Impact of Convective Boundary Mixing on the TP-AGB

Abstract

The treatment of convective boundaries remains an important source of uncertainty within stellar evolution, with drastic implications for the thermally-pulsing stars on the Asymptotic Giant Branch (AGB). Various sources are taken as motivation for the incorporation of convective boundary mixing during this phase, from s-process nucleosynthesis to hydrodynamical models. In spite of the considerable evidence in favour of the existence of convective boundary mixing on the pre-AGB evolution, this mixing is not universally included in models of TP-AGB stars. The aim of this investigation is to ascertain the extent of convective boundary mixing, which is compatible with observations when considering full evolutionary models. Additionally, we investigate a theoretical argument that has been made that momentum-driven overshooting at the base of the pulse-driven convection zone should be negligible. We show that, while the argument holds,estimations based on the picture of turbulent entrainment suggest that mixing is possible at both convective boundaries. We demonstrate that additional mixing at convective boundaries during core-burning phases prior to the thermally-pulsing Asymptotic Giant Branch has an impact on the later evolution, changing the mass range at which the third dredge-up and hot-bottom burning occur, and thus also the final surface composition. In addition, an effort has been made to constrain the efficiency of convective boundary mixing at the different convective boundaries, using observational constraints. Our study suggests a strong tension between different constraints that makes it impossible to reproduce all observables simultaneously within the framework of an exponentially decaying overshooting. This result calls for a reassessment of both the models of convective boundary mixing and the observational constraints.

Accepted for publication in MNRAS. 17 Pages, 15 Figures

References in corpus (12)

• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• Stellar Models and Yields of Asymptotic Giant Branch Stars
• Constraining the thermally-pulsing asymptotic giant branch phase with resolved stellar populations in the Small Magellanic Cloud
• Helium enrichment and Carbon-star Production in Metal-rich Populations
• On the proper use of the Schwarzschild and Ledoux criteria in stellar evolution computations
• Confronting uncertainties in stellar physics: calibrating convective overshooting with eclipsing binaries
• Lithium depletion in solar-like stars: effect of overshooting based on realistic multi-dimensional simulations
• The TP-AGB phase. Lifetimes from C and M star counts in Magellanic Cloud clusters
• Extreme value statistics for two-dimensional convective penetration in a pre-Main Sequence star
• The treatment of mixing in core helium burning models -- III. Suppressing core breathing pulses with a new constraint on overshoot
• On the Production of He, C and N by Low and Intermediate Mass Stars: A Comparison of Observed and Model-Predicted Planetary Nebula Abundances
• Convective and non-convective mixing in AGB stars

Cited by in corpus (10)

• The formation of ultra-massive carbon-oxygen core white dwarfs and their evolutionary and pulsational properties
• Calibrating Core Overshooting Parameters With Two-dimensional Hydrodynamical Simulations
• A Fresh Look at AGB stars in Galactic Open Clusters with Gaia: Impact on Stellar Models and the Initial-Final Mass Relation
• The Cooling of Massive White Dwarfs from Gaia EDR3
• Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution
• The Impact of the Third Dredge-up and Mass Loss in Shaping the Initial-Final Mass Relation of White Dwarfs
• The composition of massive white dwarfs and their dependence on the C-burning modeling
• Characterising the AGB bump and its potential to constrain mixing processes in stellar interiors
• The origin of ultramassive white dwarfs: hints from Gaia EDR3
• On the Thermally Pulsing Asymptotic Giant Branch Contribution to the Light of Nearby Disk Galaxies