Examining the Relationship Between Convective Core Overshoot and Stellar Properties Using Asteroseismology

Viani, Lucas S.; Basu, Sarbani

doi:10.3847/1538-4357/abba17

Cited by 20 publications

(21 citation statements)

References 55 publications

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“…Asteroesismology of stars oscillating in p modes and in g modes with 1.3 ≤ M ≤ 24 M has revealed the need for a wide range of convective boundary mixing efficiencies to reproduce observed pulsation frequencies (Briquet et al 2007;Handler 2013;Moravveji et al 2016;Schmid & Aerts 2016;Szewczuk & Daszyńska-Daszkiewicz 2018;Mombarg et al 2019;Pedersen et al 2021). Additionally, asteroseismology of stars pulsating in p modes (pressure waves) between 1.15-1.5 M has revealed the need for a range of convective mixing efficiencies to reproduce observed frequencies (Deheuvels et al 2010;Deheuvels & Michel 2011;Silva Aguirre et al 2011;Salmon et al 2012;Angelou et al 2020;Viani & Basu 2020;Noll et al 2021). Similar to binaries and clusters, the modelling of pulsation frequencies (for both p and g modes) is not sensitive to the efficiency of a single mixing mechanism.…”

Section: Asteroseismologymentioning

confidence: 99%

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

Johnston

2021

Preprint

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Context. Internal chemical mixing in intermediate-and high-mass stars represents an immense uncertainty in stellar evolution models. In addition to extending the main-sequence lifetime, chemical mixing also appreciably increases the mass of the stellar core. Several studies have made attempts to calibrate the efficiency of different convective boundary mixing mechanisms, with sometimes seemingly conflicting results. Aims. We aim to demonstrate that stellar models regularly under-predict the masses of convective stellar cores. Methods. We gather convective core mass and fractional core hydrogen content inferences from numerous independent binary and asteroseismic studies, and compare them to stellar evolution models computed with the MESA stellar evolution code. Results. We demonstrate that core mass inferences from the literature are ubiquitously more massive than predicted by stellar evolution models without or with little convective boundary mixing. Conclusions. Independent of the form of internal mixing, stellar models require an efficient mixing mechanism that produces more massive cores throughout the main sequence to reproduce high-precision observations. This has implications for the post-main sequence evolution of all stars which have a well developed convective core on the main sequence.

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Section: Asteroseismologymentioning

confidence: 99%

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

Johnston

2021

Preprint

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“…They can be utilized to narrow down the range of possible parameters. It is now possible to determine that some convective boundary mixing models provide a better fit to certain asteroseismic observations than others (e.g., Viani & Basu 2020;Angelou et al 2020; Michielsen et al 2019;Pedersen et al 2018Pedersen et al , 2021, but probing the small-scale physics of the mixing is beyond the reach of even state-of-the-art asteroseismology.…”

Section: Introductionmentioning

confidence: 99%

Multidimensional low-Mach number time-implicit hydrodynamic simulations of convective helium shell burning in a massive star

Horst

Hirschi

Edelmann

et al. 2021

A&A

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Context.A realistic parametrization of convection and convective boundary mixing in conventional stellar evolution codes is still the subject of ongoing research. To improve the current situation, multidimensional hydrodynamic simulations are used to study convection in stellar interiors. Such simulations are numerically challenging, especially for flows at low Mach numbers which are typical for convection during early evolutionary stages. Aims. We explore the benefits of using a low-Mach hydrodynamic flux solver and demonstrate its usability for simulations in the astrophysical context. Simulations of convection for a realistic stellar profile are analyzed regarding the properties of convective boundary mixing. Methods. The time-implicit Seven-League Hydro (SLH) code was used to perform multidimensional simulations of convective helium shell burning based on a 25 M⊙ star model. The results obtained with the low-Mach AUSM + -up solver were compared to results when using its non low-Mach variant AUSM + B -up. We applied well-balancing of the gravitational source term to maintain the initial hydrostatic background stratification. The computational grids have resolutions ranging from 180 × 90 2 to 810 × 540 2 cells and the nuclear energy release was boosted by factors of 3 × 10 3 , 1 × 10 4 , and 3 × 10 4 to study the dependence of the results on these parameters. Results. The boosted energy input results in convection at Mach numbers in the range of 10 −3 to 10 −2 . Standard mixing-length theory (MLT) predicts convective velocities of about 1.6 × 10 −4 if no boosting is applied. The simulations with AUSM + -up show a Kolmogorov-like inertial range in the kinetic energy spectrum that extends further toward smaller scales compared with its non low-Mach variant. The kinetic energy dissipation of the AUSM + -up solver already converges at a lower resolution compared to AUSM + B -up. The extracted entrainment rates at the boundaries of the convection zone are well represented by the bulk Richardson entrainment law and the corresponding fitting parameters are in agreement with published results for carbon shell burning. However, our study needs to be validated by simulations at higher resolution. Further, we find that a general increase in the entropy in the convection zone may significantly contribute to the measured entrainment of the top boundary. Conclusion.This study demonstrates the successful application of the AUSM + -up solver to a realistic astrophysical setup. Compressible simulations of convection in early phases at nominal stellar luminosity will benefit from its low-Mach capabilities. Similar to other studies, our extrapolated entrainment rate for the helium-burning shell would lead to an unrealistic growth of the convection zone if it is applied over the lifetime of the zone. Studies at nominal stellar luminosities and different phases of the same convection zone are needed to detect a possible evolution of the entrainment rate and the impact of radiation on convective boundary mixing.

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“…Beyond the Sun, overshooting in massive stars with convective cores must be finely tuned as a function of stellar mass, again pointing to missing physics in our current parameterizations (Claret & Torres 2018;Jermyn et al 2018;Viani & Basu 2020;Martinet et al 2021;Pedersen et al 2021). Since core convective overshoot increases the reservoir of fuel available for nuclear fusion at each stage in stellar evolution, improved models of core convective boundary mixing could have profound impacts on the post-main sequence evolution and remnant formation of massive stars (Farmer et al 2019;Higgins & Vink 2020).…”

Section: Contextmentioning

confidence: 99%

Stellar convective penetration: parameterized theory and dynamical simulations

Anders,

Jermyn,

Lecoanet

et al. 2021

Preprint

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Most stars host convection zones in which heat is transported directly by fluid motion. Parameterizations like mixing length theory adequately describe convective flows in the bulk of these regions, but the behavior of convective boundaries is not well understood. Here we present 3D numerical simulations which exhibit penetration zones: regions where the entire luminosity could be carried by radiation, but where the temperature gradient is approximately adiabatic and convection is present. To parameterize this effect, we define the "penetration parameter" P which compares how far the radiative gradient deviates from the adiabatic gradient on either side of the Schwarzschild convective boundary. Following Roxburgh (1989) and Zahn (1991), we construct an energy-based theoretical model in which the extent of penetration is controlled by P. We test this theory using 3D numerical simulations which employ a simplified Boussinesq model of stellar convection. We find significant convective penetration in all simulations. Our simple theory describes the simulations well. Penetration zones can take thousands of overturn times to develop, so long simulations or accelerated evolutionary techniques are required. In stellar contexts, we expect P ≈ 1 and in this regime our results suggest that convection zones may extend beyond the Schwarzschild boundary by up to ∼20-30% of a mixing length. We present a MESA stellar model of the Sun which employs our parameterization of convective penetration as a proof of concept. We discuss prospects for extending these results to more realistic stellar contexts.

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Examining the Relationship Between Convective Core Overshoot and Stellar Properties Using Asteroseismology

Cited by 20 publications

References 55 publications

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

Multidimensional low-Mach number time-implicit hydrodynamic simulations of convective helium shell burning in a massive star

Stellar convective penetration: parameterized theory and dynamical simulations

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