Characterising the AGB bump and its potential to constrain mixing processes in stellar interiors

Abstract

In the 90's, theoretical studies motivated the use of the asymptotic-giant branch bump (AGBb) as a standard candle given the weak dependence between its luminosity and stellar metallicity. Because of the small size of observed asymptotic-giant branch (AGB) samples, detecting the AGBb is not an easy task. However, this is now possible thanks to the wealth of data collected by the CoRoT, Kepler, and TESS space-borne missions. It is well-know that the AGB bump provides valuable information on the internal structure of low-mass stars, particularly on mixing processes such as core overshooting during the core He-burning phase. In this context, we analysed ~ 4,000 evolved giants observed by Kepler and TESS, including red-giant branch stars and AGB stars, for which asteroseismic and spectrometric data are available. By using statistical mixture models, we detected the AGBb both in frequency at maximum oscillation power and in effective temperature. Then, we used the Modules for Experiments in Stellar Astrophysics MESA stellar evolution code to model AGB stars and match the AGBb occurrence with observations. From observations, we could derive the AGBb location in 15 bins of mass and metallicity. We noted that the higher the mass, the later the AGBb occurs in the evolutionary track, which agrees with theoretical works. Moreover, we found a slight increase of the luminosity at the AGBb when the metallicity increases, which complicates the use of the AGBb as a standard candle. By fitting those observations with stellar models, we noticed that low-mass stars (M < 1.0 $M_{\odot }$) require a small core overshooting region during the core He-burning phase. This core overshooting extent increases toward high mass, but above M > 1.5 $M_{\odot }$ we found that the AGBb location cannot be reproduced with a realistic He-core overshooting alone, and instead additional mixing processes have to be invoked.

arXiv comment20 pages, 7 figures, accepted in A&A

References in corpus (56)

• emcee: The MCMC Hammer
• The chemical composition of the Sun
• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure
• The GALAH+ Survey: Third Data Release
• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• Evolution of asymptotic giant branch stars I. Updated synthetic TP-AGB models and their basic calibration
• The APOKASC Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• The Second APOKASC Catalog: The Empirical Approach
• A Stellar Rotation Census of B Stars: from ZAMS to TAMS
• Determining global parameters of the oscillations of solar-like stars
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• On detecting the large separation in the autocorrelation of stellar oscillation times series
• Mixed modes in red giants: a window on stellar evolution
• Low-temperature gas opacity - AESOPUS: a versatile and quick computational tool
• Age dissection of the Milky Way discs: red giants in the Kepler field
• Period spacings in red giants II. Automated measurement
• Coulomb tunneling for fusion reactions in dense matter: Path integral Monte Carlo versus mean field
• Multiple Molecular Winds in Evolved Stars I. A Survey of CO(2-1) and CO(3-2) Emission from 45 Nearby AGB Stars
• The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- II: Stellar Atmospheric Parameters, Chemical Abundances and Distances
• On the reliability of mass-loss-rate estimates for AGB stars
• Imaging the circumstellar envelopes of AGB stars
• Measuring the extent of convective cores in low-mass stars using Kepler data: towards a calibration of core overshooting
• The bottleneck of the CNO burning and the age of the Globular Clusters
• Evolutionary influences on the structure of red-giant acoustic oscillation spectra from 600d of Kepler observations
• The dependence of convective core overshooting on stellar mass: Additional binary systems and improved calibration
• The dependence of convective core overshooting on stellar mass: semi-empirical determination using the diffusive approach with two different element mixtures
• Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump
• Non-radial oscillations in M-giant semi-regular variables: Stellar models and Kepler observations
• Thermohaline mixing in evolved low-mass stars
• Period-luminosity relations in evolved red giants explained by solar-like oscillations
• The dependence of convective core overshooting on stellar mass: reality check, and additional evidence
• The Age Dependent Luminosities of the Red Giant Branch Bump, Asymptotic Giant Branch Bump, and Horizontal Branch Red Clump
• Inferring mode inertias in evolved solar-like stars
• Kepler red-clump stars in the field and in open clusters: constraints on core mixing
• The Red-Giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities
• Prospects for Galactic and stellar astrophysics with asteroseismology of giant stars in the $TESS$ Continuous Viewing Zones and beyond
• Asteroseismology of luminous red giants with Kepler I: Long Period Variables with radial and non-radial modes
• Stellar convective penetration: parameterized theory and dynamical simulations
• Solar-like oscillations from the depths of the red-giant star KIC 4351319 observed with Kepler
• Pulsation-triggered dust production by asymptotic giant branch stars
• The onset of the AGB wind tied to a transition between sequences in the period-luminosity diagram
• Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints
• Modelling a high-mass red giant observed by CoRoT
• Probing the mid-layer structure of red giants I. Mixed-mode coupling factor as a seismic diagnosis
• Seismic performance
• Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation
• Impact of Convective Boundary Mixing on the TP-AGB
• Seismic constraints on the internal structure of evolved stars: From high-luminosity RGB to AGB stars
• Convective Penetration in Early-Type Stars

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