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Lombardo, Linda. "Explorer l'histoire de la Galaxie grâce à la spectroscopie stellaire". Electronic Thesis or Diss., Université Paris sciences et lettres, 2022. http://www.theses.fr/2022UPSLO011.
Pełny tekst źródłaThis thesis project presents several studies that are focused on the investigation of the chemical properties of different stellar populations in the Milky Way by means of high-resolution spectroscopy.The thesis is structured as follows:The first chapter is an introduction to the thesis project, and is divided into three sections. The first section describes the structure and formation scenarios of the Milky Way, in particular by referring to the most recent discoveries. The second section introduces the basic concepts and objectives of the studies presented in this thesis work. The third section describes the methods used to analyse the spectroscopic data.The second chapter presents the studies carried out in the context of the MINCE project. The first study is devoted to the chemical analysis of a sample of young giant stars that was serendipitously discovered during the first MINCE observations. My contribution in this work was to derive the stellar parameters, analyse the spectroscopic data, measure the rotational velocities, compare the results with theoretical models and write the paper. The second study presents the results obtained from the analysis of the first sample of MINCE stars. In this work, I contributed to the analysis of some of the stars in the sample.The third chapter presents the results obtained in the context of the CERES project. The first study presents a detailed chemical analysis of the star RAVE J110842.1-715300, with the aim of understanding whether or not it originated in the Omega Centauri globular cluster. My contribution in this study was to derive the stellar parameters of the star. The second study presents the results obtained for the CERES star sample. My contribution was to derive the parameters, compute model atmospheres, measure the chemical abundances, and write the paper.The fourth chapter presents the results obtained in the context of the High-speed stars project. The first study reports the results obtained from the high-resolution follow-up of two young and metal-poor stars in the sample of Caffau et al. (2020), to check whether they are blue stragglers or not. My contribution in this study was to obtain the high-resolution observations with UVES and to analyse the data. These results have not been published yet. The second study presents a detailed analysis of two high-speed stars observed with Subaru. In this study I was involved in the C abundance determination.The fifth chapter presents the results obtained from the chemical analysis of samples of stars selected using the Pristine photometry. The first study presents the chemical analysis of a sample of metal-poor stars that may have been enriched by the explosion of pair instability supernovae. My contribution was to select promising candidates and observe them with the SOPHIE spectrographat Observatoire de le Haute Provence (OHP)in visitor mode. The second study presents the preliminary results obtained from the chemical analysis of a sample of Pristine extremely metal-poor candidates. My contribution in this study was to derive the stellar parameters and the chemical abundances. The paper is in preparation.The sixth chapter concludes the thesis and gathers final reflections and future projects
Polles, Fiorella Lucia. "Properties of the interstellar medium of the star-forming galaxy, IC10, at various spatial scales". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS276/document.
Pełny tekst źródłaThe properties of the Interstellar Medium (ISM) strongly influence the environment and processes that lead to star-formation, which in turn, drives the evolution of a galaxy. Dwarf galaxies in the Local Group are perfect laboratories to investigate how the metal-poor ISM affects the interplay between gas, dust and stars. In this thesis, I investigate the properties of the HII regions and the diffuse ionized gas of the nearby dwarf galaxy IC10, which has a metallicity of 1/3 solar. Its proximity (d=700 kpc) enables the analysis on different spatial scales: from the compact clumps (~25 pc) to the whole star-forming body of the galaxy (~650pc). In order to measure the physical properties of the ISM, I model the infrared emission lines observed with Spitzer and Herschel with photoionization and photodissociation models. I present an extensive exploration of different methods to determine the most reliable ISM properties, based on the available constraints. I determined the properties of the brightest star-forming clumps within the galaxy and show that the emission at large scales (~300 pc) is dominated by that of the compact, bright clumps that lie within the region. I further demonstrate the need for a multi-component model to fully reproduce the observations
Delfosse, Xavier. "Naines brunes et étoiles de très faible masse". Phd thesis, Université Joseph Fourier (Grenoble), 1997. http://tel.archives-ouvertes.fr/tel-00686419.
Pełny tekst źródłaDelfosse, Xavier. "Naines brunes et étoiles de très faible masse". Phd thesis, Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10189.
Pełny tekst źródłaGallet, Florian. "Modélisation de l'évolution du moment cinétique des étoiles de faible masse". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY055/document.
Pełny tekst źródłaIn 1972, Skumanich discovers a unique empirical relationship between the rotation period of the surface of G star and their age on the main sequence. This discovery then opened a new path for stellar dating: the gyrochronology. Therefore, many authors in the late 80's and the begenning 90's, were interested in the evolution of the surface angular velocity of low-mass stars ($M_*$ = 0.4 $M_{odot}$- 1.1 $M_{odot}$). The first phenomenological models on the subject were born.The angular velocity evolution of these stars begins to be reasonably well reproduced by the class of parametrical model that I present in this thesis. Because of the lack of adequate theoretical descriptions, only the overall effects of the physical mechanisms involved are described here. The main issue is to study the framework and how the stellar angular momentum is affected by these processes and to constrain their main characteristics.Over the course of my thesis, I modelled the rotational tracks of external and median envelopes and median of rotation period distributions of 18 stellar clusters between 1 Myr and 1 Gyr. This allowed me to analyse the time dependence of the physical mechanisms involved in the angular momentum evolution of solar-type stars. The results I obtained show that the evolution of the internal differential rotation significantly impact the rotational convergence (empirical Skumanich's relationship), the evolution of the surface lithium abundance, and the intensity of the magnetic field generated by dynamo effect. In addition to the reproduction of these external envelopes, the model I developed provides constraints on the mechanisms of internal redistribution of angular momentum and the lifetimes of circumstellar disks, that are held responsible for the rotational regulation observed during the first few million years of pre-main sequence. The extension of the model to less massive stars (0.5 et 0.8 $M_{odot}$) that I performed also provided the mass dependence of these physical processes. Most specifically, this step added strong constraints on the characteristic time associated to the transport of angular momentum between the core and the envelope, on the efficiency of magnetic braking likely related to a change of topology from solar-type stars to those of 0.5 $M_{odot}$, and on the internal and external rotational history of stars from 1 Myr to 1 Gyr
Maret, Sébastien. "Structure physico-chimique des proto-étoiles de faible masse". Phd thesis, Université Paul Sabatier - Toulouse III, 2003. http://tel.archives-ouvertes.fr/tel-00003798.
Pełny tekst źródłaPhan, Bao Ngoc. "Étoiles de très faible masse dans le voisinage solaire". Paris 6, 2002. http://www.theses.fr/2002PA066459.
Pełny tekst źródłaAmard, Louis. "Évolution de la rotation des étoiles jeunes de faible masse". Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT258/document.
Pełny tekst źródłaThe angular momentum content of a star, as its mass or its chemical composition is one of the fundamental properties of a star, one of those that evolves with time and modify the stellar structure. The angular momentum can be studied as a global property, we can then observe it through the surface rotation velocity, or a local property that vary inside the star, we therefore have to probe the stellar radiation zone and study the secular angular momentum redistribution processes that happen in this region. During this PhD, in the frame of the ToUpiES project, we have been especially interested in the evolution of the young low-mass stars angular momentum, since this phase of evolution is critical regarding the evolution of extraction and redistribution angular momentum processes. First, we included in the STAREVOL evolution code the most up-to-date prescription for the wind-driven angular momentum extraction. We led a systematic study of the various combination of this braking with the different existing prescriptions for the treatment of horizontal and vertical turbulent motions in stellar radiative zones. This allows us to select a set of prescription able to reproduce the observed rotation periods in young open clusters for a broad mass-range. Next, we analysed how these prescriptions for extraction and transport of angular momentum behave when applied to a 1.2M⊙ model. We compared the result to what is obtained with other processes estimated as potentially very efficient to redistribute angular momentum (internal gravity waves, MHD Tayler-Spruit instability, gravity modes). This allows us to derive in each case, the specificity of the rotation profiles predicted by the different transport processes. Then, we set up a functional rotational model adapted to almost the entire range low-mass stars, allowing to reproduce the observed low-mass stars rotation periods in young open clusters (with 0, 2M⊙ ≤M≤ 1, 1M⊙). This models can also predict the rotational evolution at different metallicities. Eventually, these models have been used in the frame of various works in different domains such as the characterisation of planet host-stars, the evolution of the magnetic topology during the young stellar phases or even the impact of stellar evolution on the habitability of a planetary system
Lachaume, Régis. "Structure des disques d'accrétion autour des étoiles jeunes de faible masse". Phd thesis, Université Joseph Fourier (Grenoble), 2003. http://tel.archives-ouvertes.fr/tel-00006474.
Pełny tekst źródłaJe présente une étude de ces disques fondée sur une description analytique poussée du transfert radiatif, afin de retarder l'étape de mise en oeuvre numérique. Cette méthode possède l'avantage de permettre une meilleure compréhension des processus et des conditions physiques dans ces objets. Afin de contraindre les paramètres du modèle, j'ai choisi d'établir un diagnostic observationnel novateur sur la base de la distribution spectrale d'énergie, technique bien connue, et des visibilités obtenues en interférométrie optique à longue base, récentes et prometteuses car elles permettent d'obtenir des informations spatiales à l'échelle de l'unité astronomique pour les étoiles jeunes les plus proches.
Je commence par une généralisation des approches analytiques du transfert dans les atmosphères stellaires, en reliant la température en tout point à la profondeur optique, avec deux différences notables : le chauffage visqueux a lieu sur l'ensemble du disque et la surface est éclairée par l'étoile. Ce formalisme est ensuite employé dans une simulation numérique de disque chauffé par la viscosité seule. Ensuite, j'élabore une version simplifiée du transfert dans un disque à deux couches : une surface chauffée par la couche interne et par l'étoile, et un intérieur chauffé par la viscosité et par la couche externe. Cette version permet d'obtenir des formules analytiques simplifiées décrivant les conditions physiques dans un disque présentant les deux sources de chauffage énoncées.
Enfin, je m'attèle à l'interprétation des observations. Après une étude prospective concernant les possibilités ouvertes par l'interférométrie pour les objets marginalement résolus, je présente des ajustements du modèle à deux couches aux étoiles jeunes de faible masse déjà observées en interférométrie.
Boulard, Marie-Hélène. "Contribution à l'étude des milieux circumstellaires. Caractérisation des excès infrarouges pour les sources IRAS possédant une contrepartie visible. Etude d'objets jeunes de faible masse". Toulouse 3, 1995. http://www.theses.fr/1995TOU30012.
Pełny tekst źródłaBenbakoura, Mansour. "Evolution des étoiles de faible masse en interaction : observations multi-techniques et modélisation des systèmes multiples". Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7027.
Pełny tekst źródłaThis thesis is devoted to the study of low-mass stars having other stars or planets in their immediate environment. We focused on the influence of interactions with these companions on stellar evolution and their observable consequences.In the first part, we present the model of evolution of star–planet systems that we developed during this thesis, called ESPEM (French acronym for Evolution of Planetary Systems and Magnetism). This model incorporates ab-initio prescriptions to quantify the effects of magnetized stellar wind and tidal dissipation on stellar rotation and planetary orbit, simultaneously with the star's structural evolution. First, we use it to study the secular evolution of the rotation of planet-host stars and show that this evolution can be significantly different from that of isolated stars. Next, we examine the predictions of this model regarding the orbital architecture of star–planet systems. Our results suggest an interpretation to the observed distributions of orbital and stellar rotation periods.In the second part of the manuscript, we show how the observation of advanced binary stars allows us to test astrophysical theories, in particular asteroseismology and tidal interaction. First, we present the results of an observation program that we conducted for more than two years and that allowed us to characterize 16 eclipsing binary systems. Then, we compare these results with those obtained by analyzing this sample using asteroseismic tools to verify the accuracy of the latter. Finally, by extending the studied sample to 30 other advanced binary stars including an evolved primary, we test the theory of tidal evolution. This allows us both to validate the theory and to understand the evolution of the systems observed in this work.This work highlights two aspects of the specificity of multiple systems. First, it shows how the evolution of stars is affected by the presence of a stellar or planetary companion. Second, it emphasizes the interest of binary stars in testing astrophysical theories and reinforces the current understanding of stellar evolution
Allain, Stéphanie. "L'évolution du moment cinétique des étoiles pré-séquence principale de faible masse". Grenoble 1, 1997. http://www.theses.fr/1997GRE10167.
Pełny tekst źródłaBoirin, Laurence. "Etude de la variabilité des binaires X de faible masse à partir d'observations avec RXTE". Toulouse 3, 2001. http://www.theses.fr/2001TOU30025.
Pełny tekst źródłaMorin, Julien. "Processus dynamos dans les étoiles entièrement convectives". Phd thesis, Université Paul Sabatier - Toulouse III, 2009. http://tel.archives-ouvertes.fr/tel-00480428.
Pełny tekst źródłaCabrit, Sylvie. "Ejection de matière dans les objets protostellaires et les étoiles jeunes de faible masse". Phd thesis, Université Pierre et Marie Curie - Paris VI, 1989. http://tel.archives-ouvertes.fr/tel-00725199.
Pełny tekst źródłaYvart, Walter. "Signatures moléculaires dans les vents de disque MHD des proto-étoiles de faible masse". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00880647.
Pełny tekst źródłaSégransan, Damien. "Les étoiles de très faible masse du voisinage solaire : multiplicité et relation masse-luminosité". Université Joseph Fourier (Grenoble), 2001. http://www.theses.fr/2001GRE10082.
Pełny tekst źródłaBonne, Lars. "La formation du gaz dense à l'origine des étoiles de faible et de haute masse". Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0121.
Pełny tekst źródłaTo understand how stars can form in the interstellar medium (ISM), it has to be understood how cold (~ 10 K) and dense gas (> 10^{4} cm^{-3}) can emerge during the evolution of the ISM. With the Herschel telescope it was found that most of this dense star forming gas is organised in filamentary structures.To understand how this dense filamentary gas forms, multiple CO transitions were observed towards the Musca filament, which can form low-mass stars, using the APEX telescope. These observations were complemented with [CII] and [OI] observations by the SOFIA telescope. The non-detection of [CII] demonstrates that the Musca cloud is embedded in a weak FUV field (< 1 G0). However, the observed CO(4-3) line with APEX demonstrates the presence of warm (> 50 K) CO gas around the Musca filament which cannot be explained with heating by the FUV radiation field. A comparison of the observed CO(4-3) emission with shock models shows that the emission can be the result of a low-velocity (< 4 km/s) J-type shock. Further analysis of this emission demonstrates that this shock emission resembles the signature of a shock responsible for mass accretion on a filament. This suggests that a low-velocity shock as a result of continuous mass accretion is responsible for the formation of cold and dense gas that can form stars in the Musca filament.The accretion scenario for Musca is further analysed with low-J CO observations from APEX and NANTEN2 to study the large scale gas kinematics. These observations unveil a velocity gradient over the Musca filament crest which is correlated with the velocity field of the nearby ambient gas. This suggests that the velocity gradient is the result of mass accretion from the ambient cloud. Analysing the full Musca cloud demonstrates a spatial and kinematic asymmetry from low- to high-density gas. This asymmetry is seen as a V-shape in the position-velocity (PV) diagram perpendicular to the Musca filament. Including atomic hydrogen (HI) observations in the analysis first of all confirms that Musca is part of a larger HI cloud, the Chamaeleon-Musca complex. It also demontrates that the kinematic asymmetry is seen from the HI cloud down to the filament crest. Furthermore, the CO-HI asymmetry is found for basically all dense regions (Cha I, Cha II, Cha III and Musca) with archival data of Chamaeleon-Musca, while HI shows indications of more than one velocity component. This asymmetric accretion scenario is predicted by magnetised cloud-cloud collision simulations, where the bending of the magnetic field is responsible the observed asymmetric accretion scenario. The filament formation in Musca is thus the result of two intersecting converging flows which are driven by the magnetic field bending due to a large-scale colliding HI flow that triggered the observed star formation in the full Chamaeleon-Musca complex.Finally, the kinematics of the high-mass star forming ridge DR21 and its surrounding gas are studied to compare low- and high-mass star formation. This shows a similar spatial and kinematic asymmetry as in Musca, which suggests that DR21 is formed by a giant molecular cloud (GMC) collision. However, it is also found for high-mass star formation in the DR21 cloud that gravity plays an important role on large scales (> 1 pc) while for Musca gravity only starts to dominate locally (r < 0.1-0.2 pc). So, due to the high density in the DR21 cloud after the GMC collision, gravity eventually drives the evolution of the compressed cloud for high-mass star forming regions. Kinematic observations of the full Cygnus-X north region show further indications of two interacting velocity components over the entire region, which indicates that a high-velocity (> 10 km/s) GMC collision can result in the formation of an OB association similar to OB2. These OB stars then form in gravitationally collapsing hubs and ridges due to the compression by the GMC collision
Astoul, Aurélie. "Impact du magnétisme et de la rotation différentielle sur les marées dans les étoiles de faible masse et les planètes géantes gazeuses". Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7073.
Pełny tekst źródłaMore than 4000 exoplanets have been discovered in the last 25 years, most of them around low-massstars. In close planetary systems, star-planet tidal interactions are known to govern the late evolution of the systems’ orbital architecture and the rotation of their host star, as is also the case in the tight planet-satellite systems of our solar system such as the Jovian and Saturnian systems. The characteristic times of variation of orbital parameters and bodies’ rotation are dictated by the magnitude of tidal dissipation, which varies considerably with the mass, rotation and metallicity of stars and with the structure and internal dynamics of stars and planets.In order to model and realistically characterise the tidal dissipation in the convective envelopes of these astrophysical objects, two key physical mechanisms are studied in this thesis : differential rotation and magnetism, through their influence on tidal flows in convective regions. These two aspects are explored using semi-analytical and numerical approaches, while applying our results inside stars during their evolution, and gas giant planets such as Jupiter and Saturn.First of all, we have been interested in the impact of magnetism on the excitation and dissipation of tidal magneto-inertial waves along the evolution of low-mass stars of spectral type M to F, by examining the limits of their convective envelope, i.e. the interface between the radiative and convective zones and the regions close to their surface. To do so, we have used in synergy tidal wave physics, the scaling laws from dynamo theory that allow us to estimate the amplitude of a large-scale magnetic field, and the grids of numerical models of stellar evolution taking into account rotation. We thus show that the contribution of magnetism on tidal forcing, i.e. on wave excitation, remains negligible compared to the hydrodynamic contribution classically used, whatever the position in the convective envelope, the mass, or the age of the studied low mass star. On the other hand, the Ohmic dissipation mechanism of magneto-inertial waves is a very efficient mechanism, even preponderant in front of the viscous dissipation, for M to F type stars, from the pre-main sequence to the end of the main sequence, in all their convective envelope. These results also apply in the case of Jupiter and its Galilean satellites.In parallel to this work, we have developed a local shear-box model, inclined with respect to the axis ofrotation of the studied body, in order to understand the complex interaction between tidal inertial waves and zonal flows in the vicinity of critical layers, and in particular at the corotation resonance, which are regions where the tidal wave frequency vanishes or is commensurable with the local rotation frequency of the considered body. This model has allowed us to study the impact of different realistic rotation profiles, such as those observed in solar-type stars, or in giant planets such as Jupiter and Saturn. Thanks to this work, we have identified different transmission regimes of the wave energy flux, for which the wave can, in the vicinity of a critical layer, either deposit energy and be damped, or extract energy from the mean flow and thus be amplified. These different transmission regimes exist for each of the examined conical and cylindrical rotational profiles, and depend on the critical level encountered, the wave properties and the mean flow profile
Masson, Jacques. "Etude des effets de la magnétohydrodynamique non idéale sur la formation des étoiles de faible masse". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00942777.
Pełny tekst źródłaParise, Bérangère. "La deutération dans les protoétoiles de faible masse". Toulouse 3, 2004. https://tel.archives-ouvertes.fr/tel-00009303.
Pełny tekst źródłaDespite the low deuterium abundance in the Universe (D/H ~ 1. 5x10-5), high abundances of deuterated molecules are detected in star forming regions, with a fractionation higher than the cosmic abundance of deuterium by several orders of magnitude. We study in this thesis the physical and chemical processes leading to the high molecular deuteration observed in low-mass protostellar environments. We present observations of deuterated molecules (namely methanol, formaldehyde and water) both in the gas and in the icy mantles of dust grains in the envelope surrounding such objects. Millimeter observations unveiled a high deuteration of methanol in the gas of the envelope. In particular, triply-deuterated methanol was detected with a fractionation CD3OH/CH3OH ~ 1% in IRAS16293-2422. The observed fractionations are consistent with the scenario of formation of methanol on dust grain surfaces. Deuterated methanol and formaldehyde were then searched for and detected on a sample of low-mass Class 0 protostars, suggesting that this high deuteration is common in this class of objects. Analysis of the gas-phase water emission in the IRAS16293-2422 envelope leads paradoxically to a fractionation one order of magnitude lower, in agreement with the upper limit on water deuteration in ices, derived by near-infrared observations towards slightly more evolved objects. The last chapter of the thesis presents a grain chemistry model that studies in details water fractionation
Guenel, Mathieu. "Dissipation de marée dans les étoiles de faible masse et les planètes géantes : ondes inertielles, structure interne et rotation différentielle". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS307/document.
Pełny tekst źródłaThis thesis studies the tidal dissipation mechanisms in low-mass stars that have an external convective envelope like the Sun (i.e. from M- to F-type stars), as well as in Jupiter- and Saturn-like gaseous giant planets. We particularly focus on understanding and characterizing the influence of the internal structure and dynamics of these bodies on the various physical mechanisms that cause this tidal dissipation, in order to assess their relative strength.In the case of giant planets, we use preexisting semi-analytical models and we show that the dissipation induced by the possible presence of a viscoelastic solid core is not negligible compared to the one induced by inertial waves (whose restoring force is the Coriolis acceleration) in the convective envelope. For low-mass stars, we perform a new semi-analytic study as well as numerical simulations of tidal inertial waves propagating in the external convective envelope, and we compute the associated energy dissipation. For the first time, the effects of a background latitudinal differential rotation, as observed in the Sun and predicted by various numerical simulations of convection in low-mass stars, is taken into account. We highlight the existence of new families of inertial modes as well as the importance of corotation resonances for tidal dissipation. Finally, we derive a new prescription for the turbulent viscosity applied to these tidal waves that takes into account the influence of rotation on the properties of convective flows along the evolution of stars
Nguyen, Phuong. "Formation des planètes observée avec ALMA : propriétés du gaz et de la poussière des disques protoplanétaires orbitant autour des étoiles jeunes de faible masse". Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0249.
Pełny tekst źródłaThis thesis presents the analysis of the gas and dust properties of the protoplanetary disk surrounding the young low-mass (∼ 1.2 M⊙) triple star GG Tau A. Studying such young multiple stars is mandatory to understand how planets can form and survive in such systems shaped by gravitational disturbances. Gravitational interactions linked to the stellar multiplicity create a large cavity around the stars, the matter (gas and dust) being either orbiting around the stars (inner disks) or beyond the cavity (outer disk). In between, the matter is streaming from the outer disk onto the inner disks to feed up the central stars (and possible planets).This work makes use of millimeter/sub-millimeter observations of rotational lines of CO (12CO, 13CO and C18O) together with dust continuum maps. While the 12CO emission gives information on the molecular layer close to the disk atmosphere, its less abundant isotopologues (13CO and C18O) bring information much deeper in the molecular layer. The dust mm emission samples the dust disk around the mid-plane.After introducing the subject, I present the analysis of the morphology of the dust and gas disk. The disk kinematics is derived from the CO analysis. I also present a radiative transfer model of the ring in CO. The subtraction of this model from the original data reveals the weak emission of the molecular gas lying inside the cavity. Thus, I am able to evaluate the properties of the gas inside the cavity, such as the gas dynamics and excitation conditions and the amount of mass in the cavity. The outer disk is in Keplerian rotation until the inner edge of the dense ring at ∼ 160 au. The disk is relatively cold with a CO gas temperature of 25 K and a dust temperature of ∼14 K at 200 au from the central stars. Both CO gas and dust temperatures drop very fast (∝ r−1). The gas dynamics inside the cavity is dominated by Keplerian rotation motion. The contribution of infall motion is evaluated at ∼ 10 − 15% of the Keplerian velocity. The gas temperature inside the cav- ity is of the order of 40 − 80 K. The CO column density and H2 density along the “streamers”, which are close to the binary components (around 0.3′′ − 0.5′′) are of the order of a few 1017 cm−2 and 107 cm−3, respectively. The total mass of gas inside the cavity is ∼ 1.6 × 10−4 M⊙ and the accretion rate is estimated at the level of 6.4 × 10−8 M⊙ yr−1. These new results provide the first quantitative global picture of the physical properties of a protoplanetary disk orbiting around a young low-mass multiple star able to create planets.I also discuss some chemical properties of the GG Tau A disk. I report the first detection of H2S in a protoplanetary disk, and the detections of DCO+, HCO+ and H13CO+ in the disk of GG Tau A. Our analysis of the observations and its chemical modeling suggest that our understanding of the S chemistry is still incomplete. In GG Tau A, the detection of H2S has been likely possible because the disk is more massive (a factor ∼ 3 − 5) than other disks where H2S was searched. Such a large disk mass makes the system suitable to detect rare molecules and to study cold- chemistry in protoplanetary disks
Chủ đề nghiên cứu của luận án là về tính chất của khí và bụi trên đĩa tiền hành tinhquanh một hệ đa sao có khối lượng ∼1.2 Msun, GG Tau A. Nghiên cứu các hệ đa saotrẻ là cần thiết để hiểu về sự hình thành và tồn tại của hệ hành tinh trong môi trườngnhiễu loạn hấp dẫn. Tương tác hấp dẫn của hệ đa sao tạo nên một khoang rỗng lớnxung quanh các sao thành phần, vật chất (khí và bụi) của hệ có thể quay quanh từngsao đơn ("đĩa trong") và bên ngoài khoang rỗng, xung quanh cả hệ sao ("đĩa ngoài").Ở giữa hai phần này của hệ, vật chất được truyền từ đĩa ngoài vào đĩa trong để nuôidưỡng các sao ở trung tâm (hoặc có thể cả hành tinh).Nghiên cứu của luận án sử dụng các quan sát thiên văn vô tuyến ở bướcsóng millimet/dưới-millimet phát ra bởi các phân tử CO (12CO, 13CO và C18O) và bụi.Phát xạ từ 12CO cung cấp thông tin về lớp phân tử gần với khí quyển của đĩa, cácđồng phân kém phổ biến hơn (13CO và C18O) cung cấp thông tin nằm sâu hơn tronglớp phân tử của đĩa. Phát xạ mm của bụi giúp nghiên cứu các tính chất trên mặtphẳng giữa của đĩa.Sau khi giới thiệu về chủ đề và đối tượng nghiên cứu, tôi trình bày về hình tháivà động học của đĩa khí và bụi của hệ sao. Tôi cũng trình bày mô hình truyền bức xạcủa đĩa ngoài sử dụng các đồng phân của CO. Đĩa ngoài của hệ tuân theo chuyểnđộng Kepler cho đến gần khoang rỗng, ∼160 au từ tâm sao, và tương đối lạnh. Nhiệtđộ khí CO và bụi lần lượt là 25K và 14K tại khoảng cách 200au, và giảm nhanh khikhoảng cách tới tâm tăng, T ∝ r−1. Việc trừ mô hình đĩa ngoài từ số liệu ban đầu biểulộ rõ ràng hơn phát xạ yếu của các phân tử khí trong khoang rỗng. Do đó, động họcvà điều kiện phát xạ của khí trong khoang rỗng có thể được đánh giá. Các phân tửkhí bên trong khoang rỗng bị chi phối bởi chuyển động quay, với sự đóng góp nhỏcủa chuyển động rơi được đánh giá vào cỡ 10–15% chuyển động Kepler. Nhiệt độkhí bên trong khoang rỗng trong khoảng 40–80 K, mật độ dài của khí CO và mật độkhối của H2 lần lượt là 1017cm−2 và 107cm−3. Tổng khối lượng khí trong khoang rỗnglà ∼1.6×10−4 Msun, tốc độ truyền vật chất từ đĩa ngoài vào đĩa trong được tính vàokhoảng ∼ 6.4×10−8 Msun yr−1. Các kết quả nghiên cứu này góp phần cung cấp mộtbức tranh tổng quát định lượng đầu tiên về tính chất vật lý của đĩa tiền hành tinhquay xung quanh một hệ đa sao trẻ có khối lượng thấp, nơi có khả năng hình thànhhành tinh.Một vài tính chất hóa học của đĩa tiền hành tinh GG Tau A cũng được nghiêncứu trong luận án này. Tôi trình bày về sự phát hiện lần đầu tiên H2S trong đĩa tiềnhành tinh, cũng như sự phát hiện lần đầu tiên DCO+, HCO+ và H13CO+ trong đĩa GGTau A. Kết quả phân tích số liệu thực nghiệm và mô hình hóa học cho thấy sự hiểubiết của chúng ta về hóa học các phân tử có chứa sulfur trong đĩa là chưa hoànthiện. Trong đĩa tiền hành tinh GG Tau A, khả năng phát hiện được phân tử hiếmnhư H2S có thể là nhờ vào khối lượng lớn của đĩa (lớn hơn khoảng 3–5 lần so vớicác đĩa tiền hành tinh nơi H2S đã từng được tìm kiếm). GG Tau A với đĩa tiền hànhtinh có khối lượng lớn là thích hợp để tìm kiếm các phân tử hiếm và nghiên cứu vềthành phần hóa học của đĩa có nhiệt độ thấp
Montalban, Iglesias Josefa. "Mélange de matière à l'intérieur radiatif des étoiles de faible masse induit par ondes de gravité : application aux abondances des éléments légers et au flux de neutrinos solaires". Paris 7, 1995. http://www.theses.fr/1995PA077059.
Pełny tekst źródłaBoutelier, Martin. "Etude des Oscillations Quasi Périodiques dans les systèmes binaires X de faible masse". Phd thesis, Université Paul Sabatier - Toulouse III, 2009. http://tel.archives-ouvertes.fr/tel-00444379.
Pełny tekst źródłaBardeau, Sébastien. "Distribution de masse d'un échantillon d'amas de galaxies déterminée par effet de lentille gravitationnelle faible". Toulouse 3, 2004. https://tel.archives-ouvertes.fr/tel-00008027.
Pełny tekst źródłaOne of the strongest predictions of Einstein's General Relativity is the ability of any mass to curve space-time and consequently to deflect light rays. One of its direct consequence is then the gravitational lensing effect: images of sources located in the background of a massive object lying on the line-of-sight are distorted, magnified or even splitted in multiple images. Galaxy clusters, the most massive structures in the Universe, are able to generate the strongest effect. The history, the formation process and the dynamical state of these entities are clues to understand the formation and the evolution of the Universe itself. This thesis aims at understanding and constraining the mass distribution of a sample of galaxy clusters measured from weak gravitational lensing, thanks to a statiscal study of weakly distorted objects
Guérou, Adrien. "Formation et évolution des galaxies de faible masse, de l'univers local aux décalages spectraux intermédiaires". Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30256.
Pełny tekst źródłaLow-mass galaxies form the most numerous galaxy population in the Universe at all cosmic times, and are legitimately considered as the "building-blocks" of galaxy formation in a cosmological context. In the local Universe, low-mass galaxies are preferentially found in galaxy clusters where they form through a complex chain of in-situ formation and accretion events. However, the detailed formation and evolution processes of low-mass galaxies, and their exact roles in the formation of more massive galaxies are still poorly constrained, in particular due to challenging observations. After setting the scene with an introduction on our current understanding of low-mass galaxies, I present the study of a sample of eight compact low-mass galaxies in the Virgo cluster. I derive their stellar kinematics as well as the age and metallicity of their stellar content from GMOS/Gemini Integral Field Spectrograph (IFS) data, and demonstrate that the stellar population properties evolve smoothly with galaxy size, mass and environment over the full range of galaxy mass. This suggests that a similar set of physical processes is at play on both low- and high-mass galaxies, but the relative efficiency of each of these processes in shaping galaxies varies smoothly from the low- to the high-mass ends. I then derive their star formation histories as well as those of a sample of 20 more extended typical low-mass galaxies, and present a study of their dependencies on the environment and the mass of their host galaxy. As a result, I underline through this work that the environment as well as the most massive galaxies play an important role in controlling the formation and evolution of low-mass galaxies. But local galaxies only represent the end products of a complex evolution path, leaving ambiguity about the early evolution of galaxies. However, I then show with the help of IFS observations of the nearby galaxy NGC3115 obtained with MUSE/VLT, that two-dimensional maps of the kinematics and stellar populations of galaxies, with large spatial coverage and high spatial resolution, are keys to unveil their whole mass assembly history, and thus their formation and evolution through all cosmic times. Thus, to better constrain the evolution of low-mass galaxies, I use deep MUSE/VLT observations in the Hubble Deep Field South to study low-mass galaxies at intermediate redshift. I derive for the first time the spatially resolved stellar kinematics of a sample of ten galaxies at a redshift between z ~ 0.2 - 0.7, and show that the stellar rotation amplitude and velocity dispersion are in agreement with previous studies of their gas kinematics. Such information put into the light of current galaxy evolution models will help to better understand the growth of stellar mass in galaxies and the origins of today low-mass galaxies
Dassa-Terrier, Julien. "Andromède : à propos de la faible densité du gaz moléculaire et de la formation d'étoiles dans sa région circum-nucléaire". Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEO001.
Pełny tekst źródłaThe galaxy M31 shows an atypical morphology for a spiral galaxy, with its two rings struc- ture (the eccentric 1 kpc inner ring and the outer 10 kpc ring) which contains most of the gaz mass of the galaxy. Its circum-nuclear region is especially empty and star formation seems absent, leading us to expect Andromeda’s nucleus gaz reservoir to be depleted. Explanations for this phenomenon are still up for debate. The main hypothesis include stellar feedback triggered by a recent starburst, gaz infall in the black hole or a head-on collision with M32 which could have redistributed the gaz in M31 rings. In this thesis, we use interferometric data to explore the gaz density within the central 165 pc of M31. We produce a 12 molecular clouds catalog and rely on GALEX, SDSS, 2MASS and SPITZER data to study the spectral energy distribution. It showed to be consistent with a combination of SED models with a strong contribution of a 8 Gyr old stellar population and a modest contribution of 200 Myr old stellar population. The study of the PAH in the black hole sphere of influence is compatible with the existence of a recent starburst. We create a new SFR map for M31 nucleus. Our work confirms the low density of molecular gaz and star formation in the circum-nuclear region. We estimate the total gas mass (8.4 ± 0.4) × 10^4 M⊙ and set an upper limit for the surface density SFR 1.2 × 10^−3 M⊙yr^−1kpc^−2
Barret, Didier. "Modélisation de la réponse spectrale du télescope spatial SIGMA. Etude des propriétés spectrales des binaires X de faible masse dans la gamme d'énergie 35-500 keV : [thèse en partie soutenue sur un ensemble de travaux]". Toulouse 3, 1993. http://www.theses.fr/1993TOU30260.
Pełny tekst źródłaCoutens, Audrey. "La deutération de l'eau dans les régions de formation stellaire : Apport des données spectroscopiques Herschel/HIFI". Phd thesis, Université Paul Sabatier - Toulouse III, 2012. http://tel.archives-ouvertes.fr/tel-00763292.
Pełny tekst źródłaBolmont, Emeline. "Evolution et habitabilité de systèmes planétaires autour d’étoiles de faible masse et de naines brunes". Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14897/document.
Pełny tekst źródłaThe discovery of more than 900 planets orbiting other stars than our Sun makes this period very exciting. Our knowledge which was based on the Solar System has been challenged by new planetary systems which are very different from our system. Some of them are much more compact than the Solar System. Some planets are located extremely close-in from their star, within the orbital distance of Mercury, in a region where tidal effects are important. Understanding the structure of the known exoplanetary systems and the future ones requires to take into account the physics of tidal evolution.The missions dedicated to the finding of exoplanets are beginning to detect less massive planets in the habitable zone of their host star. The habitable zone is here defined as the range of orbital distances where a planet with an atmosphere can sustain liquid water at its surface. The study of the climate of exoplanets, given a stellar flux and spectra, is important for the characterization of planetary atmosphere – which JWST will make possible.This thesis provides a study of the dynamical and tidal evolution of planetary systems orbiting evolving brown dwarfs and low mass stars in order to constrain some tidal parameters and in the case of planets around brown dwarfs put some constrains on observability. First, I studied the tidal evolution of single-planet systems orbiting a brown dwarf, a M-dwarf or a Sun-like star whose radius evolution is taken into account. The aim of this study was to study the influence of the contraction of the brown dwarf or star on the orbital evolution of the planets. Second, I endeavored to study the tidal evolution of multiple-planet systems orbiting a brown dwarf, a M-dwarf or a Sun-like star whose radius evolution is also taken into account.These two projects allow me to study the question of the habitability of planets orbiting those objects, in particular orbiting brown dwarfs which are known to cool down with time. A planet orbiting a brown dwarf in its habitable zone is sufficiently close to the brown dwarf to feel tidal effects. So parameters such as the eccentricity or obliquity, which are important for the climate are partially determined by tides. In this thesis, this question is briefly addressed but will be deepened in a future post-doc
Bonnefoy, Mickaël. "Recherche et caractérisation des propriétés physiques et chimiques des compagnons de faible masse, naines brunes et planètes géantes, à l'aide d'observations à haut contraste et à haute résolution angulaire". Grenoble, 2010. http://www.theses.fr/2010GRENY035.
Pełny tekst źródłaMy work takes place in the dynamic context of the direct detection of low mass companions (brown dwarfs, extrasolar planets). I intent to characterize their physical and chemical properties, and to understand the mechanisms that lead to their formation and drive their evolution. This requires using high contrast and high angular resolution techniques in order to resolve the close environment of the stars without being limited by their flux. I had the opportunity to participate to observational campaigns so as to detect new sources. I developed a set of data analysis tools designed to extract the spectra and the flux of the objects into photometric bands. Finally, I used this information to study the physical (radius, mass, age) and the atmospheric (composition, effective temperature, surface gravity) properties of these objects. The first part of this manuscript focus on the detection of young (age < 100 Myrs) low mass companions using imaging. I describe a set of reduction and analysis tools dedicated to the angular differential imaging technique. These tools have been used on data coming from the NaCo instrument located on the Very Large Telescope (Chile). They allowed re-detecting the extrasolar planet β Pictoris b. This companion is closer to its star than any of the extrasolar planets detected directly so far. This discovery brings the definite proof that giant planets can form in less than 12 million years within disks. I finally present a complementary analysis I conducted to initiate the characterization of this valuable object. The determination of the spectroscopic properties of young and low mass objects in the near infrared (1. 1-2. 5 µm) constitutes the second aspect of my work (and is reported in the last part of the manuscript). I started developing analysis and processing tools dedicated to data gathered on the adaptive optics assisted integral field spectrograph SINFONI. These efforts were used to analyze the spectrum of the planet/brown dwarf companion AB Pic b. This work was pursued to built a spectral library of young objects. This library brings a collection of reference spectra, necessary for the study of other young companions. It also brings new constraints on the latest generation of atmospheric models of cool objects. To conclude, I used the instrument NaCo and SINFONI to characterize the binary system TWA 22AB that could calibrate evolutionary models of low mass objects
Galametz, Maud. "Toward the Comprehension of the Infrared to Submillimeter View of the Interstellar Medium of Nearby Galaxies". Phd thesis, Université Paris-Diderot - Paris VII, 2010. http://tel.archives-ouvertes.fr/tel-00555151.
Pełny tekst źródłaNeves, Vasco. "Étude sur les paramétres stellaires des naines M et leur lien à la formation planétaire". Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY082/document.
Pełny tekst źródłaAt the time of writing of this Thesis more than 900 planets have been announced and about 2700 planets from the Kepler space telescope are waiting to be confirmed. The very precise spectra and light curves obtained in Doppler and transit surveys, allows the in-depth study of the parameters of the host stars, and opens the possibility to investigate the star-plant correlations. Also, determining the stellar parameters with precision is critical for more precise determinations of the planetary parameters, namely, mass, radius, and density.In the case of the FGK dwarfs, the determination of stellar parameters is well established and can be used with confidence to study the star-planet relation as well as to obtain precise planetary parameters. However, this is not the case for M dwarfs, the most common stars in the Galaxy. Compared to their hotter cousins, M dwarfs are smaller, colder, and fainter, and therefore harder to study. The biggest challenge regarding M dwarfs is related to the presence of billions of molecular lines that depress the continuum making a classical spectral analysis almost impossible. Finding new and innovative ways to overcome this obstacle in order to obtain precise stellar parameters is the goal of this Thesis.To achieve this goal I focused my research into two main avenues: photometric and spectroscopic methods. My initial work had the objective of establishing a precise photometric metallicity calibration, but I could not reach this goal, as I did not have enough FGK+M binaries with good photometric data. However, it was possible, with the available data, to compare the already established photometric calibrations and slightly improve the best one, as described in Chapter 3.Then, I focused on spectroscopic approaches with the aim of obtaining precise M dwarf parame- ters. To this end I used HARPS high-resolution spectra and developed a method to measure the spectral lines disregarding the continuum completely. Using this method I established a new visible calibration with a precision of 0.08 dex for [Fe/H] and 80 K for Te f f . This work is detailed in Chapter 4.Finally, I also participated in the refinement of the parameters of the star GJ3470 and its planet, where my expertise in stellar parameters of M dwarfs had an important role. The details regarding this investigation are shown in Chapter 5
No momento em que escrevo esta Tese, o número de planetas anunciados já ultrapassou os 900 e os cerca de 2700 candidatos detectados pelo telescópio espacial Kepler esperam por confirmação. Os espectros e as curvas de luz obtidos nos programas de procura de planetas permitem, também, o estudo em profundidade dos parâmetros das estrelas com planetas e abrem a possibilidade de investigar a relação estrela-planeta. Neste contexto, a determinação com precisão dos parâmetros estelares é crítica na determinação precisa dos parâmetros planetários, nomeadamente, a massa, o raio e a densidade.No caso das anãs FGK, os métodos de determinação dos parâmetros estelares estão bem estabelecidos e podem ser usados com confiança no estudo da relação estrela-planeta, assim como na obtenção de parâmetros planetários precisos. No entanto, não é esse o caso para as anãs M, as estrelas mais comuns da nossa Galáxia. Ao contrário das suas primas, as estrelas M são mais pequenas, frias e ténues e, assim sendo, mais difíceis de estudar. O grande entrave no estudo das estrelas M está relacionado com a presença de biliões de linhas moleculares que deprimem o contínuo espectral, fazendo com que uma análise espectral clássica se torne quase impossível. A procura de métodos inovadores que possibilitem ultrapassar este obstáculo, tendo em vista a obtenção de parâmetros precisos, é o objectivo desta Tese.Tendo em conta esse objetivo, foquei os meus esforços em duas linhas principais de pesquisa, baseadas em métodos fotométricos e métodos espectroscópicos. O meu trabalho inicial tinha como objetivo o estabelecimento de uma calibração fotométrica para a metalicidade, mas não me foi possível atingir esse objetivo, pois não tinha sistemas binários FGK+M suficientes com bons dados fotométricos. No entanto, foi possível, com os dados disponíveis, comparar as calibrações fotométricas existentes e refinar ligeiramente a melhor delas, como descrito no Capítulo 3.Após este trabalho passei a concentrar-me em técnicas espectroscópicas de obtenção de parâmetros estelares em estrelas M. Tendo em mente esse objetivo, usei espectros HARPS de alta resolução para desenvolver um novo método de medição de linhas espectrais independente do contínuo espectral. Seguidamente, usei este método no desenvolvimento de uma nova calibração de metalicidade e temperatura efectiva em estrelas M na região do visível, através da qual consegui atingir uma precisão de 0.08 dex para a [Fe/H] e de 80 K para a temperatura. Este trabalho está descrito no Capítulo 4.Ao mesmo tempo colaborei na determinação com precisão dos parâmetros da estrela GJ3470 e do seu planeta, onde a minha proficiência na determinação de parâmetros estelares em anãs M teve um papel importante. Os detalhes relacionados com este trabalho de investigação estão descritos no Capítulo 5
Morey, Etienne. "Purge, excitation dynamique et structuration des disques de débris soumis à l'interaction gravitationnelle de planètes et d'étoiles voisines". Phd thesis, Observatoire de Paris, 2013. http://tel.archives-ouvertes.fr/tel-00917968.
Pełny tekst źródłaMorey, Etienne. "Purge, excitation dynamique et structuration des disques de débris soumis à l'interaction gravitationnelle de planètes et d'étoiles voisines". Phd thesis, Observatoire de Paris (1667-....), 2013. http://www.theses.fr/2013OBSP0235.
Pełny tekst źródłaA debris disk around a main sequence star is made of planetesimals, which are the remnant of the planet formation process according to the core-accretion theory. In the Solar system, the main asteroid belt and the Kuiper belt are examples of debris disks. Around other stars, debris disks are observable if they are massive enough for collisions between planetesimals to produce continuously enough dust to be detected, by their thermal emission in the far infrared, or by scattered light in the visible spectrum. In this work, we have studied the stripping, the dynamical excitation and the structuring of debris disksundergoing the gravitational interaction with a planet inside a system, a stellar companion in a binary system, and a passing star in the dense environment of an open cluster during the first 100 millions years after the birth of the star. We have addressed these problems by the numerical simulation of the dynamics of a disk of planetesimals in these various conditions. We have finally carried out a study to determine the characteristics of the debris disk population around stars of different types, with the standard collisional evolution model, our results about dynamical excitation of disks and the data of the Spitzer surveys. We show that the lack of debris disks detected around low mass M type stars can be explained by planetesimals 10 times smaller than around solar type or more massive stars
Joos, Marc. "Effondrement et fragmentation des cœurs denses préstellaires : Étude de la formation des disques protostellaires". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00766166.
Pełny tekst źródłaGendre, Bruce. "Etude des sources X faibles des amas globulaires de la galaxie avec XMM-Newton". Phd thesis, Université Paul Sabatier - Toulouse III, 2004. http://tel.archives-ouvertes.fr/tel-01025786.
Pełny tekst źródłaBottinelli, Sandrine. "Hot corinos : molécules pré-biotiques autour des protoétoiles de type solaire". Grenoble 1, 2006. http://www.theses.fr/2006GRE10127.
Pełny tekst źródłaOne of the major goals of modern astrophysics is to understand the formation of our Solar System. Since low-mass protostars are suns in the making, the study of these objects and their environment provides one of the best ways to investigate the Sun's formation process and to peek in the past history of our Solar System. In my thesis, I focused on the chemistry occuring in Class 0 sources (the earliest known phases in the evolutionary scenario of low-mass protostars) by studying complex organic molecules in their envelopes. Such molecules have been discovered in IRAS16293--2422, the prototype of Class 0 sources, proving the existence of hot corinos, the inner regions of the protostellar envelope where the icy grain mantles sublimate. Some of these molecules have also been observed in comets in our Solar System, raising the question of whether (and if so, how) the chemistry of Class 0 objects affects the chemical composition of the protoplanetary disk material from which comets and other planetary bodies form. However, it is first necessary to determine whether hot corinos are ubiquitous in low-mass protostars or if IRAS16293-2422 is an exception. This was the first goal of my thesis. The approach consisted mainly in observing three Class 0 sources to search for complex organic molecules. I thereby discovered and/or confirmed three more hot corinos. The second goal was then to constrain the size of emission of complex molecules. For this, I carried out interferometric observations of the two brightest hot corinos: this emission is compact (<150 AU) with, in one of the sources, an extended component originating from the cooler, less dense outer envelope. The third goal consisted in confronting the possible formation pathways with the results of my observations to try and discriminate whether complex organic molecules form via gas-phase or grain-surface reactions. Although it was not possible to arrive at a definite answer, my data seem to favor the later formation route. Moreover, the comparison of hot corinos and their high-mass analogs, the hot cores (showing that complex molecules are relatively more abundant in hot corinos), also support grain-surface synthesis of these molecules
Robert, Jasmin. "Méthodes de détection et de classification des naines brunes". Thèse, 2006. http://hdl.handle.net/1866/8055.
Pełny tekst źródłaAllain, Stephanie. "L'évolution du moment cinétique des étoiles pré-séquence principale de faible masse". Phd thesis, 1997. http://tel.archives-ouvertes.fr/tel-00686694.
Pełny tekst źródłaMalo, Lison. "Recherche et caractérisation des étoiles jeunes de faible masse dans le voisinage solaire". Thèse, 2014. http://hdl.handle.net/1866/11419.
Pełny tekst źródłaPrès de 70% des étoiles de la Galaxie ont une masse inférieure à ~0.8 Msun. Cependant, étant donné que ces étoiles sont plus difficilement observables en raison de leur plus faible luminosité, cette statistique ne reflète pas le recensement actuel de la population d'étoiles de faible masse dans le voisinage solaire, ni dans les groupes cinématiques d'étoiles jeunes. Cette population a une grande importance pour contraindre la forme de la fonction de masse Galactique, et aussi pour contraindre les modèles évolutifs. Les étoiles de faible masse sont aussi d'excellentes cibles pour la recherche d'exoplanètes avec des techniques variées (imagerie directe, vitesse radiale, transit). La caractérisation des exoplanètes autour de ces étoiles est tributaire des connaissances fondamentales sur celles-ci, c'est-à-dire de leur luminosité bolométrique, température effective, rayon et âge. Dans la présente thèse, dont le but est d'identifier et caractériser les étoiles de faible masse, une méthode statistique a été développée afin d'établir quantitativement l'appartenance d'une étoile à un groupe en dérivant une probabilité d'association. Cette méthode combine l'inférence Bayesienne et des modèles empiriques de plusieurs observables, dont la luminosité, vitesse spatiale et position galactique, de membres confirmés de 7 groupes d'étoiles jeunes (8-120 Mans) ainsi que d'étoiles vieilles du champ. Les étoiles ayant une probabilité d'association minimale de 90% sont considérées comme des candidates. L'analyse développée prédit aussi la vitesse radiale et la distance trigonométrique qu'une étoile aurait dans une association donnée. L'analyse a montré, pour les 177 membres confirmés, un excellent accord entre les paramètres prédits et observés, soit de 1.9 km/s et 10% respectivement, pour la vitesse radiale et la parallaxe. La mesure de ces paramètres pour les candidates est donc une bonne manière de confirmer leur appartenance à l'association. Cette méthode robuste a été appliquée sur un échantillon de 758 étoiles montrant des signes de jeunesse (émission H$\alpha$ et rayons X). L'analyse a permis d'identifier 214 candidates hautement probables, et le suivi spectroscopique de ces étoiles a permis, jusqu'à présent, de confirmer la justesse de la prédiction en vitesse radiale pour 130 étoiles. Ces observations spectroscopiques ont aussi permis de mesurer leur vitesse de rotation, qui s'est avérée élevée comparativement aux étoiles vieilles du champs. La mesure de la distance trigonométrique était aussi en accord avec la prédiction pour 18 candidates jeunes. Grâce aux membres dont l'appartenance à un groupe jeune a été confirmée, un modèle empirique de la luminosité en rayon X des étoiles a pu être établi. Cette luminosité s'est avérée significativement plus élevée (environ 4 fois plus) pour les étoiles des groupes les plus jeunes (~8-12 Mans) que pour celles des groupes plus vieux (~120 Mans). Cet observable constitue donc un bon indicateur d'âge. La comparaison des spectres de 59 candidates à des modèles d'atmosphère a permis de déterminer trois paramètres fondamentaux: la luminosité bolométrique, la température effective et le rayon. Globalement, les candidates jeunes ont une luminosité plus élevée et un rayon plus grand que les étoiles vieilles. De récents modèles évolutifs incluant le traitement d'une dynamo de type rotationnel et générant un champ magnétique de surface de 1 à 2.5 kGauss ont été utilisés pour déterminer l'âge isochronal de ces étoiles. Les âges ainsi déterminés pour les étoiles de l'association \beta Pictoris en utilisant des étoiles de types spectraux différents sont davantage cohérents (types K5V-M0V: 24 Mans, types M1V-M4V: 14 Mans) et sont aussi cohérents avec l'âge déterminé indépendamment pour le groupe en utilisant l'abondance du lithium des membres de faible masse (26 Mans).
About 70% of the stars in the Galaxy have a mass inferior than ~0.8 Msun. However, this statistic does not reflect the current census population of low mass in the solar neighborhood and in young kinematic groups, since their low luminosity make their observation more difficult. This population is of great interest to check the validity of the Galactic mass function, and also to constraint evolutionary models. The low-mass stars are also excellent targets for the search for exoplanets using various techniques (direct imaging, radial velocity, transit). The characterization of the exoplanets orbiting these stars depends mostly on our basic knowledge of the host star, that is their bolometric luminosity, effective temperature, radius and age. The present thesis aim to identify and characterize low-mass stars. Toward that end, a statistical method has been developed to determine quantitatively the membership probability of a star to a young kinematic group. This method combines the Bayesian inference and empirical models of several observables such as the brightness, Galactic space velocity and position of bona fide members of 7 young stars groups (8-120 Mans), as well as old field stars. Stars with a membership probability greater than 90% are considered candidate members. The analysis also predicts the radial velocity and distance that a star would have if it was an actual member. For the 177 previously-known members, an excellent agreement was found between the predicted and observed parameters (1.9 km/s and 10% for the radial velocity and parallax, respectively). Measuring these observables for the candidates stars is thus a good way to confirm their membership. This robust method was applied to a sample of 758 stars which showed signs of youth (H$\alpha$ and X-ray emission). It allowed to identify 214 highly probable candidates. The spectroscopic follow-up yields a radial velocity in agreement with predictions for 130 stars. These spectroscopic observations also allowed to measure their projected rotational velocity, which turned out to be higher than that of the old population of stars. Trigonometric distance measurements were also obtained and were coherent with predictions for 18 young candidates. Using the confirmed members, a new empirical model of the X-ray luminosity was developed. The X-ray luminosity was found to be about 4 times higher for stars around ~8-12Myr than for older, ~120Myr stars, thus, this observable is a good age indicator in this range. Comparing the spectra of 59 young candidate members to atmosphere models allowed to determine three basic parameters: the bolometric luminosity, the effective temperature and the radius. Overall, these candidates are more luminous and have a greater radius than old stars. Recent evolutionary models that include the rotational dynamo-type treatment and produce magnetic field strength of 1 to 2.5 kGauss were used to derive an isochronal age for each star. The ages determined for \beta Pictoris moving group members using stars of different spectral types are coherent with one another (types K5V-M0V: 24 Mans, types M1V-M4V: 14 Mans) and are also coherent with age determined independently using lithium abundance of the low-mass members (26 Mans).
Gagné, Jonathan. "La recherche de naines brunes et étoiles de faible masse dans les associations cinématiques jeunes du voisinage solaire". Thèse, 2015. http://hdl.handle.net/1866/12348.
Pełny tekst źródłaThe main objective of this thesis is the identification of low-mass star and brown dwarf members of young moving groups in the solar neighborhood. These associations are typically younger than 200 million years and include stars formed at the same time and in the same environment. The majority of their members with masses approximately larger than 0.3 times that of the Sun have already been discovered, however the less massive, fainter members are still elusive. Their identification will allow us to address several fundamental questions in astrophysics. In particular, uncovering young objects that are still warm because of their recent formation will allow us to probe masses down to only a few times the mass of Jupiter, a mass regime which is still poorly understood. They will allow us to constrain the initial mass function and explore the connection between brown dwarfs and exoplanets, given that the least massive brown dwarfs have physical properties similar to those of gaseous giant exoplanets. In order to carry through this project, we have adapted the BANYAN I statistical tool to make it applicable to very low-mass objects in addition to bringing several improvements to the tool. We have included the use of two near-infrared color-magnitude diagrams that allow differentiating young low-mass stars and brown dwarfs from older objects, we added the use of prior probabilities to make its results more realistic, we adapted spatial and kinematic models of moving groups using tridimensional gaussian ellipsoids with axes free to rotate, we performed a Monte Carlo analysis to characterize the rate of false-positive and false-negatives, and we revised the structure of its source code to make it more efficient. As a first step, we have used this new algorithm, BANYAN II, to identify 25 new candidate members among a sample of 158 known young low-mass stars (with spectral types > M4) and brown dwarfs. We have then performed a cross-correlation of two all-sky near-infrared catalogs consisting of ~ 500 million celestial objects to identify approximately 100 000 brown dwarf and low-mass star candidates in the solar neighborhood. We have identified a few hundred promising young association members in this sample with the BANYAN II tool, and have performed a near-infrared spectroscopic survey to characterize them. The work presented here has led to the identification of 79 candidate young brown dwarfs and 150 candidate young low-mass stars, and a spectroscopic follow-up allowed us to confirm the young age of 49 brown dwarfs and 62 low-mass stars. We have thus boosted the number of known young brown dwarfs by a factor ~ 2, opening the door to a statistical characterization of their population. These new young brown dwarfs represent an ideal laboratory to better understand the atmospheres of gaseous giant exoplanets. We have identified the first signs of a turn-up in the initial mass function of very low-mass brown dwarfs in the Tucana-Horologium association, which could indicate that exoplanet scattering plays a significant role in composing their population. Results from this spectroscopic follow-up has allowed us to construct an complete empirical sequence of spectral types M5-L5 for field dwarfs, low-gravity (β) and very low-gravity (γ) dwarfs. We have performed a comparison of these new data with evolution and atmosphere models, and constructed a set of empirical spectral type-magnitude and color-magnitude sequences for young brown dwarfs. Finally, we have discovered two new exoplanets from a direct-imaging follow-up of low-mass stars discovered as part of this project. The future GAIA mission and the complete spectroscopic follow-up of the candidates presented in this thesis will allow to confirm their membership and to constrain the initial mass function in the substellar regime.
Malo, Lison. "Recherche d’étoiles jeunes de faible masse dans le voisinage solaire". Thèse, 2009. http://hdl.handle.net/1866/3701.
Pełny tekst źródłaThe gravitational collapse of a molecular gas cloud produces the incipient stars with various masses between 0.08 and approximately 100 M . The majority of the stellar galactic population is made up of stars with masses lower than approximately 0.6 M . The last event of stellar formation in the solar neighborhood happened in the local bubble no more than 100 million of years ago, probably caused by the propagation of a shock wave in the galactic local arm. This is how young associations, also called moving groups were formed. Their members are characterized by a common velocity and position within the Galaxy. Young associations, being sparsely populated and relatively close to the Sun, their members are found all over the sky. So far, only the most massive members (luminous ones) have been identified. Young low-mass stars, comprising the majority of the population, remain to be identified. Those stars are expected to be excellent candidates to find exoplanets through direct imaging techniques, while also forming a key population to constrain M stars and brown dwarfs evolutionnary models. This master thesis presents a new method using a kinematical model coupled with a Bayesian statistic analysis to identify young low-mass stars in the beta Pictoris, Tucana- Horologium and AB Doradus associations. Using a sample of 1080 K and M stars, all showing youth indicators such as Halpha emission and X-rays luminosity, their photometric and kinematic properties (proper motion) are analyzed to extract 98 highly probable members distributed over the three associations. Status confirmation as members will require measurement of their radial velocity (predicted by our analysis) and the lithium at 6708 Å equivalent widths to better constrain their age.
Naud, Marie-Eve. "Recherche et caractérisation d'exoplanètes à grande séparation autour d'étoiles jeunes de faible masse". Thèse, 2016. http://hdl.handle.net/1866/20606.
Pełny tekst źródłaLagarde, Nadège. "Mélange induit par rotation et instabilité thermohaline dans les étoiles de faible masse et de masse intermédiaire. Conséquences sur l'évolution des éléments légers dans la Galaxie". Phd thesis, 2012. http://tel.archives-ouvertes.fr/tel-00754970.
Pełny tekst źródłaDel, Duchetto Karl. "Dispersion de la couleur J-K des naines brunes de type L2". Thèse, 2014. http://hdl.handle.net/1866/10718.
Pełny tekst źródłaBrown dwarfs are objects with a mass intermediate between that required to form a star and that of a planet. Brown dwarfs are classified, from higher to lower temperature, under spectral types L, T and Y, caracterized by a J-K average color that varies from 1.2 to 1.8 for types L0 to L8, and from 1.8 to -0.5 for types L8 to T8. Furthermore, the J-K color of some spectral types presents more than a magnitude of dispersion. This study attempts to explain the large dispersion of the J-K color of the type L2 brown dwarfs. Observations were made with the infrared camera CPAPIR at the Observatoire du Mont Mégantic. We targeted a total of 22 brown dwarfs that were observed in the K band, and 12 among them were also observed in the J band. Each brown dwarf was calibrated with a standard star, which makes our data independent from those of 2MASS. We observe a correlation between the J-K colors obtained from our data and those from 2MASS. This shows that the large J-K dispersion in the data is due to brown dwarf physical properties and not to observational errors. Consideration of the factors that could be responsible for this large dispersion, namely the spectral classification, the metallicity, the surface gravity, an unresolved binarity, the presence of clouds and rotation, shows that surface gravity is the factor most likely to explain the large J-K color dispersion.
Lachapelle, François-René. "Caractérisation photométrique et spectroscopique de compagnons sous-stellaires de faible masse autour d'étoiles de la région de formation Upper Scorpius". Thèse, 2013. http://hdl.handle.net/1866/10721.
Pełny tekst źródłaFollowing the discovery of about 2000 brown dwarfs over the past two decades, we begin to understand the physics of these objects of mass intermediate between stellar and planetary masses. Nevertheless, the atmosphere and evolution models for these low-mass objects are still struggling to reproduce their characteristics at young ages. This work presents the characterization of four sub-stellar mass (8-30 MJup) companions orbiting at large separation (300-900 AU) around young stars (5 Myr) in the Upper Scorpius formation region. New spectra (0,9-2,5 um) and new photometric measurements (YJHKsL') are presented and analyzed in order to determine the mass, effective temperature, luminosity and surface gravity of these companions, while assessing the fidelity with which the synthetic spectra from two recent atmosphere models reproduce the observed spectra.