Simulations of turbulent convection in rotating young solar-like stars: Differential rotation and meridional circulation

We present the results of three-dimensional simulations of the deep convective envelope of a young (10 Myr) one-solar-mass star, obtained with the Anelastic Spherical Harmonic code. Since young stars are known to be faster rotators than their main sequence counterparts, we have systematically studied the impact of the stellar rotation speed, by considering stars spinning up to five times as fast as the Sun. The aim of these nonlinear models is to understand the complex interactions between convection and rotation. We discuss the influence of the turbulence level and of the rotation rate on the intensity and the topology of the mean flows. For all of the computed models, we find a solar-type superficial differential rotation, with an equatorial acceleration, and meridional circulation that exhibits a multicellular structure. Even if the differential rotation contrast decreases only marginally for high rotation rates, the meridional circulation intensity clearly weakens according to our simulations. We have also shown that, for Taylor numbers above a certain threshold (Ta>10^9), the convection can develop a vacillating behavior. Since simulations with high turbulence levels and rotation rates exhibit strongly cylindrical internal rotation profiles, we have considered the influence of baroclinic effects at the base of the convective envelope of these young Suns, to see whether such effect can modify the otherwise near cylindrical profiles to produce more conical, solar-like profiles.Comment: 32 pages, 18 figures, 2 tables, to appear in Ap

A la recherche des modes de gravité (étude de la dynamique du cœur solaire)

Cette thèse traite de l'étude de la dynamique de la zone radiative du Soleil. Le profil de rotation dans la partie centrale du Soleil est encore mal connu alors que le coeur représente plus de 50% de la masse solaire. Pour une vision globale de l'évolution des étoiles, nous voulons mettre des contraintes sur les processus dynamiques ayant lieu dans le Soleil. Nous avons emprunté plusieurs voies pour cette étude: la modélisation, la mise au point et l'étude d'un nouvel instrument, les observations et les inversions de la rotation. Une meilleure compréhension de la dynamique solaire nécessite la détection des modes de gravité. Pour cela, un prototype technologique construit au CEA (GOLF-NG) a pour but de valider des points techniques et de préparer une mission scientifique. Nous avons étudié le photodétecteur et l'instrument complet. Nous montrons sa faisabilité ainsi que son bon fonctionnement en observant la résonance des différents canaux. En attendant que cette mission prenne jour, l'analyse des données de GOLF, à bord de SoHO, nous a permis de détecter un candidat mode de gravité et d'observer la signature des modes de gravité dipolaires. Ce travail a en particulier bénéficié d'une approche théorique sur les fréquences de ces modes. Nous montrons l'impact de différents processus et quantités physiques sur ces prédictions. Enfin, les processus dynamiques au sein du Soleil étant mal contraints, nous avons étudié l'impact de l'ajout d'un ou plusieurs modes de gravité dans les inversions sur les profils de rotation extraits. Enfin, nous donnons des contraintes sur les observations afin d'obtenir une information non négligeable sur le profil de rotation dans le cœur.This thesis is dedicated to the study of the dynamics of the solar radiative zone through gravity modes. Though the core represents more than 50% of the solar mass, we still do not have an accurate vision of the rotation profile in the very inner part of the Sun. To understand the evolution of stars, we try to put constraints on dynamic processes. Several paths have been followed in this thesis to tackle this issue: solar modeling, the study of a new instrument, observations and inversions of the rotation. The necessity of the detection of gravity modes is driven by the will for a better comprehension of the solar dynamics. With a technological prototype built at the CEA (GOLF-NG), we want to validate a few technical points and prepare the scientific mission which aim will be to detect these gravity modes. We studied first the photodetector and then the whole instrument response. We show the feasibility of the instrument. The observation of the resonance in all the channels proves that it works the way we expected. However, before this mission takes place, the analysis of GOLF data enabled us to detect one gravity-mode candidate as well as the signature of dipole gravity modes. This work benefited from a more theoretical approach on the prediction of gravity-mode frequencies. We show the influence of several physical processes and quantities. Finally, as the dynamical processes in the Sun are not well constrained, we tried to understand the impact of the introduction of one and several gravity modes on the inferred rotation profiles. We also tried to give constraints on the observations so that we could obtain some information on the rotation profile in the core.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Rôle de l'héliosismologie dans la dynamique interne du Soleil et dans le problème des neutrinos solaires

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Structure et dynamique des étoiles de type solaire (de l'héliosismologie à l'astérosismologie)

CETTE THESE TRAITE DE LA SISMOLOGIE DES ETOILES ET DES CONTRAINTES QUE L ON PEUT ATTENDRE DES FUTURES MISSIONS SPATIALES (COROT, EDDINGTON ) SUR LA DYNAMIQUE INTERNE DES ETOILES DE TYPE SOLAIRE. CETTE ETUDE EST COMPLETEE PAR UN TRAVAIL DE SIMULATION NUMERIQUE 3D DE LA CONVECTION DANS UNE ETOILE JEUNE ET DES EFFETS DE LA ROTATION SUR CELLE-CI. LE BUT DE CE TRAVAIL EST DE DEPASSER LA VISION QUASI-STATIQUE DES ETOILES, QUI A PERMIS DE CERNER LES GRANDS PRINCIPES DE LA VIE DES ETOILES, MAIS NOUS A EGALEMENT MONTRE SES LIMITATIONS, EN PARTICULIER POUR LES ETOILES JEUNES A TRAVERS PAR EXEMPLE LE PROBLEME DU LITHIUM.AUJOURD HUI, LA CONVECTION DANS LES ETOILES EST TRAITEE DE FAÇON PHENOMENOLOGIQUE A L AIDE D UN SEUL PARAMETRE, ESTIME SUR LE SOLEIL. NOUS MONTRONS COMMENT MIEUX DETERMINER L ETENDUE DE LA CONVECTION AVEC UNE PRECISION DE 3 5% GRACE AUX PROCHAINES OBSERVATIONS COROT, EN TENANT COMPTE DES PROPRIETES DES MODES ACOUSTIQUES : EXCITATION STOCHASTIQUE, EFFET DE L ACTIVITE STELLAIRE L'INFORMATION SUR LA ROTATION EST CONTENUE DANS LE SPLITTING DES MODES, DISTANCE SEPARANT LES COMPOSANTES D'UN MEME MULTIPLET. NOUS MONTRONS COMMENT EXTRAIRE LE TAUX DE ROTATION ET L ORIENTATION DE L AXE DE ROTATION D UNE ETOILE TOURNANT AU MOINS DEUX FOIS PLUS VITE QUE LE SOLEIL. EN DEÇA, LES EFFETS DE CES DEUX INCONNUES SONT PLUS DIFFICILEMENT DISCERNABLES. NOUS AVONS SIMULE LES MOUVEMENTS DE CONVECTION DANS UN SOLEIL JEUNE TOURNANT JUSQU A CINQ FOIS PLUS VITE QUE LE SOLEIL. NOUS AVONS ETUDIE SON INTERMITTENCE, AINSI QUE LA REDISTRIBUTION DU MOMENT CINETIQUE ET LA MISE EN PLACE DE LA ROTATION DIFFERENTIELLE ET DE LA CIRCULATION MERIDIENNE EN FONCTION DU TAUX DE ROTATION.THIS THESIS DEALS WITH THE SEISMOLOGY OF STARS. WE DISCUSS THE CONSTRAINTS WHICH CAN BE OBTAINED WITH THE FUTURE SPACE MISSIONS (COROT, EDDINGTON...) ON THE INTERNAL DYNAMICS OF SOLAR-LIKE STARS. THIS STUDY IS COMPLETED BY A WORK ON 3D NUMERICAL SIMULATION OF CONVECTION IN A YOUNG STAR AND THE EFFECTS OF ROTATION ON THIS ONE. THE AIM OF THIS WORK IS TO EXCEED THE QUASI-STATIC VISION OF THE STARS. THIS VISION ENABLED US TO DETERMINE THE GREAT PRINCIPLES OF STELLAR EVOLUTION, BUT HAS ALSO SHOWED US ITS LIMITATIONS, IN PARTICULAR FOR YOUNG STARS, FOR EXAMPLE WITH THE PROBLEM OF LITHIUM.NOWADAYS THE CONVECTION IN STARS IS TREATED IN A PHENOMENOLOGICAL WAY USING ONLY ONE PARAMETER, ESTIMATED ON THE SUN. WE SHOW HOW TO DETERMINE THE EXTENT OF THE CONVECTION WITH AN ACCURACY OF 3 5% WITH THE NEXT COROT OBSERVATIONS. WE HAVE TAKEN INTO ACCOUNT THE PROPERTIES OF THE ACOUSTIC MODES: STOCHASTIC EXCITATION, EFFECT OF THE STELLAR ACTIVITY INFORMATION ON STELLAR ROTATION IS CONTAINED IN THE SPLITTING OF MODES, DISTANCE SEPARATING THE COMPONENTS OF A MULTIPLET. WE SHOW HOW TO EXTRACT THE ROTATION RATE AND THE ORIENTATION OF THE ROTATION AXIS OF A STAR SPINNING AT LEAST TWICE FASTER THAN THE SUN. FOR LESS SLOWLY ROTATING STARS, THE EFFECTS OF THESE TWO UNKNOWN FACTORS ARE DISCERNIBLE WITH MORE DIFFICULTY. WE SIMULATED THE MOVEMENTS OF CONVECTION IN A YOUNG SUN SPINNING UP TO FIVE TIMES MORE QUICKLY THAN THE SUN. WE STUDIED HIS INTERMITTENCY, THE REDISTRIBUTION OF THE KINETIC MOMENT AND THE INSTALLATION OF DIFFERENTIAL ROTATION AND MERIDIAN CIRCULATION, ACCORDING TO THE ROTATION RATE.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Evolution des étoiles jeunes de type solaire (apports du lithium et de la sismologie)

PARIS7-Bibliothèque centrale (751132105) / SudocMEUDON-Observatoire (920482302) / SudocSudocFranceF

Opacities in the massive stellar envelopes

Helio and asteroseismology (SoHo, CoRoT, KEPLER...) have produced observed acoustic oscillations of thousands of stars. The characteristics of these oscillations are deeply linked to the transport of radiation inside the stars. However, the comparisons of seismic data of Sun and stars with model predictions have led to significant discrepancies, which could be due to a bad knowledge of production and transport of energy.We will focus here on the case of β-Cephei.β-Cephei are pulsating stars, progenitor of supernovae and thus deeply linked to our understanding of stellar medium enrichment. Their study has shown some difficulty to predict the observed oscillation modes, which are directly linked to a bump of the opacity of the elements of the iron group (Cr, Fe, Ni) at log T=5.25 through their pulsating mechanism called the κ-mechanism. We will show that the different parameters of the stars (mass, age, metallicity) have a great influence on the amplitude of the bump, and then on the structure of the considered star.The mastery of the κ-mechanism that produces the pulsation of these stars supposes a fine determination of the peak opacity of the iron group in their envelope. We will present the final results of an experiment conducted at LULI 2000 in 2011 on Cr, Fe and Ni and compare them to OP and ATOMIC, SCO-RCG codes. We will show how to improve the opacity in the range of temperature around log T= 5.3

The dynamics of the radiative zone of the Sun

International audienceHelioseismology puts strong constraints on the internal sound speed and on the rotation profile in the radiative zone. Young stars of solar type are more active and faster rotators than the Sun. So we begin to build models which include different rotation histories and compare the results with all the solar observations. The profiles of the rotation we get have interesting consequence for the introduction of magnetic field in the radiative zone. We discuss also the impact of mass loss deduced from measured flux of young stars. We deduce from these comparisons some quantitative effect of the dynamical processes (rotation, magnetic field and mass loss) of these early stages on the present sound speed and density. We show finally how we can improve our present knowledge of the radiative zone with PICARD and GOLFNG