N'est plus au Laboratoire.
AMARD Louis
Team: Astrophysique Stellaire
louis.amard
univ-montp2.fr
0467143415
Research Topics: - phys/phys.astr/phys.astr.sr
- sdu/sdu.astr/sdu.astr.sr
- sdu/sdu.astr
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Last scientific productions :
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Lithium depletion and angular momentum transport in solar-type stars
Author(s): Dumont T., Palacios A., Charbonnel C., Richard O., Amard L., Augustson K., Mathis S.
(Article) Published:
Astronomy & Astrophysics, vol. 646 p.A48 (2021)
DOI: 10.1051/0004-6361/202039515
Abstract: Context. Transport processes occurring in the radiative interior of solar-type stars are evidenced by the surface variation of light
elements, in particular 7Li, and the evolution of their rotation rates. For the Sun, inversions of helioseismic data indicate that the
radial profile of angular velocity in its radiative zone is nearly uniform, which implies the existence of angular momentum transport
mechanisms that are efficient over evolutionary timescales. While there are many independent transport models for angular momentum
and chemical species, there is a lack of self-consistent theories that permit stellar evolution models to simultaneously match the
present-day observations of solar lithium abundances and radial rotation profiles.
Aims. We explore how additional transport processes can improve the agreement between evolutionary models of rotating stars and
observations for 7Li depletion, the rotation evolution of solar-type stars, and the solar rotation profile.
Methods. Models of solar-type stars are computed including atomic diffusion and rotation-induced mixing with the code STAREVOL.
We explore different additional transport processes for chemicals and for angular momentum such as penetrative convection,
tachocline mixing, and additional turbulence. We constrain the resulting models by simultaneously using the evolution of the sur-
face rotation rate and 7Li abundance in the solar-type stars of open clusters with different ages, and the solar surface and internal
rotation profile as inverted from helioseismology when our models reach the age of the Sun.
Results. We show the relevance of penetrative convection for the depletion of 7Li in pre-main sequence and early main sequence
stars. The rotational dependence of the depth of penetrative convection yields an anti-correlation between the initial rotation rate and7Li depletion in our models of solar-type stars that is in agreement with the observed trend. Simultaneously, the addition of an ad hoc
vertical viscosity νadd leads to efficient transport of angular momentum between the core and the envelope during the main sequence
evolution and to solar-type models that match the observed profile of the Sun. We also self-consistently compute for the first time the
thickness of the tachocline and find that it is compatible with helioseismic estimations at the age of the Sun, but we highlight that the
associated turbulence does not allow the observed 7Li depletion to be reproduced. The main sequence depletion of 7Li in solar-type
stars is only reproduced when adding a parametric turbulent mixing below the convective envelope.
Conclusions. The need for additional transport processes in stellar evolution models for both chemicals and angular momentum in
addition to atomic diffusion, meridional circulation, and turbulent shear is confirmed. We identify the rotational dependence of the
penetrative convection as a key process. Two additional and distinct parametric turbulent mixing processes (one for angular momentum
and one for chemicals) are required to simultaneously explain the observed surface 7Li depletion and the solar internal rotation profile.
We highlight the need of additional constraints for the internal rotation of young solar-type stars and also for the beryllium abundances
of open clusters in order to test our predictions.
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Impact of stellar evolution on planetary habitability
Author(s): Gallet F., Charbonnel C., Amard L., Brun S., Palacios A., Mathis S., Bolmont E.
Conference: ASTRO FLUID 2016 (NICE, FR, 2019)
Proceedings: EAS Publications Series, vol. 82 p.59-69 (2019)
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First grids of low-mass stellar models and isochrones with self-consistent treatment of rotation From 0.2 to 1.5 M-circle dot at seven metallicities from PMS to TAMS
Author(s): Amard L., Palacios A., Charbonnel C., Gallet F., Georgy C., Lagarde N., Siess L.
(Article) Published:
Astronomy & Astrophysics, vol. 631 p.A77 (2019)
Links openAccess full text :
Ref HAL: hal-02335454_v1
DOI: 10.1051/0004-6361/201935160
Exporter : BibTex | endNote
16 citations
Abstract: Aims. We present an extended grid of state-of-the art stellar models for low-mass stars including updated physics (nuclear reaction
rates, surface boundary condition, mass-loss rate, angular momentum transport, torque and rotation-induced mixing prescriptions). We
aim at evaluating the impact of wind braking, realistic atmospheric treatment, rotation and rotation-induced mixing on the structural
and rotational evolution from the pre-main sequence to the turn-off.
Methods. Using the STAREVOL code, we provide an updated PMS grid. We compute stellar models for 7 different metallicities,
from [Fe/H] = -1 dex to [Fe/H] = +0.3 dex with a solar composition corresponding to Z = 0.0134. The initial stellar mass ranges from
0.2 to 1.5 M with extra grid refinement around one solar mass. We also provide rotating models for three different initial rotation
rates (slow, median and fast) with prescriptions for the wind braking and disc-coupling timescale calibrated on observed properties of
young open clusters. The rotational mixing includes an up-to-date description of the turbulence anisotropy in stably stratified regions.
Results. The overall behaviour of our models at solar metallicity – and its constitutive physics – is validated through a detailed
comparison with a variety of distributed evolutionary tracks. The main differences arise from the choice of surface boundary conditions
and initial solar composition. The models including rotation with our prescription for angular momentum extraction and self-consistent
formalism for angular momentum transport are able to reproduce the rotation period distribution observed in young open clusters over
a broad mass-range. These models are publicly available and may be used to analyse data coming from present and forthcoming
asteroseismic and spectroscopic surveys such as Gaia, TESS and PLATO
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Disappearance of the extended main sequence turn-off in intermediate age clusters as a consequence of magnetic braking
Author(s): Georgy C., Charbonnel C., Amard L., Bastian N., Ekström S., Lardo C., Palacios A., Eggenberger P., Cabrera-Ziri I., Gallet F., Lagarde N.
(Article) Published:
Astronomy & Astrophysics, vol. 622 p.A66 (2019)
Links openAccess full text :
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Anisotropic turbulent transport in stably stratified rotating stellar radiation zones
Author(s): Mathis S., Prat V., Amard L., Charbonnel C., Palacios A., Lagarde N., Eggenberger P.
(Article) Published:
Astronomy & Astrophysics, vol. 620 p.A22 (2018)
Links openAccess full text :
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