackmann & Boothroyd 1999). Although some Li-rich and very Li-rich giant stars do exist (Wallerstein & Sneden 1982;Ruchti et al 2011;Silva Aguirre et al 2014;Kirby et al 2016;Smiljanic et al 2018;Singh et al 2019;Charbonnel et al 2020;Deepak et al 2020), low-and intermediate-mass stars are unlikely to contribute significantly to the 7 Li enrichment on galactic scales (Ventura et al 2000(Ventura et al , 2020 unless some extreme assumptions are made on the effectiveness of mass loss along the giant branches that should be maximal exactly when the stars are Li-rich (Romano et al 2001;Travaglio et al 2001).…”

Group II Oxide Grains: How Massive Are Their AGB Star Progenitors?

“…Mid-infrared observations show the presence of alumina dust (amorphous Al 2 O 3 ) in the extended envelopes of O-rich AGB stars. Although only recent condensation experiments confirmed that amorphous alumina can condense in circumstellar conditions [5], intermediate mass (IM) AGB stars have been considered to be the main source of alumina dust in the galaxy for many years, starting from the first work by Onaka et al [6], to the most recent ones Dell'Agli et al [7], Ventura et al [8] (and the references therein).…”

“…In particular, group 4 silicates are overabundant compared to those of groups 1 and 2 (likely because of the injection of materials from a nearby supernova into the solar nebula [20]); while group 2 silicates are rarer than oxides. Such a lack could be accounted for by the fact that silicates are expected to form mainly in IM AGBs affected by HBB [7,8]. Left panel: oxygen isotopic ratios in presolar oxide grains.…”