WorldCat Identities

Laboratoire Joseph-Louis Lagrange (Nice, Alpes-Maritimes)

Overview
Works: 58 works in 60 publications in 2 languages and 60 library holdings
Roles: Other
Publication Timeline
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Most widely held works by Alpes-Maritimes) Laboratoire Joseph-Louis Lagrange (Nice
Étude du disque galactique par marquage chimique de ses populations stellaires by Guillaume Guiglion( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Studying both the chemical composition and kinematics of Milky Way stars is essential to understand how big structures of our Galaxy are formed. Indeed, low-mass stars retain in their photosphere the chemical composition of the interstellar medium is which they were born. Additionally, the kinematics are essential to characterize stellar populations. In this thesis, we focus on the galactic disc, a major component of the Milky Way. In the context of the Gaia mission, we have developed an automatic procedure GAUGUIN, devoted to deriving chemical abundances. We first applied our method to the Gaia-ESO Survey (GES) data to derive alpha and iron-peak chemical abundances for 10000 stars. We then derived lithium abundances for 7300 stars from the AMBRE project. GAUGUIN is well adapted to massive spectroscopic surveys, both in terms of computation time and accuracy. GAUGUIN will be soon integrated into the RVS DPAC analysis pipeline of the Gaia mission. We studied the velocity dispersions in the galactic disc as a function of the [Mg/Fe] ratio, used as an age proxy. Thanks to 6800 GES stars, we detected thick disc stars with cool kinematics and high [Mg/Fe] ratio, so presumably old. In the generally turbulent context of the primitive galactic disc, this thesis places these results in the framework of the different disc formation and evolution scenarios. We also showed that the lithium abundance in the galactic disc increases as a function of the metallicity in the domain -1<[M/H]+0 dex and decreases at super-solar metallicities. Finally, the thin and the thick discs could be characterized by different lithium abundance evolutions
Classification morphologique d'un échantillon optique d'amas de galaxies by Florent Rostagni( Book )

2 editions published in 2014 in French and held by 2 WorldCat member libraries worldwide

Clusters of galaxies are one of the main cosmological probes used to constrain the cosmological parameters, through their mass function and their growth rate. The measure of these two quantities require the determination of the dynamical state of clusters. The present and future large and deep sky surveys give access to a more complete information on clusters and legitimate the development of new methods of determination of their dynamical state. In this thesis, a new method of characterization of the cluster morphology has been developed. It is a 2+1D method using galaxies and it enables to develop a new morphological classification of clusters. Structures around clusters are detected and characterized in projection and along the line of sight using a wavelet analysis. The new classification consists in counting the number of structures in the vicinity of clusters, three clusters classes were defined : unimodal, bimodal and multimodal. The ellipticity and the Gaussianity of the distribution of radial velocities are also used to refine the classification. The method was applied to a subsample of 403 clusters from the C4cluster catalogue using data from the SDSS. The results are : 25% of the clusters are unimodals, 33% are bimodals and 42% are multimodals. The stability of the classification with respect to the different parameters used was also performed as well as a comparison with the results from other studies in the literature
Imagerie optique à très haut contraste : une approche instrumentale optimale by Mathilde Beaulieu( )

1 edition published in 2017 in French and held by 1 WorldCat member library worldwide

Cette thèse vise à investiguer des moyens d'optimiser les performances de l'imagerie à haut contraste dans l'optique et le proche infrarouge pour la détection d'exo-planètes. L'étude principale a été menée sur le contraste à faible séparation permettant l'imagerie d'exo-planètes dans leur zone habitable. Cette détection directe est rendue possible par le développement des futurs grands télescopes et de coronographes de plus en plus performants à faible séparation. L'approche retenue permet de créer une zone sombre à haut contraste grâce à la coronographie et au « wavefront shaping » (contrôle de l'amplitude et de la phase avec 2 miroirs déformables), mais qui est limité par les effets de propagation de Fresnel. Les résultats obtenus ont déterminé les limitations de configuration optique pour le « wavefront shaping ». Grâce à une approche semi-analytique soutenue par des simulations numériques et une approche Monte-Carlo, ces limitations ont été analysées et quantifiées pour extraire les configurations optimales. Les résultats ont été appliqués au banc SPEED dont l'objectif est d'optimiser et de tester le haut contraste à faible séparation. Une deuxième étude a été une contribution à une étude générale de stabilité, en traitant la stabilité temporelle comme un paramètre indispensable dans la conception en amont d'instrument haut contraste. Un travail préliminaire a été initié sur la stabilité des instruments de mesure eux-mêmes à travers l'étude thermique d'un système de métrologie. Enfin, un dernier volet a été une étude de simulation de performances d'un nouveau concept d'imagerie différentielle basé sur l'acquisition d'images réalisées avec différentes tailles de pupilles
Kernel LMS à noyau gaussien : conception, analyse et applications à divers contextes by Wei Gao( )

1 edition published in 2015 in English and held by 1 WorldCat member library worldwide

The main objective of this thesis is to derive and analyze the Gaussian kernel least-mean-square (LMS) algorithm within three frameworks involving single and multiple kernels, real-valued and complex-valued, non-cooperative and cooperative distributed learning over networks. This work focuses on the stochastic behavior analysis of these kernel LMS algorithms in the mean and mean-square error sense. All the analyses are validated by numerical simulations. First, we review the basic LMS algorithm, reproducing kernel Hilbert space (RKHS), framework and state-of-the-art kernel adaptive filtering algorithms. Then, we study the convergence behavior of the Gaussian kernel LMS in the case where the statistics of the elements of the so-called dictionary only partially match the statistics of the input data. We introduced a modified kernel LMS algorithm based on forward-backward splitting to deal with ℓ₁-norm regularization. The stability of the proposed algorithm is then discussed. After a review of two families of multikernel LMS algorithms, we focus on the convergence behavior of the multiple-input multikernel LMS algorithm. More generally, the characteristics of multikernel LMS algorithms are analyzed theoretically and confirmed by simulation results. Next, the augmented complex kernel LMS algorithm is introduced based on the framework of complex multikernel adaptive filtering. Then, we analyze the convergence behavior of algorithm in the mean-square error sense. Finally, in order to cope with the distributed estimation problems over networks, we derive functional diffusion strategies in RKHS. The stability of the algorithm in the mean sense is analyzed
Observations et modélisations spectro-interférométriques longue base des étoiles et de leur environnement proche by Macinissa Hadjara( )

1 edition published in 2015 in French and held by 1 WorldCat member library worldwide

Cette thèse présente les résultats d'observations d'étoiles en rotation rapide menées sur le spectro-interféromètre AMBER du VLTI dans ses modes haute et moyenne résolutions spectrales. Les mesures effectuées sont les visibilités estimées sur trois bases simultanées, les phases différentielles en fonction de la longueur d'onde et des phases de clôtures avec, pour certaines nuits une bonne couverture du plan (u,v). Les données utilisées sont issues de plusieurs campagnes d'observation. Ces dernières étaient fortement dégradées par les défauts optiques d'AMBER, et affectés par des bruits classiques d'interférométrie optique à longue base en IR: défauts du détecteur, bruit de lecture, instabilités du suiveur de franges, ...etc. Leur analyse a nécessité la mise au point d'outils numériques de réduction spécifiques pour atteindre les précisions nécessaires à l'interprétation de mesures interférométriques. Pour interpréter ces mesures j'ai développé un modèle semi-analytique chromatique d'étoile en rotation rapide qui m'a permis d'estimer, à partir des phases différentielles; le degré d'aplatissement, le rayon équatorial, la vitesse de rotation, l'angle d'inclinaison, l'angle position de l'axe de rotation de l'étoile sur le ciel, la distribution de la température effective locale et de la gravité à la surface de l'étoile dans le cadre du théorème de von Zeipel. Les résultats concernant 4 étoiles massives de types spectraux B, A et F m'ont permis de les caractériser pour les mécanismes évoqués ci-dessus et d'ouvrir ainsi la perspective d'études plus systématiques d'objets similaires en étendant ultérieurement ces études à la relation photosphère-enveloppe circumstellaire
Étude de l'atmosphère de Vénus à l'aide d'un modèle de réfraction lors du passage devant le Soleil des 5-6 Juin 2012 by Christophe Pere( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

The transit of Venus across the Sun is a rare and unique opportunity to study therefraction of sunlight through the atmosphere, called the "aureola", and determine the atmosphericproperties of the planet and in particular the thermal structure of the upper atmosphere. Theobjective of this thesis was the modeling of this refraction effect at terminator during the passageacross the Sun which took place on June, 5-6 2012, and a comparison with data obtained in thesame region during the Venus Express mission.The first part is devoted to the analysis of data from an Earth-orbiting solar observatory thatallowed the creation of individual aureola light curves according to latitude, that were used as amodeling reference. The study of the refracting atmosphere was first carried out by an isothermalapproach (Baum and Code (1953) theory). The model was then refined by simulating threeconcentric layers based on prior analysis of Venus Express/SPICAV-SOIR vertical density profiledata obtained simultaneously on June 6, 2012. Finally, the complete model developed for thisstudy is a concentric layered model with sub-kilometer vertical resolution. This model has allowedus to retrieve from individual aureole lightcurves a density vertical profile function of the latitudeand the tau = 1 altitude of slanted opacity along the line of sight, induced by mesospheric aerosols.These data were subsequently used to generate temperature maps in 2D function of latitude andaltitude, we compare the solar occultation data from the Venus Express mission (SOIR). This studyalso determined independently the scale height of aerosols and the chromaticity in the atmosphereof Venus.A separate, additional study on 2004 Venus transit data was conducted jointly with Dr.Andrea Chiavassa to highlight the impact of the stellar granulation on exoplanetary transit curves inextrasolar systems
L'enveloppe circumstellaire des Céphéides et l'étalonnage des distances dans l'Univers by Vincent Hocdé( )

1 edition published in 2020 in French and held by 1 WorldCat member library worldwide

Les Céphéides occupent une place centrale dans l'étalonnage des distances dans l'Univers. Cependant ces étoiles semblent présenter un excès infrarouge qui pourrait prendre son origine dans leur enveloppe circumstellaire, et ainsi entraîner des biais photométriques dans le calcul des distances. Or la nature et l'origine de ces enveloppes, de même que les mécanismes physiques responsables de l'excès infrarouge demeurent inconnus. La thèse a pour objectif de déterminer les mécanismes physiques à l'origine de l'excès infrarouge des Céphéides provenant de leur enveloppe circumstellaire, et d'évaluer ses effets sur l'étalonnage des distances dans l'Univers. Dans une première partie je reconstruis l'excès infrarouge de 5 Céphéides Galactiques en comparant des observations spectroscopiques du télescope spatial Spitzer avec le modèle de photosphère de ces Céphéides au cours du cycle de pulsation. Je montre que la plus grande partie de l'excès infrarouge ne peut-être expliquée par une enveloppe de poussière. Je considère ensuite un modèle analytique de coquille de gaz d'hydrogène ionisé. L'ajustement des paramètres physiques de ce modèle me permet de reproduire l'excès infrarouge de manière satisfaisante. En particulier, je détermine des enveloppes dont le rayon est d'environ 1.15 Rstar c'est à dire dans une région qui pourrait être assimilée à la basse chromosphère des Céphéides. Pour mieux comprendre l'origine du gaz ionisé, j'étudie ensuite les profils à haute résolution spectrale des raies de Halpha et du triplet du calcium obtenus par le spectroscope UVES au VLTI, à partir d'un échantillon de 24 Céphéides, au cours du cycle de pulsation. Je montre que la chromosphère est activée à chaque cycle par la propagation du choc supersonique principal, qui chauffe et ionise le gaz de l'atmosphère. La retombée balistique des plus hautes couches peut aussi accélérer jusqu'à atteindre une vitesse supersonique et ioniser le gaz. Dans le cas des Céphéides de longues périodes, la dé-synchronisation entre la propagation du choc et la retombée de l'atmosphère provoque un profil en double absorption qui me permet d'estimer le rayon de la chromosphère à 1.5Rstar En outre, des raies d'absorption de Halpha centrées sur le référentiel de l'étoile suggèrent l'existence d'enveloppes de gaz à au moins 2 Rstar. Enfin, grâce aux observations interférométriques que j'ai réalisées à l'aide de l'instrument MATISSE/VLTI dans le cadre du consortium, j'apporte de nouvelles contraintes dans les bandes infrarouges L, M et N en étudiant la Céphéide l Car. Je montre pour la première fois l'existence d'un environnement centro-symétrique résolu en bande L, dont le rayon est d'environ 1.9 Rstar, en accord avec de précédentes observations interférométriques en bande K. De plus, l'analyse des spectres obtenus montre de manière significative l'absence de signature de poussière, renforçant une nouvelle fois l'hypothèse d'une enveloppe gazeuse. Cependant, le modèle de coquille de gaz ionisé ne peut pas reproduire en même temps l'excès IR et la taille déterminée par MATISSE (1.15 Rstar versus 1.9 Rstar). Une perspective théorique d'amélioration du modèle consiste à étudier l'hydrogène négatif comme source d'opacité du gaz. De nouvelles observations à venir avec l'instrument MATISSE permettront d'étudier les propriétés des enveloppes en fonction de la position des Céphéides dans le diagramme HR. L'objectif de ces observations est de permettre d'établir une grille de corrections photométriques à appliquer lors de la détermination de la distance des Céphéides
Correction active des discontinuités pupillaires des télescopes à miroir segmenté pour l'imagerie haut contraste et la haute résolution angulaire by Pierre Janin-Potiron( )

1 edition published in 2017 in French and held by 1 WorldCat member library worldwide

Searching for extraterrestrial life through the observation and characterization of exoplanets is, amongst others, one of the major goal of the modern astrophysics. This quest translate from an instrumental point of view to the development of telescope capable of reaching higher angular resolution that what is actually ongoing. That is why the future projects of extremely large telescopes are using primary mirrors exceeding the 30 meters in diameter. Their conception is consequently based, for technical and technological reasons, on a segmented geometry. The segmentation of the primary mirror therefore implies a growing complexity of the structure of its pupil. In order to reach the optical quality required by the sciences cases of interest, taking into account and correct for the effects introduced by a poor alignment of the segments is mandatory, as the angular resolution of a non-cophased telescope is equivalent to the one obtained with a single segment. In this context, I develop in this manuscript two cophasing sensors allowing to measure and correct for the aberrations of piston, tip and tilt present on a segmented pupil. The first one, the Self-Coherent Camera - Phasing Sensor (SCC-PS), is based on a focal plane analysis of the signal. The second one, the ZELDA - Phasing Sensor (ZELDA-PS), is based on a pupil plane analysis of the signal. The results obtained by means of numerical simulations and the first results coming from the implementation of the SCC-PS on an optical bench are presented in this manuscript
Simulations numériques de disques protoplanétaires : prédictions théoriques pour interprétation observationnelle by Clément Robert( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

To this day, thousands of planets have been identified outside of our own solar system. Theirformation is thus not an unlikely occurence. A number of still-forming young stars are also known,circled by remnants of gas and dust which are shaped by centrifugal forces into disk-like objects. Inthose disks, planets are born as they accumulate nearby material. Although the successive steps of thisevolution, from micrometric grains to planet-sized objects are relatively well identified, the remainingchallenges are numerous. Indeed, small size solids tend to rapidly accrete (in a few million years) ontothe star. It is also the case (albeit for different reasons) of planet-mass objects, which concede theirangular momentum to the circumstellar disk. In this thesis, I study possible solutions to such problemsthrough hydrodynamical simulations. I show that, contrary to a received idea, migration of giantplanets does not follow the viscous spreading in the disk. Moreover, I highlight that planetary accretiondoes not significantly affect migration rates. Then, I deal with a scenario that favours constructiveagregation of dust, namely Rossby vortices, whose existence is still debated for we lack observationalconstraints. I show that such structures could be identified through a handful of observables, amongwhich dynamical signatures seen in Doppler shifts. Using radiative transfer as a post-processing meth-od,I provide additional predictions for signatures in interferometric observations of thermal emission, aswell as polarimetric features of those vortices. Finally, I dedicate my last chapter to describing my maincontributions to open source projects that I used throughout my thesis
Mesures optiques de profils de turbulence pour les futurs systèmes d'optique adaptative et d'observation by Khanh Linh Nguyen( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

The knowledge of atmospheric turbulence in horizontal aim allows to better understand the physics of the heat fluxes at the ground-atmosphere interface. It also allows, in vertical aim, to improve the performance of future wide-field adaptive optics systems for astronomical observation. The profile of Cn²locally characterizes the force of turbulence. The CO-SLIDAR method, developed by ONERA, allows profiles of Cn² along the line of sight of the telescope, from the slopes and scintillations of a double source measured by Shack-Hartmann analyzer. This method was validated in vertical aim but had not yet shown its effectiveness in horizontal aim. The two experiments in Lannemezan and Châtillon-Meudon introduced a new Shack-Hartmann Infrared profilometer: the SCINDAR. They were carried out on heterogeneous and piecewise homogeneous surfaces respectively, and they participate in the validation of the method for agronomic and ecological applications. My study consists of improving SCINDAR profilometer signal processing and validating the CO-SLIDAR method for near-ground atmospheric turbulence measurements. This method has been adapted using a spherical wave propagation formalism. The study identified and took into account sources of error in processing: the cold machine vibration of the SCINDAR cryogenic wavefront analyzer and the extent of the sources in the weight functions of the direct model set for data processing. My study focuses on improvement of the SCINDAR data processing and experimental validation profiles Cn² obtained with Cn² measurements acquired by scintillometers. I first built a database of slopes and scintillations of verified quality. For the inversion of the data, I chose the L1L2 regularization which is suitable for near-ground Cn² measurements. The method of setting the hyperparameters of this regularization is unsupervised. It makes it possible to increase the reliability and the accuracy of the Cn² profile estimation in a pragmatic way using the relative errors of the macroscopic turbulent parameters. The SCINDAR profilometer with the improved CO-SLIDAR method finally produces Cn² profiles of excellent quality. These profiles are successfully compared to scintillometer measurements. All of this work constitues the adaptation of the CO-SLIDAR method for measurements of near-ground turbulence
Étude de la pulsation des étoiles de type RR Lyrae et de l'effet Blazhko by Cyrus Zalian-Rahatabad( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

In this thesis we develop a new theory of the Blazhko effect. We also provide a theoretical justification to the following commonly observed facts: the light curve harmonics decrease; the asymetry of envelopes and sidelobes ; the synchronization of layers and the mode selection. The first part of this thesis is dedicated to the extensive study of a RR Lyrae star presenting the Blazhko effect: S Arae. Firstly, a rigorous definition of harmonic analysis applied to light curves is given. This work, which has never been undertaken in the asteroseismology field, up to now, allows a better interpretation of the usual results of photometric studies. We carry on with the presentation of a software that we have developed, dedicated to frequency analysis: PDM13. After that, we perform the usual analysis of the frequency spectrum of the light curve, which we complete we two rigorous demonstrations of commonly observed facts: the harmonics decrease and the asymmetry induced by modulation. We complete it with a study of the parameters which vary during a Blazhko cycle, on which we will capitalize to understand this modulation effect. The second part begins with a reminder of the basic perturbed and linearized equations of stellar pulsation together with the oscillation mechanisms. We pursue this presentation with a non linear and discrete formalism that we have developed for these equations. This formalism will allow us to underline the importance of synchronization in those stars, but, most of all, it will lead us to a new theory of the Blazhko effect, based on solitons, which will be supported by a new results obtained with the wavelet transform method
Méthodes de détection parcimonieuses pour signaux faibles dans du bruit : application à des données hyperspectrales de type astrophysique by Silvia Paris( )

1 edition published in 2013 in English and held by 1 WorldCat member library worldwide

This thesis deals with the problem of detecting unknown signals at low Signal- to- Noise Ratio. This work focuses on the definition, study and implementation of efficient methods able to discern only-noise observations from those that presumably carry the information of interest in a sparse way. The relevance of these methods is assessed on hyperspectral data as an applicative part. In the first part of this work, the basic principles of statistical hypothesis testing together with a general overview on sparse representations, estimation and detection are introduced. In the second part of the manuscript, two statistical hypotheses tests are proposed and studied. Both are adapted to the detection of sparse signals. The behaviors and the relative differences between the tests are theoretically investigated through a detailed study of their analytical and structural characteristics. The tests' detection performances are compared with those of classical frequentist and Bayesian methods. According to the three-dimensional data sets considered in the applicative part, and to be closer to realistic scenarios involving data acquisition systems, the proposed detection strategies are then adapted in order to: i) account for spectrally variable noise; ii) exploit the spectral similarities of neighbors pixels in the spatial domain and iii) exploit the greater accuracy brought by dictionary-based models, which take into account the spatiospectral blur of information caused by instrumental Point Spread Functions. The tests are finally applied to massive astrophysical hyperspectral data in the context of the European Southern Observatory's Multi Unit Spectroscopic Explorer
Mise en œuvre et exploitation d'un spectromètre imageur pour l'étude sismique et la dynamique atmosphérique des planètes géantes by Didier Gonçalves( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

Connaitre précisément la structure interne des corps célestes est indispensable pour, à la fois, comprendre la physique qui régit leur existence et le processus qui leur a donné naissance. La sismologie, d'abord appliquée à la Terre puis au soleil, s'est révélée être un outil très efficace pour sonder leurs intérieurs. Dans les années 70 (Vorontsov et al 1976), des premiers travaux théoriques ont étudié la possibilité d'une sismologie des planètes géantes gazeuses. Les premières tentatives de mesures d'oscillations ont eu lieu à la fin des années 80. La détection des modes d'oscillations de Jupiter s'est avérée une entreprise très délicate en raison de sa rotation rapide. Pour augmenter les chances de détection, un instrument spécifique a été construit au début des années 2000 à l'OCA. Cet instrument, appelé SYMPA, est un spectromètre imageur de type Mach-Zehnder capable de produire une carte de vitesse radiale de Jupiter. Une détection de modes d'oscillations sur Jupiter par cet instrument a été publiée par Gaulme et al en 2011. Une version améliorée de l'instrument (appelé DSI) a été proposée pour la mission spatiale JUICE à destination de Jupiter, et un nouveau prototype a été construit dans ce but. Par la suite, le projet s'est réorienté vers un programme d'observation depuis le sol sous la forme d'un réseau de trois télescopes répartis en longitude (USA, France, Japon) et financé par l'ANR à partir de 2015 (ANR JOVIAL). L'intérêt de la mise en réseau est d'assurer la continuité des données (météo mise à part). L'instrument étant capable de produire des cartes de vitesse radiales, le projet permet également l'étude de la dynamique atmosphérique des planètes géantes. Ce travail de thèse s'inscrit dans le contexte de préparation de JOVIAL, avec pour objectif de caractériser l'instrument en laboratoire et d'identifier les problèmes liés aux conditions réelles d'observation. Les mesures en laboratoires ont montré des performances conformes aux attentes, avec un bruit de mesure propre à l'instrument inférieur au bruit de photon attendu sur Jupiter. Les premières mesures sur le ciel avec un télescope ont mis en évidence une sensibilité de l'instrument au degré de polarisation de la lumière ainsi qu'une dérive de la vitesse mesurée liée aux instabilités de position de la pupille pendant les observations. Le design de l'instrument et de son interface avec le télescope a été revu pour résoudre ces problèmes. Plusieurs campagnes d'observations de Jupiter ont été réalisées, permettant de mettre sur pied une chaine complète de traitement des données, dont la validité a été vérifiée par des simulations réalistes. Les observations de Jupiter ont donné des résultats scientifiques particulièrement intéressants. L'analyse des données de deux campagnes de 2015 et 2016 a fourni des séquences temporelles de cartes de vitesses radiales de Jupiter. Une première étude a consisté à chercher dans ces cartes la signature des vents zonaux et de les comparer aux mesures réalisées par suivi des nuages sur des images résolues (cloud-tracking). Une telle mesure n'avait jamais été faite par effet Doppler. Le résultat, bien qu'affecté par des biais de mesures identifiés, montre des profils de vents stables d'une année sur l'autre et en cohérence avec les valeurs issues du cloud-tracking, sauf au niveau de la partie nord de la bande équatoriale de Jupiter. La mesure Doppler suggère en effet une vitesse de vent bien inférieure à la vitesse apparente dans cette zone, ce qui a potentiellement des implications sur les modèles de dynamique atmosphérique. Ces résultats sont très importants pour mieux comprendre les mesures de la sonde Juno, actuellement en orbite autour de Jupiter. L'analyse fréquentielle des données temporelles a été abordée en fin de thèse. Les analyses préliminaires ne semblent pas pour l'instant reproduire la détection de SYMPA. Une analyse plus poussée est nécessaire avant de conclure à une absence du signal
Méthodes de démélange non-linéaires pour l'imagerie hyperspectrale by Hoàng Nguyên Nguyễn( )

1 edition published in 2013 in French and held by 1 WorldCat member library worldwide

In this thesis , we present several aspects of hyperspectral imaging technology , while focusing on the problem of non- linear unmixing . We have proposed three solutions for this task. The first one is integrating the advantages of manifold learning in classical unmixing methods to design their nonlinear versions . Results with data generated on a well-known manifold- the " Swissroll " - seem promising. The methods work much better with the increase in non- linearity compared with their linear version. However, the absence of constraint of non- negativity in these methods remains an open question for improvements . The second proposal is using the pre-image method for estimating an inverse transformation of the data form pixel space to abundance of space . The adoption of spatial information as " total variation " is also introduced to make the algorithm more robust to noise . However, the problem of obtaining ground truth data required for learning step limits the application of such algorithms
Méthodes numériques probabilistes : problèmes multi-échelles et problèmes de champs moyen by Camilo Andrés Garcia Trillos( )

1 edition published in 2013 in English and held by 1 WorldCat member library worldwide

This Ph.D. thesis deals with the numerical solution of two types of stochastic problems. First, we investigate the numeric solution to strongly oscillating SDEs, i.e. systems in which some ergodic state variables evolve quickly with respect to the remaining ones. We propose an algorithm that uses homogenization results and consists of an Euler scheme for the slow scale variables coupled with a decreasing step estimator for the ergodic averages of the fast variables. We prove the strong convergence of the algorithm as well as a generalized central limit theorem result for the normalized error distribution. In addition, we propose an extrapolated version applicable under stronger regularity assumptions and which satisfies the same properties of the original algorithm with lower asymptotic complexity. Then, we treat the problem of solving decoupled Forward Backward Stochastic Differential equations of McKean-Vlasov type (MKV-FBSDE) which appear in some stochastic control problems in an environment of a large number of particles with mean field interactions. As a first step, we propose a new algorithm, based on the cubature method on Wiener spaces, to weakly approach the solution of a McKean-Vlasov SDE. It is deterministic and can be parametrized to obtain any given order of convergence. Using this first forward approximation algorithm, we construct two procedures to solve the decoupled MKV-FBSDE and show that they converge with orders one and two under appropriate regularity conditions. Finally, we consider the problem of reducing the complexity of the presented method while preserving the presented convergence rates
Indicateurs chimiques d'âge stellaire à l'ère de Gaia by Anastasia Titarenko( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Stars record the past in their ages, chemical compositions and kinematics. They can provide unprecedented detailed constraints on the early epochs of galaxy formation, back to redshifts greater than two (a look-back time of around 10 billion years). In particular, stellar ages are crucial to the understanding of the Milky Way history and for comparison with galactic evolution models. The advent of the Gaia space mission has opened the path to stellar age estimations for large samples of stars, in particular, based on isochrone fitting methods. In addition, Gaia precise distances allow to develop indirect age estimations based on the stellar population chemical evolution clock. In fact, the chemical abundance patterns imprinted on stellar atmospheres represent the gas conditions at the time of the stars' formation back to redshifts greater than two. The chemical evolution products of different nucleosynthetic channels can therefore provide a time proxy. After calibration, it can be used as an age estimator.This thesis is focussed on the use of a particular chemical clock, the [Y/Mg] abundance. To this purpose, the astrometric Gaia mission data from the first data release was combined with high resolution spectroscopic data from the AMBRE-HARPS catalogue. First of all, the object identification of the AMBRE archival data was improved, thanks to a cross match with the 2MASS catalog, and later the Gaia DR1. In total, 6776 different stars have been identified.Secondly, in order to obtain precise estimations of the [Y/Mg] abundance ratio for galactic disc stars, the automated GAUGUIN tool integrated in the Gaia DPAC APSIS chain, has been optimized and tested. In particular, the abundance estimation capabilities of the APSIS GAUGUIN tool have been improved for irregularly distributed synthetic spectra grids, spanning a large range in stellar atmospheric parameters.Thirdly, the [Y/Mg] abundance ratio has been estimated for about 2000 stars from the AMBRE HARPS spectroscopic data. In addition, the internal and external errors of the abundances were carefully analysed. The studied stars belong mainly to the galactic thin and thick disc, in the metallicity range from --1.0 dex to 0.5 dex.Fourth, thanks to the isochrone fitting age estimations of 342 turn-off stars of the sample, the age sensitivity of the [Y/Mg] ratio has been studied. The analysis reveals a clear correlation between [Y/Mg] and age for thin disk stars of different metallicities, in synergy with previous studies of Solar type stars. In addition, no metallicity dependence with stellar age is detected, allowing to use the [Y/Mg] ratio as a reliable age proxy.Finally, the [Y/Mg] vs. age relation presents a discontinuity between thin and thick disk stars around 9-10 Gyrs. For thick disk stars, the correlation has a different zero point and probably a steeper trend with age, reflecting the different chemical evolution histories of the two disk components
Observables robustes pour la détection haut-contraste à faible séparation angulaire by Romain Laugier( )

1 edition published in 2020 in French and held by 1 WorldCat member library worldwide

The study of exoplanets has been a very active topic in the past years. Despite the indirect nature of most detections to date, those already provide us with a wealth of information on the properties of these exoplanetary systems, like their mass, size, and orbital elements. However, the direct detection of the light emitted or reflected by those planets provides some even more precious information. Coronagraphic instruments that would allow this are generally limited by the wavefront quality at their input, which prevents them from reaching their theoretical performance. Conversely, techniques employing observables designed to be robust to those aberrations are limited by photon noise. These two methods are made incompatible because coronagraphy breaks the convolution relationship betwen the object and its image. The works described in this thesis explore different avenues aiming to sidestep this incompatibility and to combine the performance of coronagraphic and interferometric methods though technology transfers as well as the development of new methods. The development of angular differential kernel phases (ADK) that make use the principles of angular differential imaging (ADI), transfering them for kernel and closure phases observables. The experimentation of kernel phases behind shaped pupil apodization masks. The exploitation kernel phases extracted from archival saturated images. The development of architectures for kernel nulling for an arbitrary number of apertures for Fizeau and long-baseline interferometry. These works push the contrast performance of robust observables at small angular separations and begin the exploration of new methods of robust high-contrast observations
Imagerie à haute résolution des amas R136 et NGC3603 dévoilent la nature de leurs populations stellaires by Zeinab Khorrami( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

This thesis aims at studying 2 massive clusters NGC3603 and R136, and the mechanisms that govern their physics, These clusters host the most massive stars known in the local universe so far and are important clues to understand the formation and fate of very massive star clusters. The manuscript outlines the photometric analysis of the core of R136 and NGC3603 on the basis of HST data in the visible and the VLT high dynamic imaging that I obtained in the infrared thanks to the SPHERE focal instrument operated since 2015 and its extreme Adaptive Optics, In an extensive photometric study of these data I discovered a significantly larger number of faint low-mass stars in the core of both these clusters compared to previous works. These stars are often detected in the vicinity of known massive bright objects. By comparing HST and SPHERE measures, NGC3603 does not show any signature of mass segregation in its core since the MF slope of the very core and the next radial bin are similarly flat and agree well with the MF found in previous works of the outer regions. On the other hand R136 is partially resolved using the SPHERE/IRDIS mode with most of the massive stars having visual companions. Considering the spectroscopic and photometric errors on the extinction and the age of cluster members, I estimate a mass range for each detected star. The MF is plotted at different ages with given errors on stellar masses. Finally I demonstrate that we need more resolution to go further on studying R136 which is 7-8 times further than NGC3603
Effet de la turbulence optique sur l'astrométrie solaire par imagerie by Rabah Ikhlef( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

The objective is to understand the effect of optical turbulence on ground-based solar radius measurements. The measurement of the solar radius with accuracy is important for models of solar and stellar structure and evolution. In addition solar activity has an evident influence on the terrestrial climate. The work focused on the calibration and exploitation of data obtained by two telescopes: SODISM2 dedicated to the measurement of the solar radius by full-disk imaging, and MISOLFA a turbulence monitor which allows to estimate the turbulence spatio-temporal parameters. The first measurements of MISOLFA show its capacity for the extraction of turbulence profiles and integrated parameters from the angle-of-arrival fluctuations observed on the solar edge. The spatial parameters estimated from the intensity fluctuations in the pupil plane show a good agreement with the parameters coming from the image plane. The first measurements of the angle-of-arrival characteristic time have also been obtained which give an average value of 5.3 ms over a year of measurements. SODISM2 is the qualification model of an instrument on board the PICARD satellite (2010-2014). The first measurements of this instrument show a high stability and a dispersion of the order of 200 mas (milli-arcseconds). A downward trend on the order of 12 mas/year was also observed but it is not significant given the dispersion of the measurements. A new method was developed for obtaining flat fields using contrast maps. Numerical simulations of imaging through turbulence show a systematic bias introduced by the effect of the turbulence parameters on the estimation of the radius and the limb width
Étude du bulbe galactique avec le Gaia-ESO survey by Álvaro Rojas-Arriagada( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

The Galactic bulge, as a massive and old Galactic component, is key to understand the physicalprocesses responsibles for the formation of the Galaxy. The spectroscopic study of long lived low massstars represents an opportunity to characterize the detailed chemical and kinematical patterns of theeventual mix of stellar populations building up the bulge. In this thesis we made use of data comingfrom the Gaia-ESO survey to conduct a detailed analysis of the disk system as well as bulge stellarpopulations. The bulge metallicity distribution function is bimodal. The metal-rich population exhibitsbar-like kinematics, displays the double RC feature and overlaps the metal-rich end of the thin disksequence in the [Mg/Fe] vs. [Fe/H] plane. We associate these stars with the bar X-shape bulge formedas the product of secular evolution of the early thin disk. On the other hand, the metal-poor populationpresents isotropic hot kinematics and does not participate in the X-shaped bulge. When compared to thethick disk, bulge stars seem to mimic their distribution in the [Mg/Fe] vs. [Fe/H] plane. Whencomparing the metallicity position of the so called ``knee'', that of the bulge is found to be at [Fe/H]=-0.37+/-0.09 dex, being 0.6 dex higher than that of the thick disk. A chemical evolution model suitablyfits the whole bulge sequence by assuming a fast (<1 Gyr) intense burst of star formation taking place atearly epochs. The origin of the metal-poor bulge still remains unconstrained, but further research shouldallow to distinguish between violent processes or secular evolution for its origin
 
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Alternative Names
Centre national de la recherche scientifique (France). Unité mixte de recherche (7293)

J.-L. Lagrange

Lagrange

Lagrange Laboratory facility in Nice, France

Université Côte d'Azur. Laboratoire J.-L. Lagrange

Université Côte d'Azur. Laboratoire Joseph-Louis Lagrange

Université Côte d'Azur. Laboratoire Lagrange

Université Côte d'Azur. Lagrange

Université de Nice-Sophia Antipolis. Laboratoire J.-L. Lagrange

Université de Nice-Sophia Antipolis. Laboratoire Joseph-Louis Lagrange

Université de Nice-Sophia Antipolis. Laboratoire Lagrange

Université de Nice-Sophia Antipolis. Lagrange

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French (15)

English (7)