Gas and dust from metal-rich AGB stars

¹ INAF, Observatory of Rome, Via Frascati 33, 00077 Monte Porzio Catone (RM), Italy
e-mail: paolo.ventura@inaf.it
² Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
³ ELTE Eötvös Loránd University, Institute of Physics, Budapest 1117, Pázmány Péter sétány 1/A, Hungary
⁴ School of Physics and Astronomy, Monash University, VIC 3800, Australia
⁵ INAF, Astrophysics and Space Science Observatory, Via Piero Gobetti 93/3, 40129 Bologna, Italy
⁶ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Univ. di Padova, Vicolo dell’Osservatorio 3, Padova 35122, Italy

Received: 29 April 2020
Accepted: 29 June 2020

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.