Helium settling in F stars: constraining turbulent mixing using observed helium glitch signature

Verma, Kuldeep Chand; Aguirre, V. Silva

doi:10.1093/mnras/stz2272

Cited by 25 publications

(14 citation statements)

References 65 publications

(91 reference statements)

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“…Whereas they make no attempt to quantitatively constrain the mixing processes, they emphasise the need to include such models in studies of stellar populations and chemical evolution. Verma & Silva Aguirre (2019) showed that the analysis of acoustic glitches in asteroseismic data can be used to constrain turbulent mixing. Their results for three Kepler targets yielded log T 0 in the range from 5.9 to 6.0, when comparing the effect on surface abundances, which is also slightly higher compared to our results.…”

Section: A164 Page 12 Of 15mentioning

confidence: 99%

The Gaia-ESO survey: 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing are at the origin of chemical abundance variations

Semenova

Bergemann

Deal

et al. 2020

A&A

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Context. Atomic diffusion and mixing processes in stellar interiors influence the structure and the surface composition of stars. Some of these processes cannot yet be modelled from the first principles, and they require calibrations. This limits their applicability in stellar models used for studies of stellar populations and Galactic evolution. Aims. Our main goal is to put constraints on the stellar structure and evolution models using new refined measurements of the chemical composition in stars of a Galactic open cluster. Methods. We used medium-resolution, 19 200 ≤ R ≤ 21 500, optical spectra of stars in the open cluster NGC 2420 obtained within the Gaia-ESO survey. The sample covers all evolutionary stages from the main sequence to the red giant branch. Stellar parameters were derived using a combined Bayesian analysis of spectra, 2MASS photometry, and astrometric data from Gaia DR2. The abundances of Mg, Ca, Fe, and Li were determined from non-local thermodynamic equilibrium (NLTE) synthetic spectra, which were computed using one-dimensional (1D) and averaged three-dimensional (3D) model atmospheres. We compare our results with a grid of Code d’Evolution Stellaire Adaptatif et Modulaire (CESTAM) stellar evolution models, which include atomic diffusion, turbulent, and rotational mixing. Results. We find prominent evolutionary trends in the abundances of Fe, Ca, Mg, and Li with the mass of the stars in the cluster. Furthermore, Fe, Mg, and Ca show a depletion at the cluster turn-off, but the abundances gradually increase and flatten near the base of the red giant branch. The abundance trend for Li displays a signature of rotational mixing on the main sequence and abrupt depletion on the sub-giant branch, which is caused by advection of Li-poor material to the surface. The analysis of abundances combined with the CESTAM model predictions allows us to place limits on the parameter space of the models and to constrain the zone in the stellar interior, where turbulent mixing takes place.

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Section: A164 Page 12 Of 15mentioning

confidence: 99%

The Gaia-ESO survey: 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing are at the origin of chemical abundance variations

Semenova

Bergemann

Deal

et al. 2020

A&A

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“…Théado et al 2005), through their impact on the equilibrium structure, in particular the suppression of near-surface convection discussed in Section 2.2. Moreover, a realistic transport of chemical elements (including atomic diffusion) currently requires the addition of a parametric turbulent diffusion coefficient in order to prevent the complete depletion of helium and metals from the surface, and reproduce surface abundances of F and A-type stars (Richer et al 2000;Richard et al 2001;Michaud et al 2011;Verma & Silva Aguirre 2019;Semenova et al 2020). Magnetic fields may also impact these competing mechanisms that are thought to be related either to mass loss or turbulence in Am stars (e.g.…”

Section: Stellar Modelsmentioning

confidence: 99%

“…When a parametrised turbulent diffusion coefficient is included in the model, we use the calibration proposed by Michaud et al (2011) to explain the surface abundances of Sirius A, which uses a reference mass M 0 = 2 × 10 −6 M (hereafter D turb,Am ). In order to test a more efficient transport (as suggested by our test of Section 5.3), we also use the parametrisation calibrated on three Kepler Legacy Ftype stars (Verma & Silva Aguirre 2019), with a reference mass of M 0 = 5 × 10 −4 M (hereafter D turb,F−Kepler ). Models are computed with the same input parameters as the models of the middle panel of Fig.…”

Section: Impact Of Chemical Element Transport Processesmentioning

confidence: 99%

Fundamental properties of a selected sample of Ap stars: Inferences from interferometric and asteroseismic constraints

Deal

Cunha

Keszthelyi

et al. 2021

A&A

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Context. Magnetic fields influence the formation and evolution of stars and impact the observed stellar properties. magnetic A-type stars (Ap stars) are a prime example of this. Access to precise and accurate determinations of their stellar fundamental properties, such as masses and ages, is crucial to understand the origin and evolution of fossil magnetic fields. Aims. We propose using the radii and luminosities determined from interferometric measurements, in addition to seismic constraints when available, to infer fundamental properties of 14 Ap stars préviously characterised. Methods. We used a grid-based modelling approach, employing stellar models computed with the CESTAM stellar evolution code, and the parameter search performed with the AIMS optimisation method. The stellar model grid was built using a wide range of initial helium abundances and metallicities in order to avoid any bias originating from the initial chemical composition. The large frequency separations (Δν) of HR 1217 (HD 24712) and α Cir (HD 128898), two rapidly oscillating Ap stars of the sample, were used as seismic constraints. Results. We inferred the fundamental properties of the 14 stars in the sample. The overall results are consistent within 1σ with previous studies, however, the stellar masses inferred in this study are higher. This trend likely originates from the broader range of chemical compositions considered in this work. We show that the use of Δν in the modelling significantly improves our inferences, allowing us to set reasonable constraints on the initial metallicity which is, otherwise, unconstrained. This gives an indication of the efficiency of atomic diffusion in the atmospheres of roAp stars and opens the possibility of characterising the transport of chemical elements in their interiors.

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“…Regions in stellar interiors where the sound speed undergoes an abrupt variation have been studied for several years in solar-type stars (e.g. Mazumdar et al 2014;García & Ballot 2019;Verma & Silva Aguirre 2019). The abrupt variation of the sound speed produces a quasi-periodic oscillatory component in the frequencies of stellar oscillations (e.g.…”

Section: Seismology Of Low-mass Stars: a Study For The Outer Convecti...mentioning

confidence: 99%

Asteroseismology of low-mass stars: the balance between partial ionisation and Coulomb interactions

Brito,

Lopes

2021

Preprint

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All cool stars with outer convective zones have the potential to exhibit stochastically excited stellar oscillations. In this work, we explore the outer layers of stars less massive than the Sun. In particular, we have computed a set of stellar models raging from 0.4 to 0.9 M ⊙ with the aim at determining the impact on stellar oscillations of two physical processes occurring in the envelopes of these stars. Namely, the partial ionisation of chemical elements and the electrostatic interactions between particles in the outer layers. We find that alongside with partial ionisation, Coulomb effects also impact the acoustic oscillation spectrum. We confirm the well-known result that as the mass of a star decreases, the electrostatic interactions between particles become relevant. We found that their impact on stellar oscillations increases with decreasing mass, and for the stars with the lowest masses (M 0.6M ⊙ ), it is shown that Coulomb effects dominate over partial ionisation processes producing a strong scatter on the acoustic modes. The influence of Coulomb interactions on the sound-speed gradient profile produces a strong oscillatory behaviour with diagnostic potential for the future.

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Helium settling in F stars: constraining turbulent mixing using observed helium glitch signature

Cited by 25 publications

References 65 publications

The Gaia-ESO survey: 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing are at the origin of chemical abundance variations

The Gaia-ESO survey: 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing are at the origin of chemical abundance variations

Fundamental properties of a selected sample of Ap stars: Inferences from interferometric and asteroseismic constraints

Asteroseismology of low-mass stars: the balance between partial ionisation and Coulomb interactions

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