Circular polarization from the Zeeman effect is difficult to detect whenever the ratio of the magnetic field strength to the linewidth is small, as might be expected in the winds of hot stars. However, globally structured fields, such as radially swept fields, do present a characteristically complex Zeeman signature that can be distinguished from noise even when small, because of its telltale features that are antisymmetric about the line. If the emission lines are skewed blueward, a signature of photospheric occultation of the redshifted hemisphere, we find that occultation will also reduce the detectability of the Zeeman effect on the red side of the line, further limiting our ability to detect weak magnetic fields in hypersonic winds. Hence, as instrumental precision improves sufficiently, symmetric emission lines will present advantages over lines skewed blueward by occultation, when seeking a Zeeman signal.

Binary mass transfer is a common phenomenon is stellar astrophysics. If the mass transfer proceeds on dynamical timescale, the binary can undergo a catastrophic interaction accompanied by tremendous loss of mass, angular momentum, and energy. This so-called common envelope evolution phase is a crucial step in the formation of close binaries composed of compact objects (white dwarfs, neutron stars, black holes), which includes progenitors of gravitational wave sources de- tected by LIGO. By improving existing models of binary mass transfer we can correct the predictions of common envelope evolution and constraint the rates of close binaries composed of compact objects. In this work, we introduce new model of binary mass transfer. We will treat the mass transfer as a special case of stellar wind. We will rely on the assumption that the Roche potential sets up a de Laval nozzle around the first Lagrange point. The mass is then transferred through the nozzle. Our binary mass transfer model predicts mass transfer rates in the same order of magnitude as the standard models which use the Bernoulli's law. But the advantage of our model is that it is extendable to account for radiation.

Massive binary evolution is crucial for our understanding of many pheno- mena in the Universe, such as high-mass X-ray binaries or the formation of compact systems emitting gravitational waves. In this work, we study the loss of angular momentum from binary systems caused by radiation driven stellar winds, which are characteristic for hot, massive stars. Calculating numerically ballistic trajectories of particles ejected from the binary surface, we establish the average specific angular momentum loss as a function of the system's mass ratio for binaries in semidetached and contact stages. We initiate the outflow on the Roche lobes or even on further equipotentials of the Roche potential in case of over-contact systems. Moreover, we implement two models of the radiation driven wind. Firstly, we eject particles from the surface of the binary with a non-zero initial velocity, but we then let them evolve only under the influence of the system's gravity. In the second model, we develop a simple method for computing the radiative acceleration due to the radiation pressure from the bi- nary surface. Our results can be used in further calculations of the evolution of massive binary systems.

Esta tesis doctoral por compendio de artículos está formada por tres análisis en los que estudiamos observaciones tomadas con el telescopio XMM-Newton de tres fuentes diferentes: La fuente 4U0114+65 es uno de los púlsares más lentos conocidos hasta el momento. Está formado por una donante de alta masa de tipo espectral B1Ia y una NS que la orbita con un periodo de 11.6 d. La NS gira sobre su eje con un periodo de ~ 9350 s. Esta fuente podría ser un magnetar (NS con un campo magnético muy intenso, incluso para una NS). En este trabajo presentamos el análisis de una observación en periodo propietario realizada con el satélite XMM-Newton durante 49 ks, donde hemos estudiado el proceso de acreción, las propiedades del viento estelar y la naturaleza de los pulsos de rayos X. Cen X-3 es un sistema binario compacto de rayos X de alta masa. La acreción sobre el objeto compacto, una NS en este caso, tiene lugar mediante disco de acreción. En este trabajo hemos analizado dos observaciones llevadas a cabo con el telescopio XMM-Newton. Una de ellas tuvo lugar en el año 2001, durante las fases orbitales ∅= 0.0 − 0.37. Esta observación fue tomada durante la salida del eclipse del objeto compacto, cuando la fuente se encontraba en un estado súper-orbital hard-low, hard porque la emisión de rayos X es muy energética y low porque la intensidad es baja. La segunda observación tuvo lugar en el año 2006, durante las fases orbitales ∅= 0.35 − 0.8. En este caso la fuente se encontraba en un estado súper-orbital soft-high, es decir, la luz emitida no es tan energética como en la primera observación pero su intensidad es mayor. Por último, presentamos un análisis de la primera observación tomada con el observatorio XMM-Newton del sistema eclipsante HMXRB XTE J1855−026. La observación tuvo lugar totalmente durante el eclipse de la NS, cubriendo las fases orbitales ∅= 0.00 − 0.11. Hemos comparado nuestro análisis de la fuente en eclipse con uno previo realizado con Suzaku en las fases orbitales previas al eclipse y hemos estudiado el viento estelar retroiluminado de la donante tipo B0I.

A number of strong infrared forbidden lines have been observed in several evolved Wolf–Rayet (WR) star winds, and these are important for deriving metal abundances and testing stellar evolution models. In addition, because these optically thin lines form at large radius in the wind, their resolved profiles carry an imprint of the asymptotic structure of the wind flow. This work presents model forbidden line profile shapes formed in axisymmetric winds. It is well known that an optically thin emission line formed in a spherical wind expanding at constant velocity yields a flat-topped emission profile shape. Simulated forbidden lines are produced for a model stellar wind with an axisymmetric density distribution that treats the latitudinal ionization self-consistently and examines the influence of the ion stage on the profile shape. The resulting line profiles are symmetric about line centre. Within a given atomic species, profile shapes can vary between centrally peaked, doubly peaked, and approximately flat-topped in appearance depending on the ion stage (relative to the dominant ion) and viewing inclination. Although application to WR star winds is emphasized, the concepts are also relevant to other classes of hot stars such as luminous blue variables and Be/B[e] stars.

This paper examines line profile evolution due to the linear expansion of circumstellar material obsverved during a microlensing event. This work extends our previous papers on emission line profile evolution from radial and azimuthal flow during point mass lens events and fold caustic crossings. Both “flavours” of microlensing were shown to provide effective diagnostics of bulk motion in circumstellar envelopes. In this work a different genre of flow is studied, namely linear homologous expansion, for both point mass lenses and fold caustic crossings. Linear expansion is of particular relevance to the effects of microlensing on supernovae at cosmological distances. We derive line profiles and equivalent widths for the illustrative cases of pure resonance and pure recombination lines, modelled under the Sobolev approximation. The efficacy of microlensing as a diagnostic probe of the stellar environs is demonstrated and discussed

The Chandra and XMM-Newton X-ray telescopes have led to numerous advances in the study and understanding of astrophysical X-ray sources. Particularly important has been the much increased spectral resolution of modern X-ray instrumentation. Wind-broadened emission lines have been spectroscopically resolved for many massive stars. This contribution reviews approaches to the modeling of X-ray emission line profile shapes from single stars, including smooth winds, winds with clumping, optically thin versus thick lines, and the effect of a radius-dependent photoabsorption coefficient.

Stellar winds play an important role for the evolution of massive stars and their cosmic environment. Multiple lines of evidence, coming from spectroscopy, polarimetry, variability, stellar ejecta, and hydrodynamic modeling, suggest that stellar winds are non-stationary and inhomogeneous. This is referred to as 'wind clumping'. The urgent need to understand this phenomenon is boosted by its far-reaching implications. Most importantly, all techniques to derive empirical mass-loss rates are more or less corrupted by wind clumping. Consequently, mass-loss rates are extremely uncertain. Within their range of uncertainty, completely different scenarios for the evolution of massive stars are obtained. Settling these questions for Galactic OB, LBV and Wolf-Rayet stars is prerequisite to understanding stellar clusters and galaxies, or predicting the properties of first-generation stars. In order to develop a consistent picture and understanding of clumped stellar winds, an international workshop on 'Clumping in Hot Star Winds' was held in Potsdam, Germany, from 18. - 22. June 2007. About 60 participants, comprising almost all leading experts in the field, gathered for one week of extensive exchange and discussion. The Scientific Organizing Committee (SOC) included John Brown (Glasgow), Joseph Cassinelli (Madison), Paul Crowther (Sheffield), Alex Fullerton (Baltimore), Wolf-Rainer Hamann (Potsdam, chair), Anthony Moffat (Montreal), Stan Owocki (Newark), and Joachim Puls (Munich). These proceedings contain the invited and contributed talks presented at the workshop, and document the extensive discussions.

Mass loss, in the form of slow stellar winds, is a decisive factor for the evolution of cool luminous giants, eventually turning them into white dwarfs. These dense outflows are also a key factor in the enrichment of the interstellar medium with newly produced elements from the interior of these stars. There are strong indications that these winds are accelerated by radiation pressure on dust grains, but the actual grain species responsible for driving the outflows in M-type Asymptotic Giant Branch stars are still a matter of debate. Observations of dust features in the circumstellar environment of these stars suggest that magnesium-iron silicates are possible wind-drivers. However, the optical properties of these silicate grains are strongly influenced by the Fe-content. Fe-bearing condensates heat up strongly when interacting with the radiation field and therefore cannot form close enough to the star to trigger outflows. Fe-free condensates, on the other hand, have a low absorption cross-section at near-IR wavelengths where AGB stars emit most of their flux.  To solve this conundrum, it has been suggested that winds of M-type AGB stars may be driven by photon scattering on Fe-free silicate grains with sizes comparable to the wavelength of the flux maximum, rather than by true absorption. In this thesis we investigate dynamical models of M-type AGB stars, using Fe-free silicates as the wind-driving dust species. According to our findings these models produce both dynamic and photometric properties consistent with observations. Especially noteworthy are the large photometric variations in the visual band during a pulsation cycle, seen both in the observed and synthetic fluxes. A closer examination of the models reveals that these variations are caused by changes in the molecular layers, and not by changes in the dust. This is a strong indication that stellar winds of M-type AGB stars are driven by dust materials that are very transparent in the visual and near-infrared wavelength regions, otherwise these molecular effects would not be visible.

L'objectif de cette thèse est de comprendre la structure des binaires gamma, binaires à collision de vents composées d'une étoile massive et d'un pulsar jeune. Ces binaires possèdent probablement une structure similaire aux binaires à collision de vents composées de deux étoiles massives, avec des particularités liées à la nature relativiste du vent de pulsar. L'interaction de deux vents supersoniques d'étoiles massives crée une structure choquée qui présente des signatures observationnelles du domaine radio aux rayons X. Plusieurs instabilités ainsi que le mouvement orbital des étoiles influent sur la structure choquée. Afin de comprendre leur impact, j'ai effectué des simulations à haute résolution de binaires à collision de vents à l'aide du code hydrodynamique RAMSES. Ces simulations sont numériquement coûteuses à réaliser, surtout lorsque un des vents domine fortement l'autre. A petite échelle, les simulations soulignent l'importance de l'instabilité de couche mince non-linéaire dans les collisions isothermes alors que l'instabilité de Kelvin-Helmholtz peut fortement modifier la structure choquée dans une collision adiabatique. A plus grande échelle, cette instabilité peut parfois détruire la structure spirale à laquelle on s'attend si la différence de vitesse entre les vents est trop importante. WR 104 est une binaire dont on observe la structure spirale grâce à l'émission de poussières. Les simulations de ce système montrent un bon accord avec la structure observée et indiquent que des processus de refroidissement du gaz sont nécessaires à la formation de poussières. Pour modéliser les vents de pulsar dans les binaires gamma, RAMSES a été étendu à l'hydrodynamique relativiste. J'utilise ce nouveau code pour réaliser des simulations préliminaires de binaires gamma. Elles montrent effectivement une structure similaire aux binaires stellaires, avec de légères corrections relativistes . Ce code est adapté à l'étude de divers systèmes astrophysiques tels que les jets relativistes, les sursauts gamma ou les nébuleuses de pulsar et fera partie de la prochaine version de RAMSES qui sera rendue publique. / The aim of this thesis is to understand the structure of colliding wind binaries composed of a massive star and a young pulsar, called gamma-ray binaries. They are expected to display a similar structure to colliding wind binaries composed of massive stars, with some particularities due to the relativistic nature of the pulsar wind. The interaction of the supersonic winds from massive stars creates a shocked structure with observational signatures from the radio domain to the X-rays. The structure is affected by various instabilities and by the orbital motion of the stars. To understand their impact, I carried out high resolution simulations of colliding wind binaries with the hydrodynamical code RAMSES. They are computationally demanding, especially when one of the winds strongly dominates the other one. Small scale simulations highlight the importance of the Non-linear Thin Shell Instability in isothermal collisions while the Kelvin-Helmholtz instability may strongly impact the dynamics of adiabatic collisions. I found that, at larger scales, this instability can destroy the expected large scale spiral structure when there is an important velocity gradient between the winds. WR 104 is a system that displays a spiral structure with important dust emission. The simulation of this system shows a good agreement with the observed structure and indicates cooling processes are necessary to enable dust formation. To model the pulsar wind in gamma-ray binaries, an extension of RAMSES has been developed, that incorporates relativistic hydrodynamics. I used this new relativistic code to perform preliminary simulations of gamma-ray binaries. They display a similar structure to colliding wind binaries with small relativistic corrections. We expect to use this code to perform large scale simulations of gamma-ray binaries. It will be part of the next public release of RAMSES and is suited for the study of many astrophysical problems such as relativistic jets, pulsar wind nebulae or gamma-ray bursts.