Le travail que je présente dans cette thèse est un travail principalement expérimental effectué au sein du laboratoire LAMAp de l'Université de Cergy-Pontoise, à l'aide du dispositif expérimental appelé FORMOLISM. Les principaux composants de ce dispositif sont: l'ultravide (10-10 mbar), l'ultra-froid (~5 K), des jets atomiques, la spectrométrie de masse TPD (Thermally Programmed Desorption) et la spectroscopie laser dans l'UV mettant en oeuvre des longueurs d'onde autour de ~200 nm. Grâce à la technique REMPI-TOF (Resonantly Enhanced Multi-Photon Ionization – Time Of Flight), nous avons étudié d'une part, la conversion de spin nucléaire de la molécule d'hydrogène H2 sur une surface de glace d'eau amorphe poreuse et d'autre part les processus de formation de cette molécule, qui est la plus abondante dans le milieu interstellaire, sur des surfaces simulant des grains de poussière interstellaire. Les résultats de cette étude présentent un intérêt capital en astrophysique. En effet cette formation ne peut se produire en phase gaz mais peut être expliquée par la rencontre de deux atomes d'hydrogène sur un grain de poussière du milieu interstellaire qui joue le rôle de catalyseur. Différents processus sont impliqués dans la formation de H2 qu'il s'agit d'identifier. Dans ce but, je présente des résultats entièrement nouveaux sur la formation de H2 moléculaire sur une surface de silicate amorphe. Je montre que la molécule peut se former dans un état rovibrationnellement excité de son niveau fondamental jusqu'à une température d'environ 70K et qu'elle est relâchée dans la phase gaz immédiatement après sa formation. Ces résultats démontrent la compétition entre deux mécanismes de formation à très basses température (<18 K) tandis qu'un autre mécanisme prend le relais jusqu'à 70K. / The work that I present in this thesis is primarily an experimental work carried out in the LAMAp laboratory at the University of Cergy-Pontoise, using the experimental device called FORMOLISM. The main components of this device are: ultra-high vacuum (10-10 mbar), ultra-low temperature (~5 K), atomic jets, TPD mass spectrometry (Thermally Programmed Desorption) and laser spectroscopy using ultraviolet wavelengths around ~200 nm. Thanks to the REMPI-TOF (Resonantly Enhanced Multi-Photon Ionization – Time Of Flight) technique, we have studied i) the nuclear spin conversion of the hydrogen molecule H2 on a porous amorphous water ice surface and ii) the processes of formation of this molecule, which is the most abundant in the interstellar medium, on surfaces simulating interstellar dust grains. The results of this study are of capital interest in astrophysics. Actually, this formation cannot occur in the gas phase but can only be explained by the encounter of two hydrogen atoms on a dust grain in the interstellar medium, the latter playing the role of a catalyst. Different processes are involved in the formation of H2 which require to be identified. With this aim, I present entirely new results on molecular H2 formation on an amorphous silicate surface. I show that the molecule can form in a rovibrationnally excited state of its ground state up to a temperature of about 70 K and that the molecule is released into the gas phase immediately after its formation. These results demonstrate the competition between two mechanisms of formation at very low temperature (<18 K) while another mechanism takes over up to 70 K.

Cette thèse présente le travail réalisé par l'auteur consacréà l'étude de l'influence des vents magnétosphériques des pulsars sur leur environnement. Le problème du vent magnétosphérique des pulsars est étudié dans le contexte des pulsars classiques, qui forment des nébuleuses de pulsar. L'observation de ces nébuleuses fournit des informations importantes sur leurs conditions physiques et dynamiques. Le vent magnétosphérique des pulsars milliseconde est également étudié. La contribution des pulsars millisecondeà l'émission gamma des amas globulaires est étudiée par des simulations numériques.Dans la première partie, les résultats des observations infrarouge du vestige de supernova G21.5-0.9 sont présentées. Les données utilisées comprennent des observations du Very Large Telescope de l'ESO, du télescope Canada-France-Hawaï (CFHT) et du télescope spatial Spitzer. La détection de la nébuleuse compacte autour du pulsar PSR J1833-1034, avec l'instrument CFHT/AOB-KIR (bande K') et la caméra IRAC/Spitzer (toutes les bandes), est présentée. La valeur moyenne de la fraction de polarisation linéaire de l'émission détectée est estiméeà $P_{rm L}^{avg} simeq 0.47$. Une oscillation du vecteur champ électrique dans la nébuleuse compacte peut être observée. Le spectre infrarouge de la nébuleuse compacte est bien décrit par une loi de puissance d'indice $alpha_{rm IR} = 0.7 pm 0.3$, et suggère un aplatissement spectral entre les domaines infrarouge et X. La détection de la raie d'émission [Fe II] à 1.64 $mu$m est présentée. La spectroscopieà moyenne résolution permet d'estimer l'extinction par le milieu interstellaire de l'émission infrarouge de l'objet, ainsi que la vitesse d'expansion de la matière émettant la raie du [Fe II], ce qui conduità une estimation de la distanceà G21.5-0.9 de $3.9 pm 1.2$ kpc.La deuxième partie présente une étude de l'activité magnétosphérique des pulsars milliseconde dans le contexte de l'émission gamma des amas globulaires. Une base de données des caractéristiques d'émission des pulsars milliseconde et des spectres d'éjection des électrons est créée sur la base du modèle pair starved polar cap de la magnétosphère des pulsars. Le concept de facteur de biais est introduit et étudié. Des spectres synthétiques d'amas globulaires sont simulés dans la gamme d'énergie allant du GeV au TeV. Ils consistent en une composante d'émission magnétosphérique des pulsars milliseconde résidant dans l'amas, et une composante Compton inverse résultant de la diffusion des photons ambiants (le champ stellaire des photons provenant des étoiles de l'amas, et le fond diffus cosmologique) par les leptons relativistes diffusant dans l'amas. Enfin, les spectres synthétiques des amas globulaires sont comparés et contrastés avec les observationsà haute et très haute énergie des amas globulaires sélectionnés: Terzan 5 et 47 Tucanae. / This PhD thesis presents the results of the studies on the influence of magnetospheric pulsar winds on the surroundings of these objects. The problem of the magnetospheric pulsar wind is studied in the context of classical pulsars, which power prominent pulsar wind nebulae. Observations of these nebulae yield important information on their physical and dynamical conditions. The magnetospheric winds of millisecond pulsars are also investigated. The contribution of millisecond pulsars to the gamma-ray emission of globular clusters is studied through numerical simulations. In the first part of the thesis, the results of infrared observations of the supernova remnant G21.5-0.9 are presented. The observational material includes data obtained with the ESO Very Large Telescope, the Canada-France-Hawaii Telescope and the Spitzer Space telescope. The detection of the compact nebula around the pulsar PSR J1833-1034, through imaging with both the CFHT/AOB-KIR instrument (K' band) and the IRAC/Spitzer camera (all bands), is reported. The average value of the linear polarisation fraction $P_{rm L}^{avg} simeq 0.47$ of the detected emission is estimated. A swing of the electric field vector across the compact nebula is observed. The infrared spectrum of the compact nebula is best described as a power law of index $alpha_{rm IR} = 0.7 pm 0.3$, and suggests its flattening between the infrared and X-ray bands. The detection of [Fe II] 1.64 $mu$m line emitting material is reported. Through medium resolution spectroscopy the infrared interstellar extinction to the object is estimated, and also the expansion velocity of the iron-line emitting material is determined, which in turn leads to estimating the distance of $d = 3.9 pm 1.2$ kpc to G21.5-0.9. The second part presents a study of the magnetospheric activity of millisecond pulsars in the context of the gamma-ray emission of globular clusters. Based on the pair starved polar cap model of the pulsar magnetosphere the database of the millisecond pulsar emission characteristics and the electron ejection spectra is created. The modelled electron ejection spectra are single-peaked for mildly inclined and fast rotating pulsars, while double-peaked for slowly rotating pulsars. The concept of the bias factor is introduced and studied. Synthetic spectra of globular clusters, stretching from MeV up to TeV energies, are simulated. They consist of the magnetospheric contribution from the millisecond pulsar population residing in the cluster, and an inverse Compton scattering (ICS) component resulting from up-scattering of the ambient photon fields (cosmic microwave background and optical photons from stellar population in the cluster) on the relativistic electrons diffusing through the cluster. The spectral characteristics of the ICS component depends on the composition of the ambient photon fields and also on the magnitude of the cluster magnetic field $B_{rm GC}$. For low $B_{rm GC} sim 1 mu$G the spectra are double-peaked. For the high $B_{rm GC} gtrsim 10 mu$G the ICS spectra are single-peaked. The level of ICS emission increases with the increase of $B_{rm GC}$, but it saturates for $B_{rm GC} sim 10 ~mu$G. Finally, the simulated synthetic spectra of globular clusters are confronted with the existing gamma-ray data for selected clusters: Terzan 5 and 47 Tucanae.

In this thesis, we aim to further elucidate the phenomenon of galaxy evolution in the environment of galaxy clusters using the methodology of numerical simulations. For that, we have developed hydrodynamic models in which idealized gas-rich galaxies move within the ICM of idealized galaxy clusters, allowing us to probe in a detailed and controlled manner their evolution in this extreme environment. The main code used in our simulations is RAMSES, and our results concern the changes in gas composition, star formation rate, luminosity and color of infalling galaxies. Additionally to processes taking place inside the galaxies themselves, we have also described the dynamics of the gas that is stripped from those galaxies with unprecedented resolution for simulations of this nature (122 pc in a box including an entire 1e14 Msun cluster), finding that clumps of molecular gas are formed within the tails of ram pressure stripped galaxies, which proceed to live in isolation within the ICM of a galaxy cluster for up to 300 Myr. Those molecular clumps possibly represent a new class of objects; similar objects have been observed in both galaxy clusters and groups, but no comprehensive description of them has been given until now. We additionally create a hydrodynamic model for the A901/2 multi-cluster system, and correlate the gas conditions in this model to the locations of a sample of candidate jellyfish galaxies in the system; this has allowed us to infer a possible mechanism for the generation of jellyfish morphologies in galaxy cluster collisions in general. / Nesta tese, nós visamos a contribuir para o entendimento do fenômeno da evolução de galáxias no ambiente de aglomerados de galáxias usando a metodologia de simulações numéricas. Para isso, desenvolvemos modelos hidrodinâmicos nos quais galáxias idealizadas ricas em gás movem-se em meio ao gás difuso de aglomerados de galáxias idealizados, permitindo um estudo detalhado e controlado da evolução destas galáxias neste ambiente extremo. O principal código usado em nossas simulações é o RAMSES, e nossos resultados tratam das mudanças em composição do gás, taxa de formação estelar, luminosidade e cor de galáxias caindo em aglomerados. Adicionalmente a processos acontecendo dentro das próprias galáxias, nós também descrevemos a dinâmica do gás que é varrido dessas galáxias com resolução sem precedentes para simulações dessa natureza (122 pc em uma caixa incluindo um aglomerado de 1e14 Msun inteiro), encontrando que aglomerados de gás molecular são formados nas caudas de galáxias que passaram por varrimento de gás por pressão de arraste, aglomerados estes que procedem a viver em isolamento em meio ao gás difuso de um aglomerado de galáxias por até 300 Myr. Esses aglomerados moleculares possivelmente representam uma nova classe de objetos; objetos similares foram previamente observados tanto em aglomerados quanto em grupos de galáxias, mas um tratamento compreensivo deles não foi apresentado até agora. Nós adicionalmente criamos um modelo hidrodinâmico para o sistema multi-aglomerado A901/2, e correlacionamos as condições do gás nesse modelo com a localização de uma amostra de galáxias jellyfish nesse sistema; isso nos permitiu inferir um possível mecanismo para a geração de morfologias jellyfish em colisões de aglomerados de galáxias em geral.

In this thesis, we aim to further elucidate the phenomenon of galaxy evolution in the environment of galaxy clusters using the methodology of numerical simulations. For that, we have developed hydrodynamic models in which idealized gas-rich galaxies move within the ICM of idealized galaxy clusters, allowing us to probe in a detailed and controlled manner their evolution in this extreme environment. The main code used in our simulations is RAMSES, and our results concern the changes in gas composition, star formation rate, luminosity and color of infalling galaxies. Additionally to processes taking place inside the galaxies themselves, we have also described the dynamics of the gas that is stripped from those galaxies with unprecedented resolution for simulations of this nature (122 pc in a box including an entire 1e14 Msun cluster), finding that clumps of molecular gas are formed within the tails of ram pressure stripped galaxies, which proceed to live in isolation within the ICM of a galaxy cluster for up to 300 Myr. Those molecular clumps possibly represent a new class of objects; similar objects have been observed in both galaxy clusters and groups, but no comprehensive description of them has been given until now. We additionally create a hydrodynamic model for the A901/2 multi-cluster system, and correlate the gas conditions in this model to the locations of a sample of candidate jellyfish galaxies in the system; this has allowed us to infer a possible mechanism for the generation of jellyfish morphologies in galaxy cluster collisions in general. / Nesta tese, nós visamos a contribuir para o entendimento do fenômeno da evolução de galáxias no ambiente de aglomerados de galáxias usando a metodologia de simulações numéricas. Para isso, desenvolvemos modelos hidrodinâmicos nos quais galáxias idealizadas ricas em gás movem-se em meio ao gás difuso de aglomerados de galáxias idealizados, permitindo um estudo detalhado e controlado da evolução destas galáxias neste ambiente extremo. O principal código usado em nossas simulações é o RAMSES, e nossos resultados tratam das mudanças em composição do gás, taxa de formação estelar, luminosidade e cor de galáxias caindo em aglomerados. Adicionalmente a processos acontecendo dentro das próprias galáxias, nós também descrevemos a dinâmica do gás que é varrido dessas galáxias com resolução sem precedentes para simulações dessa natureza (122 pc em uma caixa incluindo um aglomerado de 1e14 Msun inteiro), encontrando que aglomerados de gás molecular são formados nas caudas de galáxias que passaram por varrimento de gás por pressão de arraste, aglomerados estes que procedem a viver em isolamento em meio ao gás difuso de um aglomerado de galáxias por até 300 Myr. Esses aglomerados moleculares possivelmente representam uma nova classe de objetos; objetos similares foram previamente observados tanto em aglomerados quanto em grupos de galáxias, mas um tratamento compreensivo deles não foi apresentado até agora. Nós adicionalmente criamos um modelo hidrodinâmico para o sistema multi-aglomerado A901/2, e correlacionamos as condições do gás nesse modelo com a localização de uma amostra de galáxias jellyfish nesse sistema; isso nos permitiu inferir um possível mecanismo para a geração de morfologias jellyfish em colisões de aglomerados de galáxias em geral.

We show some preliminary 10-37 micron high-resolution spectra taken with the Spitzer Space Telescope in 2008-9 of Mira variables distributed across the M, S and C chemical subclasses. Our entire Spitzer sample of 25 galactic Miras was observed from two to several times during this observing campaign and all have simultaneously measured near-infrared interferometric diameters acquired using the Palomar Testbed Interferometer. Because our sources are very bright for Spitzer IRS (typically 5-100 Janskys), we have excellent signal to noise and for many sources see marked changes in overall flux levels as a function of phase. Further, we are able to identify many strong emission lines and emission features due to silicate and carbon dusts and molecular constituents. We introduce the sample and the design of our experiment, discuss the data reduction required for such bright sources using Spitzer, show several examples of spectra with phase and discuss some preliminary findings. Finally, we discuss future steps for Paper II, to be presented later in the year.

We present new radio/millimeter measurements of the hot magnetic star HR 5907 obtained with the VLA and ALMA interferometers. We find that HR 5907 is the most radio luminous early type star in the cm–mm band among those presently known. Its multi-wavelength radio light curves are strongly variable with an amplitude that increases with radio frequency. The radio emission can be explained by the populations of the non-thermal electrons accelerated in the current sheets on the outer border of the magnetosphere of this fast-rotating magnetic star. We classify HR 5907 as another member of the growing class of strongly magnetic fast-rotating hot stars where the gyro-synchrotron emission mechanism efficiently operates in their magnetospheres. The new radio observations of HR 5907 are combined with archival X-ray data to study the physical condition of its magnetosphere. The X-ray spectra of HR 5907 show tentative evidence for the presence of non-thermal spectral component. We suggest that non-thermal X-rays originate a stellar X-ray aurora due to streams of non-thermal electrons impacting on the stellar surface. Taking advantage of the relation between the spectral indices of the X-ray power-law spectrum and the non-thermal electron energy distributions, we perform 3-D modelling of the radio emission for HR 5907. The wavelength-dependent radio light curves probe magnetospheric layers at different heights above the stellar surface. A detailed comparison between simulated and observed radio light curves leads us to conclude that the stellar magnetic field of HR 5907 is likely non-dipolar, providing further indirect evidence of the complex magnetic field topology of HR 5907.

AH Cep and CW Cep are both early B-type binaries with short orbital periods of 1.8 days and 2.7 days, respectively. All four components are B0.5V types. The binaries are also double-lined spectroscopic and eclipsing. Consequently, solutions for orbital and stellar parameters make the pair of binaries ideal targets for a study of the colliding winds between two B stars. Chandra ACIS-I observations were obtained to determine X-ray luminosities. AH Cep was detected with an unabsorbed X-ray luminosity at a 90% confidence interval of erg s−1, or , relative to the combined Bolometric luminosities of the two components. While formally consistent with expectations for embedded wind shocks, or binary wind collision, the near-twin system of CW Cep was a surprising nondetection. For CW Cep, an upper limit was determined with , again for the combined components. One difference between these two systems is that AH Cep is part of a multiple system. The X-rays from AH Cep may not arise from standard wind shocks nor wind collision, but perhaps instead from magnetism in any one of the four components of the system. The possibility could be tested by searching for cyclic X-ray variability in AH Cep on the short orbital period of the inner B stars.

The influence of macroclumps for free–free spectral energy distributions (SEDs) of ionized winds is considered. The goal is to emphasize distinctions between microclumping and macroclumping effects. Microclumping can alter SED slopes and flux levels if the volume filling factor of the clumps varies with radius; however, the modifications are independent of the clump geometry. To what extent does macroclumping alter SED slopes and flux levels? In addressing the question, two specific types of macroclump geometries are explored: shell fragments (pancake-shaped) and spherical clumps. Analytic and semi-analytic results are derived in the limiting case that clumps never obscure one another. Numerical calculations based on a porosity formalism is used when clumps do overlap. Under the assumptions of a constant expansion, isothermal, and fixed ionization wind, the fragment model leads to results that are essentially identical to the microclumping result. Mass-loss rate determinations are not affected by porosity effects for shell fragments. By contrast, spherical clumps can lead to a reduction in long-wavelength fluxes, but the reductions are only significant for extreme volume filling factors.

The blue hypergiant Cyg OB2 12 (B3Ia+) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si xivand Mg xii. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere or in a colliding wind zone between binary components. The observed X-ray spectra are well-fitted by thermal plasma models, with average temperatures in excess of 10 MK. The wind speed in Cyg OB2 12 is not high enough to power such high temperatures, but the collision of two winds in a binary system can be sufficient. We used archival data to investigate the X-ray properties of other blue hypergiants. In general, stars of this class are not detected as X-ray sources. We suggest that our new Chandra observations of Cyg OB2 12 can be best explained if Cyg OB2 12 is a colliding wind binary possessing a late O-type companion. This makes Cyg OB2 12 only the second binary system among the 16 known Galactic hypergiants. This low binary fraction indicates that the blue hypergiants are likely products of massive binary evolution during which they either accreted a significant amount of mass or already merged with their companions.

Context. The structure of the inner parts of Be star disks (≲ 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided. Aims. We test the VDD model predictions for the extended parts of a sample of six Be disks that have been observed in the radio to address the question of whether the observed turndown in the spectral energy distribution (SED) can be explained in the framework of the VDD model, including recent theoretical development for truncated Be disks in binary systems. Methods. We combine new multi-wavelength radio observations from the Karl. G. Jansky Very Large Array (JVLA) and Atacama Pathfinder Experiment (APEX) with previously published radio data and archival SED measurements at ultraviolet, visual, and infrared wavelengths. The density structure of the disks, including their outer parts, is constrained by radiative transfer modeling of the observed spectrum using VDD model predictions. In the VDD model we include the presumed effects of possible tidal influence from faint binary companions. Results. For 5 out of 6 studied stars, the observed SED shows strong signs of SED turndown between far-IR and radio wavelengths. A VDD model that extends to large distances closely reproduces the observed SEDs up to far IR wavelengths, but fails to reproduce the radio SED. Using a truncated VDD model improves the fit, leading to a successful explanation of the SED turndown observed for the stars in our sample. The slope of the observed SEDs in the radio is however not well reproduced by disks that are simply cut off at a certain distance. Rather, some matter seems to extend beyond the truncation radius, where it still contributes to the observed SEDs, making the spectral slope in the radio shallower. This finding is in agreement with our current understanding of binary truncation from hydrodynamical simulations, in which the disk does extend past the truncation radius. Therefore, the most probable cause for the SED turndown is the presence of binary companions that remain undetected for most of our sources.