Surprising Sun: A New Step Towards a Complete Picture?

Turck‐Chièze, S.; Couvidat, S.; Piau, L.; Ferguson, Jason W.; Lambert, Pascal; Ballot, J.; García, R. A.; Nghiem, P.

doi:10.1103/physrevlett.93.211102

Cited by 165 publications

(146 citation statements)

References 30 publications

(33 reference statements)

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“…They are as reliable as the solar models. The dynamics of the Sun radiation zone is largely uncertain as suggested by helioseismology (Turck-Chièze et al 2004). It probably involves angular momentum transport through internal waves (Charbonnel & Talon 2005;Mathis et al 2008).…”

Section: Convection Length Scales From the Sunmentioning

confidence: 99%

Surface convection and red-giant radius measurements

Piau

Kervella

Dib

et al. 2011

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Phenomenological models of convection adopt characteristic length scales that are chosen to fit solar or stellar observations. We investigate whether changes in these length scales are required between the Sun and low mass stars on the red giant branch (RGB). The question is addressed jointly in the frameworks of the mixing length theory and the full spectrum of turbulence model. For both models, the convective length scale is assumed to be a fixed fraction of the local pressure scale height. We use constraints provided by the observed effective temperatures and linear radii independently. We consider a sample of 38 nearby giants and subgiants for which surface temperatures and luminosities are known accurately and the radii are determined by interferometry to better than 10%. We computed dedicated models for the few cases where the stellar masses were determined by asteroseismological measurements. First we calibrated the solar models. With the same physics, we then computed RGB models for masses between 0.9 M and 2.5 M and metallicities ranging from [Fe/H] = −0.34 to solar. The evolution is followed up to 10 3 L . Special attention is given to the opacities and the non-grey atmosphere models used as boundary conditions for which the model of convection is the same as in the interior. For both the mixing length theory and the full spectrum of turbulence models, the characteristic solar length scale for convection has to be slightly reduced to fit the lower edge of the observed RGB. The corresponding models also agree more closely with the expected mass distribution on the RGB and the seismic constraints. These results are robust regardless of effective temperatures determined spectroscopically or radii determined interferometrically are used.

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Section: Convection Length Scales From the Sunmentioning

confidence: 99%

Surface convection and red-giant radius measurements

Piau

Kervella

Dib

et al. 2011

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“…We consider that the initial composition is the initial composition of our calibrated solar models including diffusion i.e. X = 0.7195 and Y = 0.2664 (Turck-Chièze et al 2004). Because diffusion takes the metals away from the surface, the diffusive models for a given mass and Z/X surface ratio are cooler than the non diffusive models with the same Z/X surface ratio.…”

Section: Diffusion Effectsmentioning

confidence: 99%

Impact of the physical processes in the modeling of HD 49933

Piau¹,

Turck‐Chièze²,

Duez³

et al. 2009

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Context. On its asteroseismic side, the initial run of CoRoT was partly devoted to the solar like star HD 49933. The eigenmodes of this F dwarf have been observed with unprecedented accuracy. Aims. We investigate quantitatively the impact of changes in the modeling parameters like mass and composition. More importantly we investigate how a sophisticated physics affects the seismological picture of HD 49933. We consider the effects of diffusion, rotation and the changes in convection efficiency. Methods. We use the CESAM stellar evolution code coupled to the ADIPLS adiabatic pulsation package to build secular models and their associated oscillation frequencies. We also exploited the hydrodynamical code STAGGER to perform surface convection calculations. The seismic variables used in this work are: the large frequency separation, the derivative of the surface phase shift, and the eigenfrequencies ν =0,n=14 and ν =0,n=27 . Results. Mass and uncertainties on the composition have much larger impacts on the seismic variables we consider than the rotation. The derivative of the surface phase shift is a promising variable for the determination of the helium content. The seismological variables of HD 49933 are sensitive to the assumed solar composition and also to the presence of diffusion in the models.

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“…The young Sun model used as a reference is a Cesam nonrotating standard one (Morel 1997), following input from the work of Couvidat et al (2003) and Turck-Chièze et al (2004). In Fig.…”

Section: Fossil Fields Buried In Late-type Stars Radiative Coresmentioning

confidence: 99%

Relaxed equilibrium configurations to model fossil fields

Duez

Mathis

2010

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Context. The understanding of fossil fields' origin, topology, and stability is one of the corner stones of the stellar magnetism theory. On one hand, since they survive on secular time scales, they may modify the structure and the evolution of their host stars. On the other hand, they must have a complex stable structure since it has been demonstrated that the simplest purely poloidal or toroidal fields are unstable on dynamical time scales. In this context, the only stable configuration found today is the one resulting from a numerical simulation by Braithwaite and collaborators who studied the evolution of an initial stochastic magnetic field, which is found to relax on a mixed stable configuration (poloidal and toroidal) that seems to be in equilibrium and then diffuses. Aims. We investigate an equilibrium field in a semi-analytical way. In this first article, we study the barotropic magnetohydrostatic equilibrium states. Methods. The problem reduces to a Grad-Shafranov-like equation with arbitrary functions. These functions are constrained by deriving the lowest-energy equilibrium states for given invariants of the considered axisymmetric problem, in particular for a given helicity known to be one of the causes of such problems. These theoretical results were applied to realistic stellar cases, the solar radiative core and the envelope of an Ap star, and discussed. In both cases we assumed that the field is initially confined in the stellar radiation zone.Results. The generalization of the force-free Taylor's relaxation states studied in laboratory experiments (in spheromaks) that become non force-free in the self-gravitating stellar case are obtained. The case of general baroclinic equilibrium states will be studied in Paper II.

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Surprising Sun: A New Step Towards a Complete Picture?

Cited by 165 publications

References 30 publications

Surface convection and red-giant radius measurements

Surface convection and red-giant radius measurements

Impact of the physical processes in the modeling of HD 49933

Relaxed equilibrium configurations to model fossil fields

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