Calibration of mixing-length parameter<i>α</i>for MLT and FST models by matching with CO<sup>5</sup>BOLD models

Sonoi, T.; Ludwig, H.‐G.; Dupret, Marc‐Antoine; Montalbán, J.; Samadi, R.; Belkacem, K.; Caffau, E.; Goupil, M. J.

doi:10.1051/0004-6361/201833495

Cited by 32 publications

(38 citation statements)

References 41 publications

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“…The mixing-length parameter was indeed found to vary with evolution and mass (e.g. Freytag et al 1999;Trampedach et al 2014;Sonoi et al 2019). Sonoi et al (2019) showed that the α CGM value can vary from 0.583 to 0.801 for stars with T eff = [4018;6725] K and log g = [1.50;4.50] dex, while the calibrated solar value was 0.69.…”

Section: Impact Of the Mixing-length Parametermentioning

confidence: 99%

“…Freytag et al 1999;Trampedach et al 2014;Sonoi et al 2019). Sonoi et al (2019) showed that the α CGM value can vary from 0.583 to 0.801 for stars with T eff = [4018;6725] K and log g = [1.50;4.50] dex, while the calibrated solar value was 0.69. For example, their computations of the mixing-length parameter for a model close to our A8 model gives α CGM = 0.636 (see their Table A.1).…”

Section: Impact Of the Mixing-length Parametermentioning

confidence: 99%

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Chemical mixing in low mass stars

Deal

Goupil

Marques

et al. 2019

A&A

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Context. When modelling stars with masses higher than 1.2 M⊙ with no observed chemical peculiarity, atomic diffusion is often neglected because, on its own, it causes unrealistic surface abundances compared with those observed. The reality is that atomic diffusion is in competition with other transport processes. Rotation is one of the processes able to prevent excessively strong surface abundance variations. Aims. The purpose of this study is to quantify the opposite or conjugated effects of atomic diffusion (including radiative acceleration) and rotationally induced mixing in stellar models of low mass stars, and to assess whether rotational mixing is able to prevent the strong abundance variations induced by atomic diffusion in F-type stars. Our second goal is to estimate the impact of neglecting both rotational mixing and atomic diffusion in stellar parameter inferences for stars with masses higher than 1.3 M⊙. Methods. Using the Asteroseismic Inference on a Massive Scale (AIMS) stellar parameter inference code, we infer the masses and ages of a set of representative artificial stars for which models were computed with the Code d’Evolution Stellaire Adaptatif et Modulaire (CESTAM; the T stands for Transport) evolution code, taking into account rotationally induced mixing and atomic diffusion, including radiative acceleration. The observed constraints are asteroseismic and classical properties. The grid of stellar models used for the optimization search include neither atomic diffusion nor rotationally induced mixing. The differences between real and retrieved parameters then provide an estimate of the errors made when neglecting transport processes in stellar parameter inference. Results. We show that for masses lower than 1.3 M⊙, rotation dominates the transport of chemical elements and strongly reduces the effect of atomic diffusion, with net surface abundance modifications similar to solar values. At higher mass, atomic diffusion and rotation are competing equally. Above 1.44 M⊙, atomic diffusion dominates in stellar models with initial rotation lower than 80 km s−1 producing a chemical peculiarity which is not observed in Kepler Legacy stars. This indicates that a transport process of chemical elements is missing, probably linked to the missing transport process of angular momentum needed to explain rotation profiles in solar-like stars. Importantly, neglecting rotation and atomic diffusion (including radiative acceleration) in the models, when inferring the parameters of F-type stars, may lead to respective errors of ≈5%, ≈2.5%, and ≈25% for stellar masses, radii, and ages. Conclusions. Atomic diffusion (including radiative acceleration) and rotational mixing should be taken into account in stellar models in order to determine accurate stellar parameters. When atomic diffusion and shellular rotation are both included, they enable stellar evolution codes to reproduce the observed metal and helium surface abundances for stars with masses up to 1.4 M⊙ at solar metallicity. However, if rotation is actually uniform for these stars (as observations seem to indicate), then an additional chemical mixing process is needed together with a revised formulation of rotational mixing. For higher masses, an additional mixing process is needed in any case.

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Section: Impact Of the Mixing-length Parametermentioning

confidence: 99%

Section: Impact Of the Mixing-length Parametermentioning

confidence: 99%

Chemical mixing in low mass stars

Deal

Goupil

Marques

et al. 2019

A&A

Self Cite

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“…In late-type stars, the entropy jump was found to decrease for increasing values of ML2/α (Magic et al 2015). This is because as convection becomes more efficient, smaller temperature gradients in the superadiabatic layers are needed to transport the same flux (Sonoi et al 2019). This relation holds for DB and DBA 1D models where the entropy minimum is located at the top of the He I convection zone (see Fig.…”

Section: Calibration Of the Entropy Jumpmentioning

confidence: 97%

“…where H p is the pressure scale height. This free parameter is not given by the MLT and instead must be calibrated from observations, which is a significant shortcoming of the theory as the particular value of the parameter can have a significant effect on the modelled structures (see examples for both evolutionary and atmospheric models : Shipman 1979;Winget et al 1982Winget et al , 1983Fontaine et al 1984;Tassoul et al 1990;Thejll et al 1991;Bergeron et al 1992;Koester et al 1994;Bergeron et al 1995;Wesemael et al 1999;Córsico & Althaus 2016), especially when convection becomes superadiabatic (Tremblay et al 2015;Sonoi et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Calibration of the mixing-length theory for structures of helium-dominated atmosphere white dwarfs

Cukanovaite

Tremblay

Freytag

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We perform a calibration of the mixing length parameter at the bottom boundary of the convection zone for helium-dominated atmospheres of white dwarfs. This calibration is based on a grid of 3D DB (pure-helium) and DBA (helium-dominated with traces of hydrogen) model atmospheres computed with the CO 5 BOLD radiationhydrodynamics code, and a grid of 1D DB and DBA envelope structures. The 3D models span a parameter space of hydrogen-to-helium abundances between −10.0 log (H/He) −2.0, surface gravities between 7.5 log g 9.0 and effective temperatures between 12 000 K T eff 34 000 K. The 1D envelopes cover a similar atmospheric parameter range, but are also calculated with different values of the mixing length parameter, namely 0.4 ML2/α 1.4. The calibration is performed based on two definitions of the bottom boundary of the convection zone, the Schwarzschild and the zero convective flux boundaries. Thus, our calibration is relevant for applications involving the bulk properties of the convection zone including its total mass, which excludes the spectroscopic technique. Overall, the calibrated ML2/α is smaller than what is commonly used in evolutionary models and theoretical determinations of the blue edge of the instability strip for pulsating DB and DBA stars. With calibrated ML2/α we are able to deduce more accurate convection zone sizes needed for studies of planetary debris mixing and dredge-up of carbon from the core. We highlight this by calculating examples of metal-rich 3D DBAZ models and finding their convection zone masses. Mixing length calibration represents the first step of in-depth investigations of convective overshoot in white dwarfs with helium-dominated atmospheres.

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“…(2). The Hopf function reads (see Sonoi et al 2019) q(τ) = 1.036−0.3134 exp(−2.448τ)−0.2959 exp(−30.0τ) . (16) In Fig.…”

Section: Intensity Fluctuations In a Grey Atmospherementioning

confidence: 99%

Velocity-intensity asymmetry reversal of solar radial p-modes

Philidet

Belkacem

Ludwig

et al. 2020

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The development of space-borne missions has significantly improved the quality of the measured spectrum of solar-like oscillators. Their p-mode line profiles can now be resolved, and their asymmetry inferred for a variety of stars other than the Sun. However, it has been known for a long time that the asymmetries of solar p-modes are reversed between the velocity and the intensity spectra. Understanding the origin of this reversal is necessary in order to use asymmetries as a tool for seismic diagnosis. Indeed, for stars other than the Sun, only the intensity power spectrum is sufficiently resolved to allow for an estimation of mode asymmetries. In Philidet et al. (2020), we developed an approach designed to model and predict these asymmetries in the velocity power spectrum of the Sun and to successfully compare them to their observationally derived counterpart. In this paper, we expand our model and predict the asymmetries featured in the intensity power spectrum. We find that the shape of the mode line profiles in intensity is largely dependent on how the oscillation-induced variations of the radiative flux are treated, and that modelling it realistically is crucial for understanding asymmetry reversal. Perturbing a solar-calibrated grey atmosphere model, and adopting the quasi-adiabatic framework as a first step, we reproduce the asymmetries observed in solar intensity spectra for low-frequency modes. We conclude that, unlike what was previously thought, it is not necessary to invoke an additional mechanism (e.g non-adiabatic effects, coherent non-resonant background signal) to explain asymmetry reversal. Such an additional mechanism is necessary, however, to explain asymmetry reversal for higher-order modes.

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Calibration of mixing-length parameterαfor MLT and FST models by matching with CO⁵BOLD models

Cited by 32 publications

References 41 publications

Chemical mixing in low mass stars

Chemical mixing in low mass stars

Calibration of the mixing-length theory for structures of helium-dominated atmosphere white dwarfs

Velocity-intensity asymmetry reversal of solar radial p-modes

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Calibration of mixing-length parameterαfor MLT and FST models by matching with CO5BOLD models

Cited by 32 publications

References 41 publications

Chemical mixing in low mass stars

Chemical mixing in low mass stars

Calibration of the mixing-length theory for structures of helium-dominated atmosphere white dwarfs

Velocity-intensity asymmetry reversal of solar radial p-modes

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Calibration of mixing-length parameterαfor MLT and FST models by matching with CO⁵BOLD models