<p>One of the most fundamental problems in theories of planet formation in protoplanetary disks is planetary migration that arises from resonant, tidal interactions of forming planets with the natal disks. This rapid inward migration, also known as type I migration, leads to the well-known problem that its timescale is about two orders of magnitude shorter than the typical disk lifetime, so that (proto)planets plunge into the host stars within the disk lifetime. This provides a huge hurdle for understanding the statistical properties of observed extra solar planets that now amount to more than 700.</p> <p>In this thesis, we focus on one of the most general properties of protoplanetary disks - inhomogeneities. A large amount of theoretical and observational work currently suggests that protoplanetary disks are most likely to possess several kinds of inhomogeneities. Planetary migration is highly sensitive to the disk properties such as the surface density and temperature of disks, and the sensitivity leads to the formation of trapping sites for rapid type I migration at disk inhomogeneities. These local sites capturing planets undergoing migration are referred to as planet traps. We perform both analytical and numerical studies for exploring formation mechanisms of planet traps at disk inhomogeneities and their consequences for the formation and evolution of planetary systems. We focus on three kinds of the disk inhomogeneities: dead zones, ice lines, and transitions of heat sources in protoplanetary disks we refer to as heat transitions. Dead zones are an inevitable consequence of disk turbulence originating from magnetorotational instabilities (MRIs) that take place in (partially) ionized disks threaded by weak magnetic fields. One of the fundamental properties of the dead zone is a low level of turbulence there, which is the outcome of the high density, preventing the region from being ionized due to X-rays from the central stars and cosmic rays. Ice lines are formed due to low disk temperatures which lead to condensation of specific molecules there. Heat transitions arise as a consequence of the switching of the dominant heating process from viscous heating to stellar irradiation as the distance to the host stars increases.</p> <p>We summarize our major findings. 1) rapid dust settling arising in dead zones leaves a dusty wall at the outer edge of the dead zones beyond which the disks are quite turbulent, so that dust is fully mixed with the gas. Efficient heating of the wall by stellar irradiation and the subsequent backward heating of the dead zones by the wall result in a positive temperature gradient in the dead zones. This inversion in the temperature profiles leads to outward migration there. 2) Any protoplanetary disk is likely to possess up to three types of planet traps that are specified by characteristic disk radii (dead zone, ice line and heat transition traps). Disk evolution, driven by disk viscosity, lowers both the accretion rate and surface density of gas and moves traps inward at different rates. This suggests that the interactions of (proto)planets captured at different traps play the dominant role in constructing planetary system architectures. Furthermore, the distribution of planet traps depends largely on stellar masses and accretion rates, so that they are one of the principle parameters for regulating the (initial) scale of planetary systems. 3) Both multiplicity and mobility of planet traps are crucial for understanding the statistical properties of observed extra solar planets. For instance, the mass-period relation - observational manifestation that planetary mass is an increasing function of orbital periods - can be understood by constructing and following evolutionary tracks of accreting planets in planet traps. These three contribution are new results in the field.</p> / Doctor of Philosophy (PhD)

This thesis is concerned with various aspects of the detection and characterisation of transiting extra-solar planets. The noise properties of photometric data from SuperWASP, a wide-field survey instrument designed to detect exoplanets, are investigated. There has been a large shortfall in the number of planets such transit surveys have detected, compared to previous predictions of the planet catch. It has been suggested that correlated, or red, noise in the photometry is responsible for this; here it is confirmed that red noise is present in the SuperWASP photometry, and its effects on planet discovery are quantified. Examples are given of follow-up photometry of candidate transiting planets, confirming that modestly-sized telescopes can rule out some candidates photometrically. A Markov-chain Monte Carlo code is developed to fit transit lightcurves and determine the depth of such lightcurves in different passbands. Tests of this code with transit data of WASP-3 b are reported. The results of a search for additional transiting planets in known transiting planetary systems are presented. SuperWASP photometry of 24 such systems is searched for additional transits. No further planets are discovered, but a strong periodic signal is detected in the photometry of WASP-10. This is ascribed to stellar rotational variation, the period of which is determined to be 11.91 ± 0.05 days. Monte Carlo modelling is performed to quantify the ability of SuperWASP to detect additional transiting planets; it is determined that there is a good (> 50 per cent) chance of detecting additional, Saturn-sized planets in P ~ 10 day orbits. Finally, the first-ever attempt to detect the secondary eclipse of a transiting extra-solar planet at radio wavelengths is made. Although no eclipse is conclusively detected, upper limits to the flux density from HD 189733 b are established, and compared to theoretical predictions of the flux due to electron-cyclotron maser emission.

This dissertation treats the theory and practice of C. S. Lewis's theological imagination, focussing upon the imaginative use he made of his professional expertise in medieval and renaissance literature. Its approach is principally expository rather than an evaluative. Chapter One outlines the centrality of the imagination to a proper understanding of Lewis's works. Chapter Two examines Lewis's own theory of imagination and surveys how he practised it as a literary critic. We compare and contrast Lewis's theory and practice of imagination with that of his friend, the theologian, Austin Faffer. Chapter Three looks in more detail at Lewis's imaginative practice, in particular his fascination with the images supplied by the seven planets of the Ptolemaic cosmos, which he termed 'spiritual symbols of permanent value'. We analyse what he meant by 'sprit' and 'symbol'. Chapter Four introduces the main argument of the dissertation namely that these seven spiritual symbols structure the works for which Lewis is best known, the seven 'Chronicles of Narnia'. We claim to have uncovered the governing imaginative blueprint of the septet. We address Lewis's capacity for and interest in secrecy and consider why this planetary theme has remained hitherto undetected. In Chapters Five to Eleven we take the seven planets in turn and trace the use Lewis made of them through out his writings. We analyse the planetary symbolism undergirding each Chronicle and conclude each chapter with an exegesis of the Christological message of each book so understood. Chapter Twelve examines factors which motivated Lewis to focus his imaginative energies upon Ptolemaic cosmology and suggests one particular occasioning factor behind the composition of the Chronicles. In addition, we consider theological and pedagogical reasons why he kept silent about the planetary theme. We conclude by indicating certain consequences that our argument has for future readings of these seven works.

We report ALMA Cycle 2 observations of 230 GHz (1.3 mm) dust continuum emission, and (CO)-C-12, (CO)-C-13, and (CO)-O-18 J = 2-1 line emission, from the Upper Scorpius transitional disk [PZ99] J160421.7-213028, with an angular resolution of similar to 0''.25 (35 au). Armed with these data and existing H-band scattered light observations, we measure the size and depth of the disk's central cavity, and the sharpness of its outer edge, in three components: sub-mu m-sized "small" dust traced by scattered light, millimeter-sized "big" dust traced by the millimeter continuum, and gas traced by line emission. Both dust populations feature a cavity of radius similar to 70 au that is depleted by factors of at least 1000 relative to the dust density just outside. The millimeter continuum data are well explained by a cavity with a sharp edge. Scattered light observations can be fitted with a cavity in small dust that has either a sharp edge at 60 au, or an edge that transitions smoothly over an annular width of 10 au near 60 au. In gas, the data are consistent with a cavity that is smaller, about 15 au in radius, and whose surface density at 15 au is 10(3 +/- 1) times smaller than the surface density at 70 au; the gas density grades smoothly between these two radii. The CO isotopologue observations rule out a sharp drop in gas surface density at 30 au or a double-drop model, as found by previous modeling. Future observations are needed to assess the nature of these gas and dust cavities (e.g., whether they are opened by multiple as-yet-unseen planets or photoevaporation).

High-contrast imaging instruments such as GPI and SPHERE are discovering gap structures in protoplanetary disks at an ever faster pace. Some of these gaps may be opened by planets forming in the disks. In order to constrain planet formation models using disk observations, it is crucial to find a robust way to quantitatively back out the properties of the gap-opening planets, in particular their masses, from the observed gap properties, such as their depths and widths. Combining 2D and 3D hydrodynamics simulations with 3D radiative transfer simulations, we investigate the morphology of planet-opened gaps in near-infrared scattered-light images. Quantitatively, we obtain correlations that directly link intrinsic gap depths and widths in the gas surface density to observed depths and widths in images of disks at modest inclinations under finite angular resolution. Subsequently, the properties of the surface density gaps enable us to derive the disk scale height at the location of the gap h, and to constrain the quantity M-p(2)/alpha, where Mp is the mass of the gap-opening planet and a characterizes the viscosity in the gap. As examples, we examine the gaps recently imaged by VLT/SPHERE, Gemini/GPI, and Subaru/HiCIAO in HD 97048, TW Hya, HD 169142, LkCa. 15, and RX J1615.3-3255. Scale heights of the disks and possible masses of the gap-opening planets are derived assuming each gap is opened by a single planet. Assuming a = 10(-3), the derived planet masses in all cases are roughly between 0.1 and 1M(J).

Stars form via the gravitational collapse of molecular clouds during which time the protostellar object contracts by over seven orders of magnitude. If all the angular momentum present in the natal cloud was conserved during collapse, stars would approach rotational velocities rapid enough to tear themselves apart within just a few Myr. In contrast to this, observations of pre-main sequence rotation rates are relatively slow (∼ 1 − 15 days) indicating that significant quantities of angular momentum must be removed from the star. I use observations of fully convective pre-main sequence stars in two well-studied, nearby regions of star formation (namely the Orion Nebula Cluster and Taurus-Auriga) to determine the removal rate of stellar angular momentum. I find the accretion disc-hosting stars to be rotating at a slower rate and contain less specific angular momentum than the disc-less stars. I interpret this as indicating a period of accretion disc-regulated angular momentum evolution followed by near-constant rotational evolution following disc dispersal. Furthermore, assuming that the age spread inferred from the Hertzsprung-Russell diagram constructed for the star forming region is real, I find that the removal rate of angular momentum during the accretion-disc hosting phase to be more rapid than that expected from simple disc-locking theory whereby contraction occurs at a fixed rotation period. This indicates a more efficient process of angular momentum removal must operate, most likely in the form of an accretion-driven stellar wind or outflow emanating from the star-disc interaction. The initial circumstellar envelope that surrounds a protostellar object during the earliest stages of star formation is rotationally flattened into a disc as the star contracts. An effective viscosity, present within the disc, enables the disc to evolve: mass accretes inwards through the disc and onto the star while momentum migrates outwards, forcing the outer regions of the disc to expand. I used spatially resolved submillimetre detections of the dust and gas components of protoplanetary discs, gathered from the literature, to measure the radial extent of discs around low-mass pre-main sequence stars of ∼ 1−10 Myr and probe their viscous evolution. I find no clear observational evidence for the radial expansion of the dust component. However, I find tentative evidence for the expansion ofthe gas component. This suggests that the evolution of the gas and dust components of protoplanetary discs are likely governed by different astrophysical processes. Observations of jets and outflows emanating from protostars and pre-main sequence stars highlight that it may also be possible to remove angular momentum from the circumstellar material. Using the sample of spatially resolved protoplanetary discs, I find no evidence for angular momentum removal during disc evolution. I also use the spatially resolved debris discs from the Submillimetre Common-User Bolometer Array-2 Observations of Nearby Stars survey to constrain the amount of angular momentum retained within planetary systems. This sample is compared to the protoplanetary disc angular momenta and to the angular momentum contained within pre-stellar cores. I find that significant quantities of angular momentum must be removed during disc formation and disc dispersal. This likely occurs via magnetic braking during the formation of the disc, via the launching of a disc or photo-evaporative wind, and/or via ejection of planetary material following dynamical interactions.

O Sistema Solar é um dos temas da Astronomia mais abordados em sala de aula por professores de Ciências. Reconhecendo sua importância, nesta pesquisa buscamos investigar uma proposta de ensino-aprendizagem no tema \"A forma e os movimentos dos planetas no Sistema Solar\", que teve como eixo central a relação entre a observação cotidiana e os modelos científicos atualmente aceitos. Para ajudar na construção dessa proposta, analisamos os Cadernos de Ciências da Proposta Curricular do Estado de São Paulo e as teses e dissertações produzidas no Brasil nas últimas décadas, procurando investigar como estes materiais propõem atividades para o ensino-aprendizagem de conceitos de astronomia. Dialogamos com as ideias de Paulo Freire ao refletir sobre os significados da problematização, do diálogo, da atividade de Extensão Universitária e da importância da formação de sujeitos críticos para compreender o mundo que os cercam. Construímos uma proposta de ensino-aprendizagem com 12 atividades estruturadas a partir da metodologia dos Três Momentos Pedagógicos e realizamos intervenções em um curso para a formação de professores, com o caráter de extensão universitária, oferecido pela Universidade de São Paulo. O objetivo da proposta elaborada foi desenvolver o senso crítico ao relacionar a observação cotidiana com os modelos científicos atualmente aceitos, que geralmente são ensinados em sala de aula. Os dados obtidos na aplicação desta proposta foram analisados com base em três grandes categorias gerais que tinham como focos principais avaliar a percepção das limitações da observação imediata e ingênua e a contradição entre esta e o modelo científico. Os resultados parecem indicar que uma parte dos professores não percebeu a contradição aparente entre a forma da Terra observada no cotidiano e a forma descrita no modelo. Os que percebiam, forneciam argumentos com base em noções de referencial e de escalas e proporção. Embora metade dos professores de nossa amostra tenha percebido esta contradição, a maior parte deles não consegue explicar esta percepção com argumentos científicos ou astronômicos. Na problematização dos movimentos observáveis, todos os professores perceberam a contradição aparente entre o movimento do Sol e os movimentos da Terra aceitos atualmente no modelo. Ainda que apresentassem muitas dificuldades em justificar as razões disso, os professores usaram noções de observação de outros astros e planetas para justificar o modelo. Ao final do curso, percebemos que os professores apresentaram nos debates do tipo Júri Simulado uma série de argumentos trabalhados ao longo do curso, o que parece indicar que, após as atividades, eles passaram a argumentar de maneira menos ingênua sobre as relações entre a observação cotidiana e o modelo. Embora reconheçamos as limitações da proposta apresentada, esta parece se mostrar uma alternativa de grande potencial para intervenções na formação de professores que busquem trabalhar além do conhecimento presente nos materiais didáticos, promovendo um diálogo constante entre o conhecimento astronômico e os aspectos vivenciáveis no cotidiano. / The Solar System is one of the most discussed topics of Astronomy in science classes. Recognizing its importance, this study investigates a teaching-learning proposal about \"the shape and movements of the planets in the Solar System\" which focus on the relationship between daily observation and scientific models currently accepted. We analyze the sciences curriculum proposal of the State of São Paulo and theses and dissertations produced in Brazil in recent decades, describing how these materials propose activities for teaching and learning about astronomy. We have dialogued with the ideas of Paulo Freire in order to reflect on the meanings of \"problematization\", dialogue, university extension and the importance of educating critical subjects to understand the world around them. We created a teaching and learning proposal with 12 structured activities based on the methodology of Three Pedagogical Moments and interventions conducted in a course for the training of teachers, with the character of university extension, offered by the University of São Paulo. The objective of this proposal was develop a critical sense of the subjects relate to everyday observation with currently accepted scientific models, which are usually taught in the classroom. The data obtained in the implementation of this proposal were analyzed based on three main general categories that had as main focus to evaluate the perception of contradiction and limitations of immediate and naive observation and the scientific model. The results seem to indicate that some of the teachers do not realize the apparent contradiction between the Earth\'s shape observed in everyday life and as described in the model. Those who perceived provided arguments based on notions of reference and scales and proportion. Although half of the teachers in our sample have noticed this contradiction, most of them can not explain this perception with astronomical or scientific arguments. In questioning the observable movements, all teachers realized the contradiction between the apparent motion of the Sun and the Earth in the movements currently accepted model. Although presented many difficulties in justifying the reasons that many teachers have used notions of observation of other astronomical bodies and planets to justify the model. At the end of the course, we realize that the teachers presented in the discussions of the type Simulated Jury worked a series of arguments along the course, which seems to indicate that after the activities, they began to argue less naive way relations between everyday observation model. While we recognize the limitations of the proposal, this seems to show a great potential for alternative interventions in teacher seeking work beyond the present knowledge in textbooks, promoting an ongoing dialogue between the astronomical knowledge and aspects in daily life.

<div>Planetary rings are, and have been, a common feature throughout the solar system.</div><div>Rings have been observed orbiting each of the giant planets, several Trans-Neptunian Objects, and debris rings are thought to have orbited both Earth and Mars.</div><div>The bright, massive planetary rings orbiting Saturn have been observed for centuries, and the Cassini Mission has given researchers a recent and extensive closeup view of these rings.</div><div>The Saturn ring system has served as a natural laboratory for scientists to understand the dynamics of planetary ring systems, as well as their influence on satellites orbiting nearby.</div><div>Researchers have shown that planetary ring systems and nearby satellites can be tightly-coupled systems.</div><div><br></div><div>In this work, I discuss the physics which dominate the dynamical evolution of planetary ring systems, as well as the interactions with any nearby satellites.</div><div>Many of these dynamics have been incorporated into a one-dimensional mixed Eulerian-Lagrangian numerical model that I call "RING-MOONS," to simulate the long-term evolution of tightly coupled satellite-ring systems.</div><div>In developing RING-MOONS, I have discovered that there are three evolution regimes for tightly-coupled satellite-ring systems which I designate as the "Boomerang," "Torque-Dependent," and "Slingshot" regimes.</div><div>Each regime may be defined using the rotation period of the primary body and the bulk density of the ring material.</div><div><br></div><div>The slow rotation period of Mars places it in the Boomerang regime.</div><div>I hypothesize that a giant impact with Mars ejected material into orbit, forming a debris ring around the planet.</div><div>Using RING-MOONS, I demonstrate how Lindblad torques cause satellites which form at the edge of the ring to initially migrate away from the ring, but over time as the mass of the ring decreases, tidal torques always cause the satellites to migrate inwards.</div><div>Assuming the satellites rapidly tidally disrupt upon migrating to the rigid Roche limit, a new ring is formed.</div><div>I show that debris material cycles between orbiting Mars as a planetary ring, or as discrete satellites, and that Phobos may be a product of a repeated satellite-ring cycle.</div><div>Uranus, which has a faster rotation rate falls within the Torque-Dependent regime.</div><div>Hypothesizing that a massive ring once orbited Uranus, I use RING-MOONS to demonstrate how the satellite Miranda may have formed from such a ring, and migrated outwards to its current orbit, but that any other satellites would have migrated inwards overtime.</div><div><br></div><div>Lastly, I examine Trans-Neptunian Objects (TNOs) in binary systems.</div><div>Tidal torques exerted on each body can decrease the mutual semi-major axis of the system.</div><div>I outline the conditions for which a fully synchronous system may experience a complete decay of the mutual orbit due to tidal torques.</div><div>As the semi-major axis decreases, it is possible for the smaller of the two bodies to shed mass before coming into contact with the more massive to form a contact binary.</div><div>I hypothesize that Chariklo and Chiron are contact binaries that formed via the tidal collapse of a binary TNOs system, and demonstrate how mass shedding may have occurred to form the rings observed today.</div>

Au delà du système solaire et de ses planètes, nous avons maintenant un catalogue de quasiment 1000 exoplanètes qui illustrent la grande diversité des planètes et des systèmes qu'il est possible de former. Cette diversité est un défi que les modèles de formation planétaire tentent de relever. La migration de type 1 est un des mécanismes pour y parvenir. En fonction des propriétés du disque protoplanétaire, les planètes peuvent s'approcher ou s'éloigner de leur étoile. La grande variété des modèles de disques protoplanétaires permet d'obtenir une grande variété de systèmes planétaires, en accord avec la grande diversité que nous observons déjà pour l'échantillon limité qui nous est accessible. Grâce à des simulations numériques, j'ai pu montrer qu'au sein d'un même disque, il est possible de former des super-Terres ou des noyaux de planètes géantes selon l'histoire de migration d'une population d'embryons. / In addition to the Solar System and its planets, we now have a database of nearly 1000 planets that emphasize the huge diversity of planets and systems that can be formed. This diversity is a challenge for planetary formation models. Type I migration is one of the mechanisms possible to explain this diversity. Depending on disc properties, planets can migrate inward or outward with respect to their host star. The huge parameter space of protoplanetary disc models can form a huge diversity of planetary systems, in agreement with the diversity observed in the nonetheless small sample accessible to us. Thanks to numerical simulations, I showed that within the same disc, it is possible to form super-Earths or giant planet cores, depending on the migration history of an initial population of embryos.

Globulettes have recently been found in the Rosette Nebula, the Carina Nebula and other nebulæ. They are expected to be seeds of brown dwarfs and free-floating planetary-mass objects. The size distribution in the Carina Nebula was found to follow a power-law, and the same power-function resulted in 880 +- 250 globulettes in total in the Rosette Nebula. Compared to the 145 observed objects in this nebula, many globulettes are beneath the resolution limit of the Nordic Optical Telescope, which was used to explore the Rosette Nebula. A simulation that arranged all these globulettes randomly in the nebula determined that some globulettes are captured by stars. They are believed to form into one or more planets, orbiting the star thereafter. The possibility that globulettes result into the formation of planets, orbiting a star, is some 4.75·10^2 per cent. According to this simulation, about 3.35·10^3 per cent of the stars with spectral type A to M host one or more planets that once have been globulettes. / <p>Validerat; 20101217 (root)</p>