Optical long baseline interferometry was recently established as a technique capable of resolving stars and their circumstellar environments at the milliarcsecond (mas) resolution level. This high-resolution opens an entire new window to the study of astrophysical systems, providing information inaccessible by other techniques. Astrophysical disks are observed in a wide variety of systems, from galaxies up to planetary rings, commonly sharing similar physical processes. Two particular disk like systems are studied in the thesis: (i) B He-rich stars that exhibits magnetic fields in order of kG and that trap their winds in structures called magnetospheres; and (ii) Be stars, fast rotating stars that create circumstellar viscous disks. This study uses the interferometric technique to investigate both the photosphere proper and the circumstellar environment of these stars. The objective is to combine interferometry with other observational techniques (such as spectroscopy and polarimetry) to perform a complete and well-constrained physical description of these systems. This description is accompanied by radiative transfer models performed by the HDUST code. / Interferometria óptica de longa linha de base recentemente estabeleceu-se como uma técnica capaz de resolver estrelas e seus ambientes circunstelares no nível de mili segundos de arcos (\\textit). Esta alta resolução abre uma janela inteiramente nova para o estudo de sistemas astrofísicos, fornecendo informações inacessíveis por outras técnicas. Discos astrofísicos são observados numa ampla variedade de sistemas, de galáxias à discos planetários, em geral compartilhando de processos físicos similares. Dois sistemas de discos foram estudados nesta tese: (i) o estrelas B ricas em He e que possuem campos magnéticos da ordem de kG e que confinam seus ventos em estruturas chamadas magnetosferas; e (ii) estrelas Be, estrelas de rotação rápida que criam um disco circumstelar viscoso. Este estudo usa a técnica interferométrica para investigar ambas a própria fotosfera e o ambiente circunstelar destas estrelas. O objetivo é combinar a interferometria com outras técnicas observacionais (tal como espectroscopia e polarimetria) para realizar uma descrição física completa e precisa destes sistemas. Esta descrição é acompanhada por modelos de transferência radiativa executados pelo código HDUST.

Cette thèse s'inscrit dans la thématique de l'étude de la formation et de l'évolution des systèmes planétaire grâce à la méthode de l'imagerie à haut contraste, aussi appelée imagerie directe, par comparaison aux méthodes de détection dites "indirectes". Le travail que je présente dans ce manuscrit s'articule en deux parties bien distinctes. La première partie concerne la composante observationnel de ma thèse, à l'aide de l'instrument SPHERE installé au Very Large Telescope, au sein du consortium du même nom. L'instrument SPHERE a pour objectif la détection et la caractérisation de jeunes et massives exoplanètes mais également de disques circumstellaires allant des très jeune disques protoplanétaires aux disques de débris, plus âgés. Ainsi, je présente dans ce manuscrit ma contribution au programme SHINE, un grand relevé de 200 nuits dont le but est la détection de nouvelles exoplanètes ainsi que la caractérisation spectrale et orbitale des quelques compagnons déjà connus. J'y présente également les deux études de disques circumstellaires que j'ai réalisées, autour des étoiles HD 141569 et HIP 86598. La première étude ayant permis la découverte d'anneaux concentriques à quelques dizaine d'UA de l'étoile ainsi que de asymétrie dans le flux du disque inhabituelle. La seconde étude porte sur la découverte d'un disque de débris présentant également une asymétrie en flux inhabituelle. La deuxième partie concerne la composante instrumentale de mon travail de thèse, au sein du consortium MICADO, en charge de la conception de la caméra du même nom qui sera l'un des instruments de première lumière de l'Extremely Large Telescope Européen (ELT). Dans ce manuscrit, je présente l'étude que j'ai menée afin de définir le design de certain composant du mode coronographique de MICADO tout en tenant compte des contraintes de l'instrument qui n'est pas dédié à l'imagerie haut contraste, contrairement à SPHERE. / This thesis is performed in the context of the study of the formation and evolution of planetary systems using high contrast imaging, also known as direct imaging in contrast to so-called "indirect" detection methods. The work I present in this manuscript is divided into two distinct parts.The first part concerns the observational component of my thesis, using the SPHERE instrument installed at Very LargeTelescope. This work was done as part of the consortium of the same name. The purpose of the SPHERE instrument is to detect and characterize young and massive exoplanets, but also circumstellar disks ranging from very young protoplanetary disks to older debris disks. In this manuscript, I present my contribution to the program SHINE, a large survey with an integration time of 200 nights' worth of observation, the goal of which is the detection of new exoplanets and the spectral and orbital characterization of some previously-known companions. I also present the two studies of circumstellar disks that I made, around the stars HD 141569 and HIP 86598. The first study allowed the discovery of concentric rings at about ten AU of the star along with an unusual flux asymmetry in the disk. The second study is about the discovery of a debris disk that also has an unusual flux asymmetry. The second part concerns the instrumental component of my thesis work done within the MICADO consortium, in charge of the design of the camera of the same name which will be one of the first light instruments of the European Extremely Large Telescope (ELT). In this manuscript, I present the study in which I define the design of some components of the coronagraphic mode of MICADO while taking into account the constraints of the instrument - which is not dedicated to high contrast imaging, unlike SPHERE.

The existence of other habitable worlds and the possible development of life elsewhere in the Universe have been among mankinds fundamental questions for thousands of years. These interrogations about our origins and place in the Universe are today at the dawn of being answered in scientific terms. The key year was 1995 with the discovery of the first extrasolar planet orbiting around a solar-type star. About 400 extrasolar planets are known today and the possibility to identify habitable worlds and even life among them largely contributes to the growing interest about their nature and properties. However, characterizing planetary systems is a very difficult task due to both the huge contrast and the small angular separation between the host stars and their environment. New techniques have emerged during the past decades with the purpose of tackling these fantastic observational challenges. In that context, infrared interferometry is a very promising technique, since it provides the required angular resolution to separate the emission of the star from that of its environment. This dissertation is devoted to the characterization of extrasolar planetary systems using the high angular resolution and dynamic range capabilities of infrared interferometric techniques. The first part of the present work is devoted to the detection with current interferometric facilities of warm dust within the first few astronomical units of massive debris discs around nearby stars. In order to extend the imaging of planetary systems to fainter discs and to extrasolar planets, we investigate in a second step the performance of future space-based nulling interferometers and make a comparison with ground-based projects. Finally, the third part of this work is dedicated to the impact of exozodiacal discs on the performance of future life-searching space missions, the goal being to characterize extrasolar planets with sizes down to that of the Earth.

Le relevé DEBRIS est effectué par le télescope spatial Herschel. Il permet d’échantillonner les disques de débris autour d’étoiles de l’environnement solaire. Dans la première partie de ce mémoire, un relevé polarimétrique de 108 étoiles des candidates de DEBRIS est présenté. Utilisant le polarimètre de l’Observatoire du Mont-Mégantic, des observations ont été effectuées afin de détecter la polarisation due à la présence de disques de débris. En raison d’un faible taux de détection d’étoiles polarisées, une analyse statistique a été réalisée dans le but de comparer la polarisation d’étoiles possédant un excès dans l’infrarouge et la polarisation de celles n’en possédant pas. Utilisant la théorie de diffusion de Mie, un modèle a été construit afin de prédire la polarisation due à un disque de débris. Les résultats du modèle sont cohérents avec les observations. La deuxième partie de ce mémoire présente des tests optiques du polarimètre POL-2, construit à l’Université de Montréal. L’imageur du télescope James-Clerk-Maxwell passe de l’instrument SCUBA à l’instrument SCUBA-2, qui sera au moins cent fois plus rapide que son prédécesseur. De même, le polarimètre suit l’amélioration et un nouveau polarimètre, POL-2, a été installé sur SCUBA-2 en juillet 2010. Afin de vérifier les performances optiques de POL-2, des tests ont été exécutés dans les laboratoires sub-millimétriques de l’Université de Western Ontario en juin 2009 et de l’Université de Lethbridge en septembre 2009. Ces tests et leurs implications pour les observations futures sont discutés. / The DEBRIS survey, being performed by the space telescope Herschel, is an unbiased sampling of the debris disks candidates in the solar neighbourhood. In the first part of this thesis, a ground-based polarimetric survey of 108 DEBRIS candidate stars is presented. Using the polarimeter, “La Belle et la Bete,” at the Mont-Megantic Observatory, observations were carried out in order to detect polarization induced by the presence of a debris disk. Due to a low rate of detection, a statistical analysis was performed to compare the polarization between stars owning a debris disk with stars without one. Using Mie scattering theory, a basic model was constructed to estimate the level of polarization produced by dust grains in a debris disk. The results of this model are consistent with our observations. The second part of the thesis presents the optical tests of the polarimeter POL-2, built at Université de Montréal. The James Clerk-Maxwell-Telescope imager SCUBA has been upgraded to SCUBA-2, which is more than one hundred times faster than its predecessor with 500 times more pixels. Likewise, the polarimeter follows the improvement as a new polarimeter, POL-2, was installed on SCUBA-2 in July 2010. In order to verify the optical performance of POL-2, tests were completed at the submillimeter laboratories at the University of Western Ontario in June 2009, and the University of Lethbridge in September 2009. These tests and their implications for future observations are discussed.

No description available.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / We present a multi-wavelength study of the stellar content of 11 optical/infrared Southern Galactic Hii regions with 10 h < α(J2000) < −17 h and −65° < δ(J2000) < −35°. Nine optical objects with no published or uncertain distances were examined in order to identify their ionising sources and to determine their distances, whereas young stellar objects (YSOs) and main sequence ionising stars were photometrically classified in the two infrared clusters. We carried out optical spectroscopy and UBV photometry of the stellar content of these Hii regions and obtained the distance of individual stars by spectroscopic parallax. To avoid using a fixed value for the total-to-selective extinction ratio RV , the reddening AV was determined directly by the colour-difference method. We classified as types O or B 24 out of the 31 stars for which optical spectra were obtained. In particular, we identified two new O stars in RCW98 and RCW99. The values for reddening obtained correspond to a mean hRV i = 3.44, which is about 10% higher of the mean value found for field stars over all directions of the Galaxy. For the Hii regions NGC3503, NGC6334, RCW55, RCW87, RCW98 e RCW99, we obtained more precise distances calculated as the median of the spectroscopic parallaxes obtained for two to six different stars in each nebulae, with an internal dispersion of less than 5%. Among the objects more obscured in the Norma region, we analysed the stellar content of the East part of the large complex of Hii regions GAL331.5-00.1, which contains eight bright extended radio sources. This study comprises the infrared clusters [DBS2003] 156 and [DBS2003] 157, respectively associated to Hii regions GAL331.11-00.51 and GAL331.31-00.34. In order to isolate the brightest 2MASS sources of their unresolved companions, we carried out JHK photometry with resolution better than 2MASS data. 47 Near-infrared (NIR) sources with Ks-band excess were identified following usual methods. Other 70 YSOs were also identified by using Mid-IR on-line data of the GLIMPSE survey. The search for radial-velocity measurements in the literature and the similarity between the stellar population explored have indicated the two regions as physically associated. With the determination of the spectroscopic parallaxes of four O-type and two B-type stars spread over the both clusters, this hypothesis was verified. The parallaxes of these 6 stars returned very compatible distances (hdhelioci = 3.30 ± 0.29 kpc). The Near- and Mid-IR counterparts of the IRAS source 16085-5138 was found close to the field of [DBS2003] 157. This source has showed typical colours of a Ultra-compact ii region (UCHii) and spectral index α = 3.6 between 2 and 25 μm, which is typical of YSOs immersed in protostellar envelopes. A lower limit to the bolometric luminosity of the protostar embedded was computed as L = 7.7×103L⊙ (M = 10M⊙), which corresponds to a BO-B1 zero-age star. The cluster [DBS2003] 157 was found to be spread over all ∼4′ × 4′ region demarcated by a intense shell-like dust emission, where a secondary massive star formation is going on, likely as a result of the interaction between this dust and stellar winds. / Apresentamos aqui um estudo multibanda do conteúdo estelar de onze regiões Hii do Hemisfério sul com 10 h < α(J2000) < −17 h e −65◦ < δ(J2000) < −35◦. Em 9 objetos ópticos, com valores de distância discrepantes ou sem nenhuma determinação anterior publicada, visamos identificar as fontes ionizantes e determinar suas distâncias, enquanto que, no estudo de dois outros objetos no infravermelho, buscamos não apenas identificar as fontes ionizantes, mas também objetos estelares jovens (YSOs) em seus campos. Nos primeiros, realizamos espectroscopia no óptico e fotometria UBV de seus conteúdos estelares e determinamos as distâncias das estrelas massivas por meio da paralaxe espectroscópica. A fim de evitar o uso de um valor fixo para a razão entre a extinção total e a seletiva à banda V , RV , a extinção AV na direção de cada estrela foi determinada diretamente através no método das diferenças de cor. De um total de 31 estrelas espectroscopicamente estudas, 24 foram classificadas como tipos O ou B, sendo duas novas estrelas tipo O encontradas em RCW98 e RCW99. As estimativas de AV implicaram um valor médio de hRV i = 3.44. Este resultado supera em 10% o valor médio encontrado para estrelas de campo sobre todas as direções da Galáxia. Para as regiões Hii NGC3503, NGC6334, RCW55, RCW87, RCW98 e RCW99, distâncias mais precisas foram estimadas como o valor mediano da paralaxe espectroscópica de 2 a 6 diferentes estrelas ionizantes, resultando em uma dispersão interna menor que 5%. Dentre os objetos mais obscurecidos pela extinção interestelar da região de Norma, analisamos o conte´udo estelar da região leste do grande complexo de regiões Hii brilhantes em radiofrequências GAL331.5-00.1. A área estudada engloba os aglomerados infravermelhos [DBS2003] 156 e [DBS2003] 157, respectivamente associados às regiões Hii GAL331.11-00.51 e GAL331.31-00.34. Observações fotométricas nas bandas J, H e Ks, com mais alta resolução que a fotometria 2MASS, foram realizadas nas direções desses objetos, o que possibilitou isolar as fontes infravermelhas mais brilhantes de estrelas companheiras não resolvidas e selecionar potenciais estrelas ionizantes para subsequente espectroscopia. 47 fontes com excesso de emissão intrínseca na banda Ks, típico em YSOs, foram identificadas seguindo os métodos usuais de análise da fotometria no IR próximo (NIR). Outros 70 YSOs foram identificados no IR médio (Mid-IR) usando dados do survey GLIMPSE. A pesquisa por medidas de velocidade radial na direção desses dois objetos e a semelhança das populações estelares indicou que as duas sub-regiões estudas deveriam estar fisicamente associadas. Esta hipótese foi reafirmada com a determinação da paralaxe espectroscópica de 4 estrelas tipo O e outras 2 tipo B nos dois aglomerados, que retornaram valores de distâncias heliocêntricas bastante compatíveis (hdhelioci = 3.30 ± 0.29 kpc). A contrapartida nos NIR e Mid-IR da fonte IRAS 16085-5138 foi encontrada junto ao aglomerado [DBS2003] 157. Esta fonte apresentou cores típicas de uma região Hii Ultracompacta (UCHii) e índice espectral entre 2 e 25 μm de α = 3.6, típico de YSO imerso em um envelope protoestelar. Um limite inferior para a luminosidade bolométrica da protoestrela embebida foi estimado em L = 7.7×103L⊙ (M = 10M⊙), o que corresponde a uma estrela de idade zero na faixa de BO-B1. O aglomerado [DBS2003] 157 mostrou-se estar espalhado sobre toda uma região de ∼4′ ×4′, demarcada por intensa emissão de poeira quente e espacialmente distribuída como uma nuvem em forma de concha.

Au moins 20% des étoiles de la séquence principale abritent des disques de débris, analogues à la ceinture de Kuiper. Ces disques sont la preuve que l'accumulation de solides a au moins permis la formation de corps de taille kilométrique. Il n'est donc pas surprenant que plusieurs de ces disques soient accompagnés de planètes, qui, en laissant leur empreinte dynamique sur la structure spatiale de ces disques, révèlent leur présence. Par conséquent, la détection d'un disque de débris excentrique entourant Zeta² Ret par le télescope spatial Herschel indique la présence d'un perturbateur massif dans ce système. Zeta² Ret étant un système mature, âgé de 2-3 Gyr, et en ce sens, analogue à notre propre système solaire, il offre un exemple différent d'évolution dynamique à long terme. Cette thèse comprend une modélisation détaillée de la structure du disque de débris de Zeta² Ret, ce qui conduit à des contraintes sur la masse et l'orbite du perturbateur suspecté. Cette étude révèle également que les structures excentriques dans les disques de débris peuvent survivre sur des échelles de temps Gyr.La modélisation de disques de débris peut permettre la découverte postérieure de planètes comme c'est le cas pour le système de Fomalhaut. La forme excentrique de son disque de débris fut d'abord attribuée à Fom b, un compagnon détecté près du bord interne du disque, mais qui se révèle finalement trop excentrique (e~0.6-0.9) pour lui donner sa forme, indiquant la présence d'un autre corps massif, Fom c. Le système planétaire qui en résulte est très instable, ce qui implique une diffusion récente de Fom b sur son orbite actuelle, éventuellement par Fom c. L'étude de ce scénario révèle qu'en ayant résidé dans une résonance de moyen-mouvement interne avec une Fom c excentrique et de masse comparable à Neptune ou Saturne, Fom b aurait subi une augmentation progressive de son excentricité sur des périodes comparables à l'âge du système (~440 Myr), ce qui l'aurait amenée assez proche de Fom c pour subir une diffusion récente, qui, complétée par une évolution séculaire avec Fom c, explique sa configuration orbitale actuelle. Ce mécanisme en trois étapes pourrait également avoir généré d'importantes quantités de matériel en orbites très excentriques, ce qui en retour pourrait alimenter en poussière les parties internes du système. Par conséquent, ce mécanisme pourrait aussi expliquer la présence de ceintures de poussières internes dans le système de Fomalhaut, mais aussi la découverte d'une importante population de ceintures de poussières chaudes et massives dans les systèmes âgés de plus de 100 Myr.Les systèmes planétaires découverts jusqu'ici présentent une grande variété d'architectures, et notre système solaire est loin d'être un modèle générique. Un des principaux mécanismes déterminant la morphologie d'un système planétaire est la migration planétaire. On attend d'un compagnon stellaire - ce que notre système solaire ne possède pas - qu'il affecte les conditions de migration planétaire, et conduise potentiellement à la formation de systèmes planétaires très différents. Ce phénomène est évidemment non négligeable puisque les systèmes binaires représentent au moins la moitié des systèmes stellaires. Dans les systèmes planétaires matures, la migration planétaire peut se produire suite à l'interaction avec le matériel solide et l'impact de la binarité sur cette migration tardive est exploré dans cette thèse. Un compagnon circumstellaire pourrait inverser la tendance à la migration interne des planètes dans les systèmes stellaires simples, et rapprocher ces planètes des régions perturbées par le compagnon binaire, où elles ne pourraient pas s'être formées in situ. Cela pourrait fournir une explication à la présence de planètes qui présentent des signes de migration externe vers un compagnon circumstellaire dans les systèmes de Gamma Cephei et HD 196885. / At least 20% of Main-Sequence stars are known to harbor debris disks analogs to the Kuiper Belt. These disks are proof that the accretion of solids has permitted the formation of at least km-sized bodies. It is thus not surprising that several of these disks are accompanied by planets, which may reveal themselves by setting their dynamical imprints on the spatial structure of debris disks. Therefore, the detection of an eccentric debris disk surrounding Zeta² Ret by the Herschel space telescope provides evidence for the presence of a massive perturber in this system.Zeta² Ret being a mature Gyr-old system, and in that sense, analogous to our own Solar System, it offers a different example of long-term dynamical evolution. This thesis includes a detailed modeling of the structure of the debris disk of Zeta² Ret, which leads to constraints on the mass and orbital characteristics of the putative perturber. This study also reveals that eccentric structures in debris disks can survive on Gyr timescales.Detailed modeling of the structure of debris disks can allow the posterior discovery of hidden planets as is the case for the Fomalhaut system. The eccentric shape of the debris disk observed around this star was first attributed to Fom b, a companion detected near the belt inner-edge, which revealed to be highly eccentric (e~0.6-0.9), and thus very unlikely shaping the belt. This hints at the presence of another massive body in this system, Fom c, which drives the debris disk shape. The resulting planetary system is highly unstable, which involves a recent scattering of Fom b on its current orbit, potentially with the yet undetected Fom c. This scenario is investigated in this thesis and its study reveals that by having resided in inner mean-motion resonance with a Neptune or Saturn-mass belt-shaping eccentric Fom c and therefore have suffered a gradual resonant eccentricity increase on timescales comparable to the age of the system (~440 Myr), Fom b could have been brought close enough to Fom c and suffered a recent scattering event, which, complemented by a secular evolution with Fom c, explains its current orbital configuration. This three-step scenario also implies that significant amounts of material may have been set on extremely eccentric orbits such as this of Fom b through this mechanism, which in return could feed in dust the inner parts of the system. Therefore, this mechanism may also explain the presence of inner dust belts in the Fomalhaut system, but also the discovery a significant population of very bright hot dust belts in systems older than 100 Myr.The planetary systems discovered so far exhibit a great variety of architectures, and our solar system is far from being a generic model. One of the main mechanism that determines a planetary system morphology is planetary migration. The presence of a stellar binary companion - which our solar system is deprived of - is expected to affect planetary migration conditions, and potentially lead to the formation of very different planetary systems. This phenomenon is obviously non-negligible since binary systems represent at least half of stellar systems. At late stages of planetary systems formation, planetary migration may occur as the result of interactions with remaining solid planetesimals and the impact of binarity on this planetesimal-driven migration is explored in this thesis. A stellar binary companion may in fact reverse the tendency for planets in single star systems to migrate inwards, and bring them closer to regions perturbed by the binary companion, where they could not have formed in situ. This may give an explanation for the presence of planets which present signs of outward migration towards a circumstellar companion in the Gamma Cephei and HD 196885 systems.

Optical long baseline interferometry was recently established as a technique capable of resolving stars and their circumstellar environments at the milliarcsecond (mas) resolution level. This high-resolution opens an entire new window to the study of astrophysical systems, providing information inaccessible by other techniques. Astrophysical disks are observed in a wide variety of systems, from galaxies up to planetary rings, commonly sharing similar physical processes. Two particular disk like systems are studied in the thesis: (i) B He-rich stars that exhibits magnetic fields in order of kG and that trap their winds in structures called magnetospheres; and (ii) Be stars, fast rotating stars that create circumstellar viscous disks. This study uses the interferometric technique to investigate both the photosphere proper and the circumstellar environment of these stars. The objective is to combine interferometry with other observational techniques (such as spectroscopy and polarimetry) to perform a complete and well-constrained physical description of these systems. This description is accompanied by radiative transfer models performed by the HDUST code. / Interferometria óptica de longa linha de base recentemente estabeleceu-se como uma técnica capaz de resolver estrelas e seus ambientes circunstelares no nível de mili segundos de arcos (\\textit). Esta alta resolução abre uma janela inteiramente nova para o estudo de sistemas astrofísicos, fornecendo informações inacessíveis por outras técnicas. Discos astrofísicos são observados numa ampla variedade de sistemas, de galáxias à discos planetários, em geral compartilhando de processos físicos similares. Dois sistemas de discos foram estudados nesta tese: (i) o estrelas B ricas em He e que possuem campos magnéticos da ordem de kG e que confinam seus ventos em estruturas chamadas magnetosferas; e (ii) estrelas Be, estrelas de rotação rápida que criam um disco circumstelar viscoso. Este estudo usa a técnica interferométrica para investigar ambas a própria fotosfera e o ambiente circunstelar destas estrelas. O objetivo é combinar a interferometria com outras técnicas observacionais (tal como espectroscopia e polarimetria) para realizar uma descrição física completa e precisa destes sistemas. Esta descrição é acompanhada por modelos de transferência radiativa executados pelo código HDUST.

Stars form from the collapse of molecular clouds and evolve in an environment rich in gas and dust before becoming Main Sequence stars. During this phase, characterised by the presence of a protoplanetary disc, stars manifest changes in the structure and luminosity. This thesis performs a multi-wavelength analysis, from optical to mm range, on a sample of young stars (YSOs), mainly Classical T Tauri (CTTS). The purpose is to study optical and infrared variability and its relation with the protoplanetary disc. Longer wavelength, in the mm range, are used instead to investigate the evolution of the disc, in terms of dust growth. In optical, an F-test on a sample of 39 CTTS reveals that 67\% of the stars are variable. The variability, quantified through pooled sigma, is visible both in magnitude amplitudes and changes over time. Time series analysis applied on the more variable stars finds the presence of quasi periodicity, with periods longer than two weeks, interpreted either as eclipsing material in the disc happening on a non-regular basis, or as a consequence of star-disc interaction via magnetic field lines. The variability of YSOs is confirmed also in infrared, even if with lower amplitude. No strong correlations are found between optical and infrared variability, which implies a different cause or a time shift in the two events. By using a toy model to explore their origin, I find that infrared variations are likely to stem from emissions in the inner disc. The evolution of discs in terms of dust growth is confirmed in most discs by the analysis of the slope of the spectral energy distribution (SED), after correcting for wind emission and optical depth effects. However, the comparison with a radiative transfer model highlights that a number of disc parameters, in particular disc masses and temperature, dust size distribution and composition, can also affect the slope of the SED.

Nous présentons les résultats de trois campagnes d'observation d'un mois chacune dans le cadre de l'étude de la collision des vents dans les systèmes binaires Wolf-Rayet + OB. Ce travail se concentre sur l'étude des objets de l'hémisphère sud n'ayant jamais encore fait l'objet d'études poussées dans ce contexte. À cela, nous avons ajouté l'objet archétype pour ce type de systèmes : WR 140 (WC7pd + O5.5fc) qui a effectué son dernier passage périastre en janvier 2009. Les deux premières campagnes (spectroscopiques), ont permis une mise à jour des éléments orbitaux ainsi qu'une estimation de la géométrie de la zone de collision des vents et d'autres paramètres fondamentaux des étoiles pour 6 systèmes binaires : WR 12 (WN8h), 21 (WN5o+O7V), 30 (WC6+O7.5V), 31 (WN4o+O8), 47 (WN6o+O5) et 140. Une période non-orbitale courte (probablement reliée à la rotation) a également été mesurée pour un des objets : WR 69 (WC9d+OB), avec une période orbitale bien plus grande. La troisième campagne (photométrique) a révélé une variabilité étonnamment faible dans un échantillon de 20 étoiles WC8/9. Cela supporte l'idée que les pulsations ne sont pas courantes dans ce type d'étoiles et qu'il est peu probable que celles-ci soient le mécanisme dominant de formation de poussière, suggérant, par défaut, le rôle prédominant de la collision des vents. / We present the results from three month-long observational campaigns related to WR+O colliding-wind binaries. This work focuses on southern-hemisphere systems that have not yet been previously studied in this context. To this we add the northern archetype colliding-wind system WR 140 (WC7pd + O5.5fc), which recently suffered another active periastron passage in 2009 January. The first two (spectroscopic) campaigns allowed us to update the orbital elements and to constrain the geometry of the colliding wind region and other fundamental parameters, for 6 binary systems: WR 12 (WN8h), WR 21 (WN5o+O7V), WR 30 (WC6+O7.5V), WR 31 (WN4o+O8), WR 47 (WN6o+O5) and WR 140. A short non-orbital (probably rotational) period was also detected in the WR component of one of our objects, WR 69 (WC9d+OB), with a much longer orbital period. The third (photometric) campaign revealed a surprisingly low level of variability in our sample of 20 WC8/9 stars. This supports the idea that pulsations are not very frequent in this type of star and are unlikely to be the main mechanism for dust formation, suggesting, by default, a predominant role of wind-wind collision.