Evidence of structural discontinuities in the inner core of red-giant stars

Abstract

Red giants are stars in the late stages of stellar evolution. Because they have exhausted the supply of hydrogen in their core, they burn the hydrogen in the surrounding shell. Once the helium in the core starts fusing, the star enters the clump phase, which is identified as a striking feature in the color-magnitude diagram. Since clump stars share similar observational properties, they are heavily used in astrophysical studies, as probes of distance, extinction through the galaxy, galaxy density, and stellar chemical evolution. In this work, we perform the detailed observational characterization of the deepest layers of clump stars using asteroseismic data from Kepler. We find evidence for large core structural discontinuities in about 6.7% of the stars in our sample, implying that the region of mixing beyond the convective core boundary has a radiative thermal stratification. These stars are otherwise similar to the remaining stars in our sample, which may indicate that the building of the discontinuities is an intermittent phenomenon.

arXiv comment30 pages, 4 figures, 1 table

References in corpus (28)

• emcee: The MCMC Hammer
• The chemical composition of the Sun
• Modules for Experiments in Stellar Astrophysics (MESA)
• Low Temperature Opacities
• Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars
• The Second APOKASC Catalog: The Empirical Approach
• Old stellar Galactic disc in near-plane regions according to 2MASS: scales, cut-off, flare and warp
• Probing the core structure and evolution of red giants using gravity-dominated mixed modes observed with Kepler
• Galactocentric Distance With the OGLE and Hipparcos Red Clump Stars
• On detecting the large separation in the autocorrelation of stellar oscillation times series
• Theoretical amplitudes and lifetimes of non-radial solar-like oscillations in red giants
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• Period spacings in red giants II. Automated measurement
• The universal red-giant oscillation pattern; an automated determination with CoRoT data
• Giant star seismology
• DIAMONDS: a new Bayesian Nested Sampling tool. Application to Peak Bagging of solar-like oscillations
• Period spacings in red giants I. Disentangling rotation and revealing core structure discontinuities
• Testing convective-core overshooting using period spacings of dipole modes in red giants
• Bayesian peak bagging analysis of 19 low-mass low-luminosity red giants observed with Kepler
• Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump
• Structural glitches near the cores of red giants revealed by oscillations in g-mode period spacings from stellar models
• Metallicity effect on stellar granulation detected from oscillating red giants in open clusters
• Kepler red-clump stars in the field and in open clusters: constraints on core mixing
• On the red-giant luminosity bump
• Variations of the Selective Extinction Across the Galactic Bulge - Implications for the Galactic Bar
• The treatment of mixing in core helium burning models -- III. Suppressing core breathing pulses with a new constraint on overshoot
• Analytical modelling of period spacings across the HR diagram
• Seismic characterization of red giants going through the Helium-core flash

Cited by in corpus (13)

• Asteroseismic g-mode period spacings in strongly magnetic rotating stars
• Mode Mixing and Rotational Splittings: II. Reconciling Different Approaches to Mode Coupling
• Kepler meets Gaia DR3: homogeneous extinction-corrected color-magnitude diagram and binary classification
• Buoyancy glitches in pulsating stars revisited
• Near-Core Acoustic Glitches are Not Oscillatory: Consequences for Asteroseismic Probes of Convective Boundary Mixing
• In search of gravity mode signatures in main sequence solar-type stars observed by Kepler
• Benchmarking the effective temperature scale of red giant branch stellar models: the case of the metal-poor halo giant HD 122563
• The theoretical pulsation spectra of hot B subdwarfs. Static and evolutionary STELUM models
• Parametric models of core-helium-burning stars: structural glitches near the core
• Glitches in solar-like oscillating F-type stars: Possible contribution of non-linear terms
• Probing the Cores of Subdwarf B Stars: How do They Compare to Cores in Helium Core-Burning Red Giants?
• Detailed theoretical analysis of core Helium-burning stars: Mixed mode patterns I. Impact of the He-flash discontinuity and of induced semi-convection
• Co-existence of Internal Gravity Waves and Tayler-Spruit Magnetic Fields in the Radiative Core of Low-mass Stars