Rozprawy doktorskie na temat „Grains de poussières”
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Racković, Babić Kristina. "Détection in-situ de poussières à l'aide d'antennes radio sur plusieurs sondes spatiales : observations et modèle". Electronic Thesis or Diss., Université Paris sciences et lettres, 2022. http://www.theses.fr/2022UPSLO015.
Pełny tekst źródłaInterplanetary dust grains contain important information about the Solar System. Analyzing these particles is an important aspect of the heliosphere study. Dust impacts have been observed using radio and wave instruments onboard the spacecraft since the 1980s. The interaction between the impact-generated plasma cloud and antenna – spacecraft system elements generates the characteristic signal waveform. The present work focuses on the detection and interpretation of the dust generated signals from radio instruments onboard various spacecraft orbiting at 1 AU.In the first part of the thesis, we aim to develop a model which links the observed electric signals to the dust impact properties. We propose a new model which takes into account the effect of impact - ionization charge collection and electrostatic-influence. Our model provides an analytical expression for the pulse. It allows us to measure the amount of total ion charge, the fraction of escaping charge, the rise timescale, and the relaxation timescale. The proposed model is simple and convenient for large data fitting. To validate the model, we use the Time Do- main Sampler (TDS) subsystem of the STEREO/WAVES instrument, which generates high-cadence time series of voltage pulses for each monopole. Since the beginning of the STEREO mission in 2007, we have collected all the dust events detected by S/WAVES/TDS simultaneously on all three monopoles at 1 AU. Our study confirms that the rise time vastly exceeds the spacecraft’s short timescale of electron collection by the spacecraft. Aside from electron dynamics, we also obtained interesting results regarding the cloud’s electron temperature. The presented model provides an effective tool for analyzing dust waveforms, and is applicable for different space missions which investigate the distribution of dust particles, e.g., Solar Orbiter and Parker Solar Probe.In the second part of the thesis, we focus on the interstellar dust (ISD). Interplanetary and interstellar dust are the two main dust populations at 1 AU. Our objective is to search for interstellar dust by analyzing the data sets collected by STEREO and Wind, starting from the beginning of the missions. Between 2007 and 2012, while being at the solar minimum with a solar dipole pointing southward, all three spacecraft recorded ISD flux at 1 AU. However, before and after that period, the disappearance of the interstellar component was noticeable. The observed change of the impact rate suggests that the flux of interstellar dust at 1 AU varies with the solar cycle. Each time the magnetic dipole field changes its polarity during the solar cycle, small interstellar grains experience focusing or defocusing. Consequently, the dust grains are systematically deflected either towards, or away from the solar magnetic equator plane by the solar wind magnetic field which thus affects the dust dynamics and the total interstellar dust flux in the inner heliosphere. Our study provides the first quantitative description of the time variation of ISD flux at 1 AU
Cavarroc, Marjorie. "Nucléation, croissance et comportement de poussières dans les plasmas réactifs radiofréquence basse pression : Des nanocristaux aux grains submicroniques polycristallins". Phd thesis, Orléans, 2007. http://www.theses.fr/2007ORLE2029.
Pełny tekst źródłaBot, Caroline. "Le milieu interstellaire et le cycle des grains dans le Petit Nuage de Magellan". Phd thesis, Université Louis Pasteur - Strasbourg I, 2005. http://tel.archives-ouvertes.fr/tel-00152441.
Pełny tekst źródłaMes travaux sont consacrés en particulier à la définition des propriétés des poussières, du milieu diffus aux régions de formation stellaire du SMC. L'analyse et la modélisation de l'émission infrarouge dans ces environnements montre que (1) les grains sont globalement détruits dans le milieu diffus; (2) la destruction des PAHs ne serait pas systématique dans le MIS de faible métallicité.
La seconde partie est dédiée à l'étude de l'émission millimétrique des poussières comme traceur du gaz moléculaire dans les nuages denses. La comparaison de ce traceur avec l'émission CO indique une dépendance linéaire avec la métallicité du facteur de conversion CO-vers-H$_2$. D'autre part, les masses de nuages moléculaires locaux déduites de ce traceur sont compatibles avec celles obtenues à partir des observations CO. Cependant, dans le SMC on observe un excès systématique par rapport aux masses virielles. L'ajout d'un champ magnétique comme support partiel de ces nuages permet d'expliquer l'excès observé.
L'ensemble de mes travaux met en évidence une évolution du rapport gaz-sur-poussières dans le SMC. Dans le milieu diffus, les grains sont détruits par les nombreuses explosions de supernovae. Les éléments lourds réaccrètent sur les grains dans les régions plus denses.
Ces études se placent comme cas scientifiques d'utilisation de l'Observatoire Virtuel (OV). Dans ce cadre, j'ai construit une base de données sur les nuages de Magellan, prototype des bases de données d'équipe de l'OV. De plus, la formalisation des étapes de traitement et d'analyse effectuées me permet de spécifier les développement nécéssaires à l'inclusion des objets étendus dans l'OV et de proposer des outils génériques.
Palomba, Ernesto. "Mesure du flux de poussières émises par la comète 46P/Wirtanen dans le cadre de la mission spatiale ROSETTA". Aix-Marseille 1, 2001. http://www.theses.fr/2001AIX11053.
Pełny tekst źródłaFanciullo, Lapo. "Nouveaux aperçus sur les propriétés des poussières à partir des données Planck en intensité et polarisation". Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS194/document.
Pełny tekst źródłaInterstellar dust is a key component of the interstellar medium (ISM). Not only does it play an important role in thephysics and chemistry of the ISM, but its thermal emission can be used to trace the gas column density, and itspolarization angle to trace the magnetic field orientation projected on the plane of the sky.Different dust models have been built to reproduce the main dust observables: extinction curve and albedo, spectralenergy distribution (SED) from the near-infrared to the microwave continuum, polarization in extinction and emission,within cosmic elemental abundance constraints. Our understanding of interstellar dust is, however, still incomplete;among other things, we do not fully understand the local variations in the emission and extinction properties of dust.The variation of the dust far-infrared opacity from the diffuse ISM to molecular clouds is well established, and modelshave been proposed. With the Planck submillimeter survey we have, for the first time, a multi-wavelength, all-sky mapof dust emission allowing for a precise measure of dust temperature, and therefore of dust opacity variations in thediffuse ISM.This thesis, based on the comparison of Planck data with extinction measures toward stars and QSOs, makes use of bothdust models and data analysis to constrain the dust optical properties and evolution within the diffuse ISM, and toimprove our understanding on the interplay between grain alignment and dust optical properties in the emission ofpolarized thermal radiation.The first half of the thesis focuses on the total emission of dust in the diffuse ISM. The variations in the ratio of dustemission to extinction is used to constrain the variations of the dust optical properties. We fit the 20 SEDs normalizedper unit extinction of Planck intermediate results XXIX with three dust models (Draine & Li 2007, Compiegne et al2011, Jones et al 2013). The best agreement between model and observations is obtained for the model with the moreemissive grains (Jones 2013), with optical properties derived from recent laboratory data on silicates and amorphouscarbons. We develop a new estimator of the radiation field intensity G0, which combines the dust SED and theextinction on the same line of sight. We show that this new estimator is less biased than the one obtained through thefitting of the dust SED. With their fixed optical properties, none of the models can simultaneously reproduce thevariations of G0 and of the shape of the SED. With our new estimator of G0, we demonstrate that the variations in thedust optical properties and in the radiation field intensity give similar contributions to the scatter observed in the dustSED per unit extinction in the diffuse ISM.The second half of the thesis focuses on polarized dust extinction and emission in molecular clouds. By confrontingPlanck and stellar observations to a dust model, we attempt to disentangle the effects of variations in the dust opticalproperties from the effects of variations in the grain alignment. We find a correlation between the ratio of polarizedemission to polarized extinction, RP/p = P353/pv, and the wavelength of maximum polarization in extinction, λmax, whichtraces the typical size of the aligned grains. Using a new dust model for polarization based on Planck data, we show thatthe variation of the minimal size of aligned grains can reproduce the observed correlation, without any need for achange in the size distribution or in the optical properties of grains. This scenario is also compatible with the drop of thefractions of polarization with λmax. Alternative models cannot however be ruled out
Perrin, Jean-Marie. "Contribution à la théorie de la diffusion de la lumière par des grains : Application à l'interprétation de la diffusion du rayonnement solaire par les poussières interplanétaires". Aix-Marseille 1, 1987. http://www.theses.fr/1987AIX11086.
Pełny tekst źródłaBarriere-Fouchet, Laure. "Distribution des grains de poussière dans les disques protoplanétaires". Lyon, École normale supérieure (sciences), 2005. http://www.theses.fr/2005ENSL0314.
Pełny tekst źródłaStepnik, Bertrand. "Émission submillimétrique du milieu interstellaire : coagulation des grains". Paris 6, 2001. http://www.theses.fr/2001PA066529.
Pełny tekst źródłaBouet, Christel. "Modélisation multi-échelle de la dynamique des panaches d'aérosols naturels en Afrique". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2007. http://tel.archives-ouvertes.fr/tel-00311058.
Pełny tekst źródłaCette étude a été réalisée à l'échelle méso haute résolution en utilisant le modèle Regional Atmospheric Modeling System (RAMS) couplé en ligne avec le Dust Production Model (DPM) développé par Marticorena et Bergametti [1995] et Laurent [2005]. Afin d'examiner la capacité de ce modèle à reproduire les émissions d'aérosols minéraux dans la région complexe de Bodélé, nous avons tout d'abord modélisé la période correspondant à la campagne Bodélé Dust Experiment 2005 (BoDEx 2005). Notre modèle a ainsi été capable de reproduire les caractéristiques météorologiques locales (principalement le vent dans les basses couches) ainsi que les concentrations en aérosols minéraux et la structure du panache observées pendant la campagne. Nous avons aussi vérifié que les aérosols émis depuis cette région du monde atteignent le continent sud américain.
De plus, cette validation nous a permis de vérifier le constat établi par divers auteurs : les modèles à grande échelle (MCG) ont souvent du mal à reproduire correctement les champs de vent dans la région de Bodélé. Nous avons alors entrepris une étude climatologique (sur l'année 2001) sur une zone étendue autour de la région de Bodélé à différentes résolutions spatiales afin de caractériser les phénomènes de basses couches qui pourraient expliquer ce biais quasi-systématique des MCG. Ce travail a été validé grâce aux données de routine des stations de mesure de surface ainsi que grâce à l'imagerie satellite.
Le deuxième cas sur lequel la validation de notre outil était nécessaire est constitué par les événements de ligne de grains qui se succèdent sur la zone sahélienne lors de l'été boréal. Cette validation a été réalisée sur un événement bien documenté des périodes d'observations spéciales 1 et 2 de la campagne Analyse Multidisciplinaire de la Mousson Africaine (AMMA).
Buttice, Vincent. "Caractérisation et étalonnage de la caméra de l'expérience ballon PILOT (Polarized Instrument for Long wavelength Observation of the Tenuous interstellar medium)". Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00946880.
Pełny tekst źródłaBouet, Christel. "Modélisation multi-échelle de la dynamique des panaches d'aérosols naturels en Afrique". Phd thesis, Clermont-Ferrand 2, 2007. http://www.theses.fr/2007CLF21790.
Pełny tekst źródłaMerouane, Sihane. "Etude en laboratoire de grains extraterrestres et de leurs analogues de synthèse". Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00925675.
Pełny tekst źródłaBoehler, Yann. "Étude du grossissement et de la distribution spatiale des grains de poussière dans les disques protoplanétaires". Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14146/document.
Pełny tekst źródłaThe stars, during the first millions years of their existence, are surrounded by a protoplanetary disk composed of99 % of gas and of 1 % of dust. The dust is initially under the form of sub-micrometric grains but evolves to likelyform planets. Thanks to the Plateau de Bure interferometer, with whom we observed at the millimeter wavelengths, the temporal evolution as well the radial distribution of the dust grains has been bringing to light in several disks.In addition, the important gain in resolution and in sensibility of ALMA, a new interferometer based in Chili, has required the improvement of our transfert radiativ code in order to determine if and how it will be possible to observe the dust settling, preliminary step for the formation of planetesimals
Nguyen, Thanh Hoang Phuong. "Etude expérimentale de la désorption et de la réactivité des espèces azotées sur les grains de poussière interstellaire". Thesis, Cergy-Pontoise, 2018. http://www.theses.fr/2018CERG0977/document.
Pełny tekst źródłaThe interstellar medium is a key component of galaxies which is the matrixof the formation of stars and planets. It is composed of interstellar gas and dust grains. The presence of complex organic molecules (COMs) can be understoodvia reactions in the gas phase. However, the synthesis of some key species (i.e H2, H2O, CO2, etc) needs the intervention of the solid-state reactions on dust grains surface. More than 200 molecules including COMs have been detected in ISMand circumstellar shells. Some of these COMs already contain carbon, oxygen,and nitrogen, which are the main chemical elements in the composition of themolecules on which terrestrial life is built. The aim of this thesis is to understand physical and chemical processes (i.e diffusion, desorption, and reactivity) occurring on interstellar dust grains. More specifically, my thesis focuses on the investigation of desorption and reactivity of nitrogen bearing species that lead to COMs by hydrogenation related processes.All experiments were performed with the VENUS set-up located at the LERMACergy laboratory in the university of Cergy Pontoise, France. VENUS is composedof an Ultra High Vacuum (UHV) chamber, so called the main chamber, with abasis pressure around of 10 −10 mbar. Atoms/molecules were injected onto a sample holder in the UHV chamber through a separated four beamline system. The sample holder is controlled in temperature from 7 K to 400 K. Products are probed by using mass spectrometer and reflection adsorption infrared spectroscopy. Different solid states environments have been used: gold surface or water ice substrates (compact amorphous solid water, porous amorphous solid water, and crystalline ice) to mimic different the astrophysical environments.We proceeded experiments involving some atoms and molecules such as hydrogen,deuterium, oxygen, CO, N2, NO, H2O, H2CO, CH3CN, and CH3NC. These specieswere deposited on the cold surface held at 10 K (up to 40 K). CO and N2 weredeposited on water ice substrates to study different adsorbed behaviours as well as the distribution binding energy and the segregation mechanism. We studied theefficiency of atoms (i.e oxygen and hydrogen) penetration into porous water ice.We used NO as a chemical tracer for the penetration of O and H atoms throughwater ice. From the analysis of the consumption of NO, we estimated the penetra-tion of O or D atoms through porous water ice. We proceed new experiments onthe hydrogenation of NO and found that there is an activation barrier at HNO H step. However, H atoms can cross the activation barrier via quantum tunnelingon the cold surface maintained at 8 K. We indicated that hydroxylamine (NH2OH)is the major product of the hydrogenation of NO at low temperatures, but N2O isthe major product at high temperatures. We also present possible chemical path-ways of the pre-biotic formamide (NH2CHO) through the co-hydrogenation of NOand H2CO on the cold surface (typically at 10 K). Simultaneously, we analysedand discussed the efficient formation route of formamide on interstellar grains. We showed that the chemical network of the hydrogenation of CH3CN and CH3NC iscomplex and takes place via different mechanisms which tend to be competitive.We measured and indicated that the hydrogenation is the dominant mechanism.Furthermore, H2O is always raising the reactive efficiency
Matar, Elie. "Interaction de l'hydrogène atomique et moléculaire sur des surface de glace d'eau amorphe simulant les grains de poussière interstellaire". Phd thesis, Université de Cergy Pontoise, 2009. http://tel.archives-ouvertes.fr/tel-00438534.
Pełny tekst źródłaGarcia, Anthony. "Évolution de la porosité des grains : une solution aux problèmes de formation planétaire ?" Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1142/document.
Pełny tekst źródłaIn protoplanetary discs, micron-sized grains should grow up to planetesimal sizes in order to ultimately form planets. However, dynamical studies show that once they reach a critical size, they drift rapidly into the accreting star. This is known as the radial-drift barrier. Moreover, laboratory experiments have shown that grains can fragment or bounce, stopping the growth towards planetesimal sizes.In order to overcome those barriers, several methods have been proposed such as particles traps (e.g. vortices or planet gaps) which all involve large-scale dynamics.In this work, we choose to investigate the intrinsic properties of the grains during their growth, in particular their porosity.We thus consider the growth of grains with variable porosity as a function of their mass in several regimes of compression/expansion (Kataoka et al. 2013, Okuzumiet al. 2012) and implement it in our 3D SPH two-fluid code (Barrière-Fouchetet al. 2005).We find that growth is accelerated for porous grains that can reach kilometersizes. On the other hand, drift is slightly slowed down for porous grains that can grow up to larger sizes before drifting towards the star. As a result, grains in the outer regions of the disc reach larger sizes than when porosity is neglected. Those two mechanisms can help grains overcome the radial-drift barrier and form planetesimals.The Stokes drag regime appears to play a substantial part in maintaining grains in the disc.Considering a constant fragmentation threshold, we also find out that growth is delayed because of fragmentation but reaching large sizes and thus overcoming problems due to fragmentation and radial drift is still possible. However, very fluffy grains are fragile and can be easily disrupted leading to a massive accretion of dust into the star. Moreover, we show that the effects due to dust bouncing can be neglected compared to fragmentation.Finally, we investigate the influence of the size of monomers and -parameter on the evolution of porosity and then dust in the disc.Dust growth is accelerated by porosity and thus promotes grains decoupling. Very fluffy grains are more affected by fragmentation. However, dust collective effects and porosity can help grains to overcome planet formation barriers. Besides,the bouncing barrier can be neglected in the case of porous dust compared to other barriers. Finally, the intensity of turbulence can alter the growth and so the outcome of dust. The size of monomers modifies the grain filling factor without impacting dust decoupling in the inner parts of the disc
Boudet, Nathalie. "Etude de la matière interstellaire : Caractérisation de l'émission des grains". Phd thesis, Université Paul Sabatier - Toulouse III, 2005. http://tel.archives-ouvertes.fr/tel-00009589.
Pełny tekst źródłaMinissale, Marco. "Physique et Chimie sur la surface de la poussière interstellaire : effet de la diffusion des atomes d’oxygène et de la désorption chimique sur le réseau chimique H-C-N-O". Thesis, Cergy-Pontoise, 2014. http://www.theses.fr/2014CERG0721/document.
Pełny tekst źródłaThe interstellar medium is the matter that exists in the space between the star systems in a galaxy. It is composed of gas and elongated tiny dust grains. To date, plenty of molecules (> 170) are known to exist in the interstellar medium. The presence of most of them can be understood in terms of gas phase reactions but the synthesis of some key species (H2, H2O, CO2) need the intervention of solid-state reactions on dust grains surface. The aims of this thesis are to understand what are the relevant physical-chemical processes (i.e., diffusion and desorption) occurring on the surface of interstellar dust grains and how these processes influence synthesis of more and more complex molecules. In particular, the focus of my thesis is the investigation of:1) the role of O-atom diffusion and the oxidation processes in the formation of interstellar ices;2) the thermal and non-thermal processes coupling gas and solid phase.The reasons of these investigations lie on the realization that, up to now, only hydrogen diffusion and hydrogenation reactions are commonly considered in solid astrochemistry and the role of oxygenation as well as the importance of adsorption and desorption processes are often disregarded.Evidently, a better knowledge of such physical-chemical processes and, in general, of the solid state physical-chemistry could help astronomers to understand the formation of interstellar ices, the increase on molecular complexity, and the equilibrium between gas and solid phase.To answer these questions, many experiments have been performed with the FORMOLISM set-up, i.e., FORmation of MOLecules in the ISM, located in the Universitè de Cergy Pontoise, Observatoire de Paris. Via two triply differentially pumped beams, atoms and molecules were aimed at a cold (>6.5 K) sample held in a Ultra high vacuum chamber. The products were probed using Mass spectroscopy and Reflexion Absorption Infrared Spectroscopy.To simulate different astrophysical environments, the solid state physical-chemistry has been studied in different experimental conditions:-The substrate morphology (Amorphous water ice, porous (p) and compact (np), crystalline (c) ice, amorphous silicate, and graphite)-The species deposited and their relative ratio-The coverage of deposited species, from 0.1 to 2 ML-The substrate temperature, from 6.5 to 60 KConcerning oxidation processes and O-atom reactivity, the results show that oxygen is very reactive with many species (i.e., H, CO, NO, H2CO, HCOOH); O diffusion appears to be much faster than previously expected and can occur via quantum mechanical tunnelling at temperatures as low as 6.5 K. We compared the experimental values of the diffusion coefficients and found that the rates of diffusion on each surface, based on modelling results, were considerably higher than those expected for heavy atoms such as oxygen. Our findings show that O atoms can scan any available reaction partners (e.g., either another H atom, if available, or a surface radical like O, OH, CO) at a faster rate than that of accretion. In particular, in very dense interstellar clouds, the O/H ratio is such that O becomes one of the dominant reactive partners together with H. This has an impact on the chemistry occurring at the surface of dust grains as either the formation of some species may be enhanced, or at least the relative abundances of the final products will be affected. An important example of how O-atom mobility can modulate the abundances of key species of ices in the ISM is the case of the H2O/CO2 ratio via the CO+O and H2CO+O pathways.Concerning gas-solid coupling processes (i.e., adsorption, sticking, thermal desorption, chemical desorption), the results show that each processes is influenced in a different way by the substrate (i.e., water ice, silicate or graphite). Moreover, we provide a useful list of binding energies of several species and chemical desorption efficiency for different reactions on different subst
Santandrea, Audrey. "New insights on the explosion severity of nanopowders : a nano-grain of sand in the gears of the standards". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0104.
Pełny tekst źródłaThe small size of nanoparticles implies a high specific surface area, which induces original properties when compared to micropowders, such as chemical, mechanical, optical or biological properties. Among these new specificities, nanoparticles are subjected to weak cohesion forces, such as van der Waals, electrostatic or capillary forces, which cause them to agglomerate in a reversible way. However, dust explosions require the dispersion of the dust in the air, which can lead to a breakage of these agglomerates. The aim of this work is then to study the influence of nanoparticles specificities, notably the agglomeration, on their ignition sensitivity and explosion severity, and evaluate the adequacy of the international standard methods to determine these parameters when it comes to nanoparticles. Four types of powders were chosen to highlight the specific behavior of each type of combustible powder: carbon black, nanocellulose, aluminum and carbon-coated silicon. The powders were characterized by Scanning Electron Microscopy (SEM), specific surface measurement and helium pycnometer, and their particle size distribution (PSD) was measured before and after dispersion using different methods. The mean surface diameter, used to consider the high surface area of nanoparticles, considerably decreases after the injection in the 20L sphere, i.e the standard equipment to measure the explosion severity of a dust. This observation highlighted the necessity to characterize the dust after injection in the 20L sphere, to accurately evaluate the explosion risk. Ignition and explosion tests were conducted in standard conditions, but also by varying the powder preparation (aging, drying, sieving, agglomeration), and the operating conditions (dispersion procedure, ignition energy, initial turbulence). Specific behaviors related to the powder nature (carbonaceous, organic or metallic) were then observed, discussed, and alternative measurement methods were proposed. For instance, alternative dispersion nozzles were tested to provide a better cloud homogeneity or to reproduce industrial release conditions. Dispersion procedure and ignition source should be adapted to the minimum ignition energy of the nanopowders to avoid both pre-ignition and overdriving. Variation of the ignition delay time can be helpful to obtain the most conservative results. One of the main proposals consists in the consideration of the laminar burning velocity as a standard characteristic of the explosion severity. Experiments were conducted in a flame propagation tube and a vented 20L sphere to evaluate the unstretched burning velocity of nanocellulose. The results were then compared to an existing correlation based on the pressure-time evolution during standard experiments. Furthermore, a flame propagation model, initially designed for hybrid mixtures, was adapted to the flame propagation in a cloud of organic nanoparticles, showing consistent results with the experiments
Rémy-Ruyer, Aurélie. "Probing the impact of metallicity on the dust properties in galaxies". Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112340/document.
Pełny tekst źródłaAs galaxies evolve, their Interstellar Medium (ISM) becomes continually enriched with metals, and this metal enrichment influences the subsequent star formation. Low metallicity dwarf galaxies of the local Universe are ideal candidates to study the influence of metal enrichment on the ISM properties of galaxies and gives us insight into the enrichment process and star formation under ISM conditions that may provide clues to conditions in early universe metal-poor systems. Previous studies have shown that the ISM of dwarf galaxies poses a number of interesting puzzles in terms of the abundance of dust grains, the dust composition and even the FIR emission processes. However these studies were limited to the warmer dust emitting at wavelengths shorter than 200 microns and were done only on a small number of dwarf galaxies. Thanks to its increased sensitivity and resolution in FIR and submillimeter (submm) wavelengths, Herschel gives us a new view on the cold dust properties in galaxies and enables us to study the lowest metallicity galaxies in a systematic way. In this work, I carry out a study of the dust properties in dwarf galaxies and compare with more metal rich environments, in order to address the question of the impact of metallicity on the dust properties. The novelty of this work lays in the fact that dwarf galaxies are studied here in a systematic way, enabling us to derive and quantify the general properties that are representative of these systems. This study is conducted over the full IR-to-submm range, using new FIR/submm Herschel observations, Spitzer, WISE, IRAS and 2MASS data. We complete this set of data with longer submm measurements from ground-based facilities such as APEX and JCMT to study the presence and characteristics of the submm excess in my sample of galaxies. I also collect Hi and CO data to access the gas properties of the galaxies and study the evolution of the G/D with metallicity. Our study reveal different dust properties in low-metallicity environments than that observed in more metal-richs systems (e.g., an overall warmer dust component). An excess submm emission is often apparent near and/or beyond 500 microns rendering large uncertainties in the dust properties, even for something as fundamental as dust masses. Some of the smallest excesses can be explained by using another dust composition with more emissive grains. Ideal tracer of the chemical evolutionary stage of a galaxy, the gas-to-dust mass ratios (G/D) is found to be much higher than what is expected by simple chemical evolution models. Interpreted with more sophisticated chemical evolution models, including dust growth in the ISM and/or episodic star formation, the relation of the G/D with metallicity and its scatter can be explained by the wide variety of environments we are considering
Leiton-Thompson, Roger. "Resolving the cosmic infrared background with the Herschel space observatory". Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112146.
Pełny tekst źródłaDuring the last decades, infrared astronomy has changed our view about the evolution of galaxies, especially at large distances. We have access to large variety of physical information in the infrared bands. However, diffraction limits of the infrared instruments and the existence of a large number of sources makes individualization of galaxies a difficult task. The first part of this thesis is entitled Resolving the Cosmic Infrared Background with the Herschel Space Observatory where, by the use of far-infrared realistic simulations of the deepest infrared images of the Universe, we have studied the origin of the confusion noise in the GOODS-Herschel images and resolved a substantive part of the Cosmic Infrared Background into individual galaxies. New techniques were developed to predict the fluxes in the far-infrared from prior knowledge in the mid-infrared. Mock images were built using those predicted fluxes to evaluate the role of local confusion noise and identify individual sources. The second part of the thesis concerns the study of the Destruction of dust grains by radio jets. We study the effects of active galactic nuclei in the insterstellar medium, in particular in the mechanism that gives rise to the narrow-line region in Seyfert galaxies. Long-slit near-Infrared spectra of a set of type-2 Seyfert galaxies were taken to measure diagnostic emission lines ([Fe II], [P II] and Paβ) that reveal the destruction of dust grains due to the shock waves produced by the radio jets. We found that the dominant mechanism of ionization close to the nuclei of the Seyfert galaxies is the radiation field produced by the back hole activity. In the outer part of the narrow-line region, shock waves induced by the radio jets also contribute to the energy budget of the interstellar medium and sputter the dust grains. This was a co-advising thesis performed in the Service d’Astrophysique CEA-Saclay and the Astronomy Department of the University of Concepción, Chile
Durante las últimas décadas, la astronomía infrarroja ha cambiado nuestra visión sobre la evolución de galaxias, en especial revelando que a grandes distancias (z >1) las galaxias individuales son típicamente Galaxias Infrarrojas Ultraluminosas (cuyas siglas en inglés son ULIRGs por Ultraluminous Infrared Galaxies, 1012 < Lbol < 1013 L⊙). Actualmente tenemos acceso a una gran variedad de información física basada en la emisión en bandas espectrales infrarrojas (IR), radiación que en el caso de las galaxias es producida en su mayoría por granos de polvo. Sin embargo, el límite de difracción de los instrumentos infrarrojos junto con el gran número de fuentes de emisión hace de la individualización de galaxias una tarea difícil. La primera parte de esta tesis se titula Resolviendo el Fondo Cósmico Infrarrojo con el Observatorio Espacial Herschel donde, con el uso de simulaciones realistas de las imágenes más profundas del Universo, hemos estudiado el origen del ruido de confusión en las imágenes GOODS-Herschel y resuelto en galaxias individuales una parte sustantiva del Fondo Cósmico Infrarrojo. Nuevas técnicas fueron desarrolladas para predecir los flujos en el infrarrojo lejano a partir del conocimiento a priori en el infrarrojo medio. Las imágenes simuladas fueron construidas usando esos flujos predichos y con ellos evaluar el rol del ruido de confusión local así como identificar fuentes individuales. La segunda parte de la tesis trata del estudio sobre la Destrucción de granos de polvo por chorros en ondas de radio. Este proyecto que se concentró en la observación de galaxias Seyfert y ULIRGS y apunta a entender mejor el ciclo de vida del polvo al estudiar la destrucción de granos en galaxias con nucleos activos y los efectos de la actividad de estas últimas en el medio interestelar, en particular en el mecanismo que da origen a la región de líneas de emisión angostas en las galaxias Seyfert. Se obtuvo espectros infrarrojos de rendija larga de galaxias Seyfert del tipo 2 para medir líneas de emisión ([Fe II], [P II] y Paβ) las cuales revelan la destrucción de granos de polvo debido a las perturbaciones de las ondas de choque producidas por chorros detectados en ondas de radio. Hemos encontrado que el mecanismo dominante de la ionización cerca de los núcleos de las galaxias Seyfers es el campo de radiación producido por la actividad del agujero negro central. En la parte externa de la región de líneas de angostas, las ondas de choque inducidas por los chorros en radio también contribuyen al balance energético del medio interestelar y desintegran los granos de polvo. Esta fue una tesis de co-tutela llevada a cabo en el Departamento de Astronomía de la Universidad de Concepción y en el Service d’Astrophysique del Commissariat á l’Énergie Atomique (CEA), Francia
Jallat, Aurélie. "Fragmentation de molécules carbonées d'intérêt astrophysique auprès des accélérateurs". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112204.
Pełny tekst źródłaNowadays, about 200 molecules have been observed in the interstellar medium, about 75% are carbon molecules and 25% hydrocarbons. Dust grains also contain carbon in large quantities. The presence of carbon in the majority of molecules of the gaseous phase and in the dust is due to its abundance and its ability to form bonds. So, it is crucial to study the carbon in an astrochemical point of view.In the first part, this work presents measurements of branching ratios and energy dissipated as kinetic energy in neutral fragments which are emitted in a high speed collision, of the following carbon molecules: SiC, AlC, AlCH, C ₂ O, CN, CH ₂ and CH. These measurements were obtained from the experimental setup AGAT. This setup is permanently installed at the Tandem Orsay facility. It allows molecule-atom collisions and 100% effective detection of all the transmitted fragments, including neutral ones.In the second part, the effect of the addition or correction of new hydrocarbon branching ratios is discussed, by modeling of chemistry of two famous objects: the photo-dissociation region of the Horsehead nebula and the molecular cloud TMC-1. Both objects are well known for their numerous observed molecules. These new branching ratios reduce the calculated abundances of species in the gas phase, even though these abundances were already too low compared to the observations. A hypothesis states that hydrocarbons are released into the gas phase via the carbonaceous interstellar dust. Following this assumption, for the first time, the effects of the incorporation of photo-production reactions of hydrocarbons from the hydrogenated amorphous carbons were studied on the chemistry of the gaseous phase of the Horsehead nebula. The addition of these reactions narrows the gap between modeling and observations
Lebreton, Jérémy. "Observations et Modélisation des systèmes planétaires autour des étoiles proches". Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00876169.
Pełny tekst źródłaDjebli, Mourad. "Expansions des Plasmas poussiéreux en géométrie sphérique". Phd thesis, 2004. http://tel.archives-ouvertes.fr/tel-00008298.
Pełny tekst źródłaPoidevin, Frédérick. "Analyse multi-échelle des champs magnétiques dans des nuages moléculaires à structures filmentaires". Thèse, 2006. http://hdl.handle.net/1866/2818.
Pełny tekst źródłaTogether with other observational methods, visible and near infrared polarimetry can help tu understand the morphology of magnetic fields in the neighborhood of several star-forming regions. inside molecular clouds, this morphology can be deduced with the help of submm polarimetry but rarely in the same regions. When both observational methods are used for the same region, there is a gap in the spatial scales to correctly compare the Galactic magnetic field with the magnetic field probed inside the clouds. -- This thesis proposes the necessary steps to make this type of multi-scle analysis and to better understand the role that can be played by magnetic fields in stellar formation regions. The GF 9 region is the first region analysed with this method. Then, a study of the morphology of the magnetic field located in filamentary molecular clouds OMC-2 and OMC-3 is presented, followed by a multi-scale analysis of the Orion A region, the molecular cloud complex in which these clouds are embedded. -- The results covering both regions can be summarized as follows. it is statistically shown that the large scale morphology of the field is poloidal in the GF 9 region, and probably toroidal in the Orion A complex. On the smaller spatial scale of the envelopes of the clouds, the magnetic fields appear to be aligned with the fields at their periphery. On the spatial scale of the cores, the poloidal magnetic field located in the vicinity of GF 9 is apparently twisted and entrained by the rotation of the core and ambipolar diffusion does not seem to be effective at the present time. In Orion A, the morphology of the fields can hardly be probed in active sites of stellar formation in OMC-2, and is strongly constrained by the effects of gravity in OMC-1. There is no evidence for turbulence in all the observed regions. -- All in all, the multiscale analyses suggest that independently of the evolutionary state or of the range in mass of the star-forming regions, the magnetic field morphology is significantly affected on spatial scales similar to those of cores, in the same way that molecular clouds properties remain self-similar down to the spatial scales similar to those of cores.
Conseil de recherche en sciences naturelles et en génie du Canada