Estimating the Radius of the Convective Core of Main-Sequence Stars From Observed Oscillation Frequencies

Yang, Wuming

doi:10.3847/0004-637x/829/2/68

Cited by 7 publications

(7 citation statements)

References 47 publications

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“…While this is exactly the same range of values as in the 2.0 M star, we should note that for the 1.5 M star f ov = 0.005 gives a mixing rate that is only one order of magnitude larger than in the f ov = 0.01 run, indicating that the ideal value of f ov is much closer to 0.005 than to 0.01 considering that the same comparison in the 2.0 M star results in a difference of three orders of magnitude in ṀX . Asteroseismic observations by Yang (2016), on the other hand, suggest that the core of the ≈ 1.4 M Kepler star KIC 9812850 has a radius of 0.140 ± 0.028 R , which is in good agreement with the initial model of H1.5-ov1.0. This 1.5 M models also allowed us to estimate a diffusion coefficient without the need of tracer particles.…”

Section: 5msupporting

confidence: 65%

Calibrating Core Overshooting Parameters With Two-dimensional Hydrodynamical Simulations

Higl,

Mueller,

Weiss

2020

Preprint

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The extent of mixed regions around convective zones is one of the biggest uncertainties in stellar evolution. 1D overshooting descriptions introduce a free parameter ( f ov ) that is in general not well constrained from observations. Especially in small central convective regions the value is highly uncertain due to its tight connection to the pressure scale height. Long-term multi-dimensional hydrodynamic simulations can be used to study the size of the overshooting region as well as the involved mixing processes. Here we show how one can calibrate an overshooting parameter by performing 2D Maestro simulations of Zero-Age-Main-Sequence stars ranging from 1.3 to 3.5 M . The simulations cover the convective cores of the stars and a large fraction of the surrounding radiative envelope. We follow the convective flow for at least 20 convective turnover times, while the longest simulation covers 430 turnover time scales. This allows us to study how the mixing as well as the convective boundary itself evolve with time, and how the resulting entrainment can be interpreted in terms of overshooting parameters. We find that increasing the overshooting parameter f ov beyond a certain value in the initial model of our simulations, changes the mixing behaviour completely. This result can be used to put limits on the overshooting parameter. We find 0.010 < f ov < 0.017 to be in good agreement with our simulations of a 3.5M mass star. We also identify a diffusive mixing component due to internal gravity waves (IGW) that is active throughout the convectively stable layer, but most likely overestimated in our simulations. Furthermore, applying our calibration method to simulations of less massive stars suggests a need for a mass-dependent overshooting description where the mixing in terms of the pressure scale height is reduced for small convective cores.

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Section: 5msupporting

confidence: 65%

Calibrating Core Overshooting Parameters With Two-dimensional Hydrodynamical Simulations

Higl,

Mueller,

Weiss

2020

Preprint

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“…The distance of the overshooting of a convection is defined as δ ov H p , where δ ov is a free parameter and H p is the local pressure scale-height. Recently, Yang (2016b) developed a method to determine the size of the convective core including the overshooting region from observed oscillation frequencies of low-degree p-modes. It was found that the value of δ ov is variable for stars with an approximatelly equal mass.…”

Section: Introductionmentioning

confidence: 99%

The Effects of the Overshooting of the Convective Core on Main-sequence Turnoffs of Young- and Intermediate-age Star Clusters

Yang

Tian

2017

ApJ

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Recent investigations have shown that the extended main-sequence turnoffs (eMSTOs) are a common feature of intermediate-age star clusters in the Magellanic Clouds. The eMSTOs are also found in the color-magnitude diagram (CMD) of young-age star clusters. The origin of the eMSTOs is still an open question. Moreover, asteroseismology shows that the value of the overshooting parameter δ ov of the convective core is not fixed for the stars with an approximatelly equal mass. Thus the MSTO of star clusters may be affected by the overshooting of the convective core (OVCC). We calculated the effects of the OVCC with different δ ov on the MSTO of youngand intermediate-age star clusters. If δ ov varies between stars in a cluster, the observed eMSTOs of young-and intermediate-age star clusters can be explained well by the effects. The equivalent age spreads of MSTO caused by the OVCC are related to the age of star clusters and are in good agreement with observed results of many clusters. Moreover, the observed eMSTOs of NGC 1856 are reproduced by the coeval populations with different δ ov . The eMSTOs of star clusters may be relevant to the effects of the OVCC. The effects of the OVCC are similar to that of rotation in some respects. But the effects cannot result in a significant split of main sequence of young star clusters at m U 21. The presence of a rapid rotation can make the split of main sequence of young star clusters more significant.

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“…It thus can counteract the effect of enhanced diffusion on the surface helium abundance (Yang 2019), i.e., it can improve the prediction of the surface helium abundance. The effects of rotation on the low-Z models were studied by Yang & Bi (2007), Turck-Chièze et al (2010, and Yang (2016Yang ( , 2019. However, the rotating models with AGSS09 mixtures (Yang 2019) disagree with the detected neutrino fluxes of Borexino Collaboration et al (2018Collaboration et al ( , 2020.…”

Section: Introductionmentioning

confidence: 98%

“…The standard solar models (SSMs) constructed in accordance with the high metal abundances (old solar abundances, e.g., GS98) are considered to be in good agreement with the seismically inferred sound-speed and density profiles, depth, and helium abundance of the CZ, but the SSMs constructed in accordance with the low metal abundances (revised solar abundances) do not completely agree with the seismically inferred results Basu & Antia 2004;Yang & Bi 2007;Basu et al 2009;Serenelli et al 2009Serenelli et al , 2011Zhang & Li 2012) and the neutrino flux constraints Turck-Chièze et al 2010Yang 2016), which is known as the solar modeling problem or solar abundance problem (Basu et al 2015;Amarsi et al 2021;Christensen-Dalsgaard 2021;Salmon et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Rotating Solar Models in Agreement with Helioseismic Results and Updated Neutrino Fluxes

Yang

2022

ApJ

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Standard solar models (SSMs) constructed in accordance with old solar abundances are in reasonable agreement with seismically inferred results, but SSMs with new low-metal abundances disagree with the seismically inferred results. The constraints of neutrino fluxes on solar models exist in parallel with those of helioseismic results. The solar neutrino fluxes were updated by the Borexino Collaboration. We constructed rotating solar models with new low-metal abundances where the effects of enhanced diffusion and convection overshoot were included. A rotating model using OPAL opacities and the Caffau abundance scale has better sound-speed and density profiles than the SSM with the old solar abundances and reproduces the observed p-mode frequency ratios r 02 and r 13. The depth and helium abundance of the convection zone of the model agree with the seismically inferred ones at the level of 1σ. The updated neutrino fluxes are also reproduced by the model at the level of 1σ. The effects of rotation and enhanced diffusion not only improve the model’s sound-speed and density profiles but also bring the neutrino fluxes predicted by the model into agreement with the detected ones. Moreover, the calculations show that OP may underestimate opacities for the regions of the Sun with T ≳ 5 × 106 K by around 1.5%, while OPAL may underestimate opacities for the regions of the Sun with 2 × 106 K ≲ T ≲ 5 × 106 K by about 1%–2%.

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Estimating the Radius of the Convective Core of Main-Sequence Stars From Observed Oscillation Frequencies

Cited by 7 publications

References 47 publications

Calibrating Core Overshooting Parameters With Two-dimensional Hydrodynamical Simulations

Calibrating Core Overshooting Parameters With Two-dimensional Hydrodynamical Simulations

The Effects of the Overshooting of the Convective Core on Main-sequence Turnoffs of Young- and Intermediate-age Star Clusters

Rotating Solar Models in Agreement with Helioseismic Results and Updated Neutrino Fluxes

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