WorldCat Identities

Dougados, C. (Catherine)

Works: 16 works in 34 publications in 3 languages and 539 library holdings
Genres: Conference papers and proceedings 
Roles: Other, Editor, Author, Thesis advisor, Opponent
Classifications: QB466.J46, 523.01
Publication Timeline
Most widely held works by C Dougados
Jets from young stars : models and constraints by J Ferreira( )

17 editions published in 2007 in 3 languages and held by 514 WorldCat member libraries worldwide

This volume contains the edited lecture notes of the First JETSET School on Jets from Young Stars: Models and Constraints, held by the Marie Curie Research and Training Network on JET Simulations, Experiments and Theory. At this school the lecturers gave an introduction to observational properties and basic models describing the launching and collimation mechanisms of jets. The first half of the book is devoted to general observational constraints, covering the outflow phenomenon in young stars, the identification of magneto-centrifugal processes as the main jet driving mechanism, and the magnetic interaction between the star and its accretion disc. The second half of the book is devoted to theoretical knowledge of magneto-hydrodynamic processes pertinent to the jet launching mechanism in young stars. This comprises a general introduction to magneto-hydrodynamics, a description of the role of MHD processes in Standard Accretion Discs, and the physics of steady state MHD outflows, from the basic concepts and equations to modern self-similar solutions. Further lectures detail the various classes of steady magnetic-wind models currently discussed in the context of protostellar jets
Near-IR [Fe ii] Emission Diagnostics: Disk Winds in Young Stars by N Pesenti( )

1 edition published in 2004 in English and held by 2 WorldCat member libraries worldwide

Formation d'étoiles massives en amas : conditions initiales, origine des masses stellaires et éjections protostellaires by Thomas Nony( )

1 edition published in 2019 in French and held by 2 WorldCat member libraries worldwide

Les recherches que j'ai menées durant ma thèse traitent de trois grands défis en formation stellaire : contraindre par les observations les phases précoces de la formation des étoiles massives - le stade préstellaire, déterminer l'origine des masses stellaires et caractériser les processus d'accrétion-éjection de la phase protostellaire.Dépasser les paradigmes actuels en formation stellaire nécessite d'étudier des régions de formations d'étoiles plus représentatives des processus typiques dans la Voie Lactée. C'est dans ce but que j'ai travaillé sur des observations ALMA de W43-MM1, un jeune proto-amas situé à 5500 pc du Soleil présentant un taux de formation stellaire élevé. J'ai d'abord identifié et caractérisé les cœurs sur la carte continuum. J'ai découvert 131 cœurs avec des tailles typiques de 2400 ua et des masses entre 1 et 100 Msol. La distribution en masse de ces cœurs (CMF) montre au-dessus de 1.6 Msol une pente de -0.96 +/- 0.13 significativement plus plate que celle de l'IMF de référence sur cet intervalle de masse, -1.35. Cela signifie une surabondance de cœurs massifs - et donc d'étoiles massives - par rapport au nombre attendu dans les modèles actuels de formation stellaire. Les explications possibles impliquent soit que la formation d'étoiles est atypique dans W43-MM1 (variabilité dans notre galaxie), soit que les étoiles massives se forment dans les amas sur des échelles de temps différentes des étoiles de type solaire (la formation d'étoiles ne serait pas un processus continu).J'ai ensuite caractérisé ces cœurs en utilisant les raies de CO(2-1) et SiO(5-4) et révélé un riche amas de flots protostellaires constitué de 46 lobes venant de 27 cœurs couvrant tout l'intervalle de masse et incluant 11 cœurs massifs (avec des masses supérieures à 16 Msol ). J'ai aussi utilisé la détection de molécules organiques complexes, des traceurs d'environnements chauds, comme un autre indicateur d'activité protostellaire. 12 des 13 cœurs massifs sont finalement apparus comme étant protostellaires, laissant un seul bon candidat cœur préstellaire massif. Ces statistiques interrogent sur l'universalité de la phase préstellaire pour les cœurs massifs et suggèrent que le modèle du cœur turbulent ne peux s'appliquer partout. Les flots protostellaires permettent aussi de reconstituer l'historique des processus d'accrétion/éjection. J'ai étudié la cinématique des nœuds constituant les jets moléculaires à haute vitesse en utilisant des diagrammes position-vitesse. J'ai montré que la complexité des structures en vitesse de ces nœuds cache une forte variabilité, et évalué le temps caractéristiques entre deux éjections à environ 500 ans. Ces échelles de temps sont similaires à celles mesurés entre deux sursauts d'accrétion pour les étoiles de type FU-Orionis
Etude des cycles d'hystérésis dans les binaires X à trou noir : application à l'objet GX 339-4 by Grégoire Marcel( )

1 edition published in 2018 in French and held by 2 WorldCat member libraries worldwide

The hysteresis behavior of X-ray binaries during their outbursts remains a mystery. In this work, we developed the paradigm proposed in Ferreira et al. (2006) where the disk material accretes in two possible, mutually exclusive, ways. In the standard accretion disk (SAD, Shakura et Sunyaev 1973) mode, the dominant local torque is due to MHD turbulence that transports radially the disk angular momentum. In the jet-emitting disk (JED, Ferreira et Pelletier 1995) mode, magnetically-driven jets carry away mass, energy and all the angular momentum from the disk. Within our framework, the transition from one mode to another is related to the magnetic field distribution, an unknown yet.In this thesis, I have developped a two-temperature plasma code able to compute the thermal balance at each radius for a large ensemble of disk parameters, as well as the self- consistent global emitted spectrum. The radiative cooling term and related spectrum (comptonized bremsstrahlung and synchrotron emission) are obtained using the Belm code (Belmont et al. 2008 ; Belmont 2009). Heating processes are analytical and due only to accretion, while advection is properly taken into account, carrying outside-in the memory of the outer thermal states.Using this code, we have shown that a JED extending along the entire disk nicely repro- duces hard states up to 0.5 Eddington luminosities (Marcel et al. 2018a). It was also shown that JEDs produce a natural hysteresis cycle. However, the global luminosity of the cycle is insufficient and the inevitable presence of jets in JEDs advocates for an inner SAD configuration in soft states.Based on these results, the code was enhanced to solve hybrid configurations with an internal JED and an external SAD, separated by a given transition radius rJ. Playing on both rJ and the accretion rate mdot, we have shown that X-ray observations of typical cycles can be completely covered. Using a simple synchrotron model similar to that of Heinz et Sunyaev (2003), the radio flux produced by the jets can be estimated, showing two important features. First, all radio observations can be covered by our model. Second, the radio flux and X- ray spectral coverages are consistents : parameter sets that reproduce best each spectral state also account for a consistent associated radio flux. For illustration, 5 canonical states from GX 339-4 have been reproduced in X-ray spectral shape and associated radio fluxes (Marcel et al. 2018b).Finaly, using a simple fitting procedure on X-ray spectral shape, the 2010-2011 cycle from GX 339-4 has been reproduced. Strikingly, the co-evolution of rJ and mdot seems to be in adequacy with initial theoretical expectations (Esin et al. 1997). Moreover, the estimated radio flux evolution being close to observations, we decided to use those within the fitting procedure. Adding radio fluxes constraints in the procedure allowed us to reproduce both the associated X-ray spectral shape and radio fluxes with excellent agreement. This is, to our knowledge, the first time that such an accretion-ejection cycle is reproduced. Those results, as well as discussions and implications will be soon submitted
The Origin of Jets from Young Stars: Steady State Disk Wind Models Confronted to Observations by C Dougados( )

1 edition published in 2004 in English and held by 2 WorldCat member libraries worldwide

Modélisation hiérarchique bayésienne des amas stellaires jeunes by Javier Olivares Romero( )

1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide

The origin and evolution of stellar populations is one of the greatest challenges in modern astrophysics. It is known that the majority of the stars has its origin in stellar clusters (Carpenter 2000; Porras et al. 2003; Lada & Lada 2003). However, only less than one tenth of these clusters remains bounded after the first few hundred million years (Lada & Lada 2003). Ergo, the understanding of the origin and evolution of stars demands meticulous analyses of stellar clusters in these crucial ages.The project Dynamical Analysis of Nearby Clusters (DANCe, Bouy et al. 2013), from which the present work is part of, provides the scientific framework for the analysis of Nearby Young Clusters (NYC) in the solar neighbourhood (< 500 pc). The DANCe carefully designed observations of the well known Pleiades cluster provide the perfect case study for the development and testing of statistical tools aiming at the analysis of the early phases of cluster evolution.The statistical tool developed here is a probabilistic intelligent system that performs Bayesian inference for the parameters governing the probability density functions (PDFs) of the cluster population (PDFCP). It has been benchmarked with the Pleiades photometric and astrometric data of the DANCe survey. As any Bayesian framework, it requires the setting up of priors. To avoid the subjectivity of these, the intelligent system establish them using the Bayesian Hierarchical Model (BHM) approach. In it, the parameters of prior distributions, which are also inferred from the data, are drawn from other distributions in a hierarchical way.In this BHM intelligent system, the true values of the PDFCP are specified by stochastic and deterministic relations representing the state of knowledge of the NYC. To perform the parametric inference, the likelihood of the data, given these true values, accounts for the properties of the data set, especially its heteroscedasticity and missing value objects. By properly accounting for these properties, the intelligent system: i) Increases the size of the data set, with respect to previous studies working exclusively on fully observed objects, and ii) Avoids biases associated to fully observed data sets, and restrictions to low-uncertainty objects (sigma-clipping procedures).The BHM returns the posterior PDFs of the parameters in the PDFCPs, particularly of the spatial, proper motions and luminosity distributions. In the BHM each object in the data set contributes to the PDFs of the parameters proportionally to its likelihood. Thus, the PDFCPs are free of biases resulting from typical high membership probability selections (sampling bias).As a by-product, the BHM also gives the PDFs of the cluster membership probability for each object in the data set. These PDFs together with an optimal probability classification threshold, which is obtained from synthetic data sets, allow the classification of objects into cluster and field populations. This by-product classifier shows excellent results when applied on synthetic data sets (with an area under the ROC curve of 0.99). From the analysis of synthetic data sets, the expected value of the contamination rate for the PDFCPs is 5.8 ± 0.2%.The following are the most important astrophysical results of the BHM applied tothe Pleiades cluster. First, used as a classifier, it finds ∼ 200 new candidate members, representing 10% new discoveries. Nevertheless, it shows outstanding agreement (99.6% of the 105 objects in the data set) with previous results from the literature. Second, the derived present day system mass distribution (PDSMD) is in general agreement with the previous results of Bouy et al. (2015).Thus, by better modelling the data set and eliminating unnecessary restrictions to it, the new intelligent system, developed and tested in the present work, represents the state of the art for the statistical analysis of NYC populations
Proper Motions and Velocity Asymmetries in the RW Aur Jet by Luis López-Martín( )

1 edition published in 2004 in English and held by 2 WorldCat member libraries worldwide

Unveiling the Launching Region of YSO Jets with AMBER by Francesca Bacciotti( )

1 edition published in 2003 in English and held by 2 WorldCat member libraries worldwide

Origine et impact des jets/flots protostellaires à l'ère d'ALMA et JWST by Aloïs de Valon( )

1 edition published in 2021 in French and held by 2 WorldCat member libraries worldwide

The formation of a solar-type star is accompanied by spectacular bipolar ejections in the form of atomic jets and molecular outflows. Although these ejections are omnipresent, their exact origin and their impact on the evolution of the protoplanetary disk and the formation of planets within are still major unresolved questions in star and planet formation.Molecular outflow signatures trace colder and slower material. They are historically explained by an interaction between an inner ejection and the surrounding envelope. However, recent observations suggest that these molecular flows trace matter directly ejected from the disk, and consequently could carry away a significant fraction of mass and angular momentum from the forming star-disk system.I had the opportunity to work with observations achieved with the ALMA radio interferometer of the base of molecular flows associated with forming stars at different evolutionary stages. The PhD thesis mainly focusses on the observations of the Class I DG tau B, which increase the angular resolution by more than a factor of 10 with respect to the previous study of Zapata et al. (2015). I also did a preliminary work on the latest observation of the Class II HH30, which improve the sensibility by a factor of 3 with respect to the previous study of Louvet et al. (2018).These observations offer a unique opportunity to study in detail their connexion with the disk and constrain the different models for their formation.The objective of the PhD thesis was to conduct a detailed analysis of the ALMA 12CO emission from the base of molecular outflows and to derive their morphology and kinematics. Innovative analysis methods were developed to search for rotation signatures in particular, based on the pioneering study recently conducted on HH30 (Louvet, Dougados et al. 2018). Observational constraints will be then compared to the different classes of models proposed for their formation to determine whether they originate from the disk or trace interaction with the ambient medium

2 editions published in 1991 in French and held by 2 WorldCat member libraries worldwide

The Origin of Jets from Young Stars: MHD Disk Wind Models Confronted to Observations by C Dougados( )

1 edition published in 2004 in English and held by 2 WorldCat member libraries worldwide

Étude de la population substellaire du Taureau : vers une compréhension du mécanisme de formation des naines brunes by Sylvain Guieu( )

2 editions published in 2006 in French and held by 1 WorldCat member library worldwide

Les naines brunes sont des objets froids, pas assez massifs pour brûler l'hydrogène en leur coeur, comme le font les étoiles de façon stable. Nous en connaissons maintenant plusieurs centaines et leur physique est maintenant bien connue, surtout pour les plus vielle d'entre elles, celles du champs de la galaxie. Pourtant la question de leur formation reste toujours ouverte: comment les nuages moléculaires primordiaux peuvent donner naissances à des objets d'aussi faible masse? Quel est l'influence des paramètres physique de ces nuages sur le mode de formation des naines brunes et sur la quantité ainsi créée? La meilleur voie pour répondre a ces questions est d'étudier les naines brunes jeunes, dans des régions de formation stellaire. Nous avons mené un relevé photométrique grand champ qui a couvert 30 deg2 du nuage du Taureau. Ce relevé profond réalisé dans le domaine visible a été combiné avec un relevé infrarouge proche, puis complété par un suivi spectroscopique pour les candidats optiques les plus prometteurs. Dans ce manuscrit de thèse je décris les étapes de réduction et d'analyse de données photométriques et spectroscopiques. Elles nous ont permit de découvrir et de caractériser de nouvelles naines brunes et étoiles de faible masse dans le Taureau. En étudiant l'ensemble des naines brunes du Taureau et en les comparant aux étoiles nous apportons ici de nouvelles contraintes sur la formation des naines brunes et sur la fonction de masse substellaire dans le Taureau
Vers la détection de planètes à courte période enfouies dans les disques circumstellaires des étoiles jeunes by Kim Pouilly( )

1 edition published in 2021 in French and held by 1 WorldCat member library worldwide

The aim of my thesis is to go toward detection of short-period protoplanets, embedded in the inner region of the disk. The recent detection of a Jupiter-mass planet nearby a young star yields the hypothesis of a formation near the star. However, this region is the place of star-disk interactions, especially magnetospheric accretion, whose observational signatures hide planetary signal. My objective is thus to fully characterize the signatures linked to this phenomenon before be able to study the residuals.The classical T Tauri stars are pre-Main Sequence stars, young stellar objects still accreting materials from their inner disk. Those stars own a strong magnetic field, able to truncate the inner disk at magnetospheric radius and drive the accretion. This phenomenon is called “magnetospheric accretion”. The magnetic pressure on the disk will constrain material to leave the disk plane, forming accretion funnel flows along the magnetic field lines until a localized region at the stellar surface. At this place, the material, which has a velocity near the freefall velocity, will dissipate its kinetic energy on the surface, producing an accretion shock. The shock heats this region, producing a hotter and brighter region called “hot spot”.This region cannot be resolved by direct imaging, and hardly by interferometry, I thus used photometric, spectroscopic and spectropolarimetric time series to characterize those processes using variability analysis. More precisely, I took advantage of spectropolarimetric follow-ups using ESPaDOnS at CFHT close to the Kepler-K2 observations in order to study 2 specific objects: HQ Tauri and V807 Tauri. The quasi-simultaneous campaigns as those ones are difficult to obtain, and is a unique opportunity to compare photometric and spectropolarimetric signatures.The Kepler-K2 light curves allow a precise measurement of the rotation period of the star, and first hypothesis about the structures on those systems as well. I compared the photometric variability with the ESPaDOnS' high-resolution spectroscopy, which provides magnetic information with its spectropolarimetric mode as well, knowing that the structures induced by the magnetospheric accretion process have their own spectroscopic signatures. Furthermore, the magnetospheric radius is usually close to the corotation radius, meaning the radius where the disk's Keplerian period is equal to the stellar rotation period, making those structures rotate at the same period than the star. However, there are still signatures not linked to the magnetospheric accretion which are modulated on stellar rotation period, like dark spots, and signatures linked to the magnetospheric accretion process but not periodic, like magnetospheric ejections which are observed as episodic events during the usual time range of follow-ups. They have to be considered.This project allowed to identify the signatures of magnetospheric accretion, and ascribe them to the different processes, yielding its complete characterization, at least for those 2 objects. This allows to identify unexpected residual signatures as well, for which I proposed some hypothesis asking additional observations to be confirmed
Pièges à poussière auto-induits dans les disques protoplanétaires : du rôle des lignes de gel à la formation des planétésimaux by Arnaud Vericel( )

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

Planet formation relies on dust growth from micrometer sizes through more than 10 orders of magnitude in protoplanetary discs. However, this growth process in hindered by theoretical and experimental barriers. Indeed, on the one hand aerodynamic drag between gas and dust drives the dust radial drift towards the star, which becomes maximum for millimetre to centimetre grains and results in a rapid accretion of the disc onto the star. On the other hand, the relative velocity between grains, which allows them to collide and grow, becomes also the largest for these intermediate sizes, which results in collisions that make the grains fragment rather than grow. Several solutions have been proposed to overcome these barriers, but they often demand particular conditions to operate. Recently, Gonzalez et al. (2017) proposed a solution which combines dust growth, fragmentation and back-reaction onto the gas, i.e. natural elements that can be found in the disc. They called this mechanism 'self-induced dust trap'. My PhD is mainly focused on this particular mechanism and its relationship with other processes that can take place within the disc. These studies have been mainly conducted by means of 3D hydrodynamical simulations using the Smoothed Particle Hydrodynamics (SPH) formalism. Firstly, I focused on the coupled effects of these so called traps with the presence of condensation fronts in discs, called 'snowlines'. These can modify the surface properties of the grains, which impact the way they grow or fragment and can lead to local concentrations of dust. I also looked into the possibility of a disc already hosting a planet and studied its impact on dust evolution. This aspect is particularly interesting regarding the ever-growing number of observations of discs and their structures, the origin of which we need to explain. More specifically, I considered the disc around the star HD 169142, which could carry the signature of dust growth around one planet. I finally invested a lot of my time into the development of numerical methods by implementing a model of dust growth and fragmentation into the public SPH code Phantom and coupling this model with the radiative transfer code Mcfost. I have used this SPH code, which is modern and modular, to compare its results with previous publications and confirm their validity. The implementation of this model could be of use to the community in other studies of dust growth and fragmentation in various systems and to produce synthetic observations
Interactions étoile-disque dans les étoiles jeunes : dippers observés avec K2 by Noemi Roggero( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

Après plus de cinquante ans de recherche sur la formation des étoiles, nous savons que les étoiles de faible masse forment un disque protoplanétaire au cours des premiers stades de leur évolution. C'est à partir de ce disque que se forment les systèmes planétaires. Si les propriétés et les comportements à grande échelle de ces disques sont aujourd'hui observables, la plupart des interactions physiques étoile-disque qui se produisent à des échelles de quelques rayons stellaires sont difficiles à résoudre avec les interféromètres les plus puissants. Entre autres, les modèles d'accrétion induite par la magnétosphère peuvent être sondés indirectement au moyen de la photométrie et de la spectroscopie. Sous certaines conditions, les courants d'accrétion composés de gaz et poussière peuvent produire une diminution épisodique de la brillance de l'étoile. De telles étoiles sont appelées 'dippers' . Cette thèse a pour but d'étudier les étoiles de type dipper dans la région de formation d'étoiles du Taureau, en utilisant des courbes de lumière extrêmement précises fournies par la mission spatiale K2.Tout d'abord, je construis l'échantillon de dippers parmi toutes les courbes de lumière qui sont fournies pour la région du Taureau. J'étudie ensuite la périodicité des creux avec différentes techniques ainsi que leur morphologie. En combinant les données K2 avec les données de la littérature et de plusieurs archives, je fournis des paramètres stellaires afin de sonder plusieurs explications qui ont été proposées pour le phénomène des dippers, en premier lieu l'accrétion magnétosphérique. Confirmant les résultats des études précédentes dans différents amas, les dippers dans la région du Taureau sont très communs, avec une limite inférieure de leur occurrence de ~20-30%. Étant donné les contraintes sur leur observabilité et leur courte durée de vie, les mécanismes à leur origine sont significatifs pour une majorité d'étoiles T Tauri classiques. La plupart des dippers qui présentent des creux comme variabilité prédominante sont quasi-périodiques, avec des périodes de quelques jours qui soutiennent l'hypothèse que le matériau du disque interne contenant de la poussière et l'étoile soient en corotation. L'accrétion magnétosphérique peut expliquer la plupart, mais pas la totalité, des courbes de lumière de cet échantillon de dippers.Enfin, j'applique un modèle de transfert radiatif avec le code MCFOST à JH 223, qui est un dipper prototypique de l'échantillon. Des informations importantes telles que la densité de poussière, la température, la taille de la structure occultante et sa profondeur optique sont dégénérées dans les courbes de lumière observées. Le modèle d'un mur de forme sinusoïdale contenant de la poussière et optiquement épais est capable de reproduire les observations de différents creux irréguliers, avec une variation de la teneur en poussière qui est cohérente avec un taux d'accrétion de masse modéré. De prochaines améliorations dans la modélisation des colonnes d'che contenantes de la poussière et le couplage avec les simulations magnétohydrodynamiques contribueront à fournir une image complète de ce phénomène dans un futur proche
Laboratory astrophysics with magnetized laser-produced plasmas by Benjamin Khiar( )

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

We present in this work different configurations used as a mean to study astrophysically-relevant (by scaling) experiments using laser-produced plasmas and strong magnetic fields. This work is a contribution to the relatively recent field known as high energy density laboratory astrophysics (hedla). The theoretical and numerical framework used in this this work is first introduced with a detailed derivation of the magnetohydrodynamic (mhd) model for bi-temperature and resistive plasmas. The three-dimensional mhd code gorgon and the new physical modules implemented during this thesis are presented. The basic setup studied here involve one or several solid slabs being used as targets for a joule-class laser. The expanding plasma thus produced is embedded in magnetic fields of strengths up to 40 t. Depending on the orientation of the field relative to the target surface, we show that the resulting plasma dynamic, relatively well described by ideal mhd, is strongly modified by the presence of the field. The first topic treated is related to the production, when the field is perpendicular to the target surface, of super-sonic/alfvenic jets relevant in the context of astrophysical jets observed around young star objects (t tauri stars). When the field is oriented parallel to the surface, we show that the configuration results in the formation of thin unstable plasma slabs. We also studied the possibility to generate magnetized accretion shocks in the laboratory and we detail the 3d structure obtained in this case. Alongise the numerical work, we present for each case mentioned previously, new experimental results obtained by the collaboration on the elfie laser facility (luli)
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Jets from young stars : models and constraints
Alternative Names
Dougados, C.

Dougados, Catherine