Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 115-124).

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 166-174).

Since the first discovery of an extrasolar planet around a solar-type star, observers have detected over 500 planets outside the solar system. Many of these planets have Jovian masses and orbit their host stars in orbits of only a few days, the so-called 'Hot Jupiters'. At such close proximity to their parent stars, strong tidal interactions between the two bodies are expected to cause significant secular spin-orbit evolution. This thesis tackles two problems regarding the tidal evolution of short-period extrasolar planets. In the first part, we adopt a simple model of the orbit-averaged effects of tidal friction, to study the tidal evolution of planets on inclined orbits. We also analyse the effects of stellar magnetic braking. We then discuss the implications of our results for the importance of Rossiter-Mclaughlin effect observations. In the second part, we study the mechanisms of tidal dissipation in solar-type stars. In particular, internal gravity waves are launched at the interface of the convection and radiation zones of such a star, by the tidal forcing of a short-period planet. The fate of these waves as they approach the centre of the star is studied, primarily using numerical simulations, in both two and three dimensions. We find that the waves undergo instability and break above a critical amplitude. A model for the tidal dissipation that results from this process is presented, and its validity is verified by numerical integrations of the linear tidal response, in an extensive set of stellar models. The dissipation is efficient, and varies by less than an order of magnitude between all solar-type stars, throughout their main-sequence lifetimes, for a given planetary orbit. The implications of this mechanism for the survival of short-period extrasolar planets is discussed, and we propose a possible explanation for the survival of all of the extrasolar planets currently observed in short-period orbits around F, G and K stars. We then perform a stability analysis of a standing internal gravity wave near the centre of a solar-type star, to understand the early stages of the wave breaking process in more detail, and to determine whether the waves are subject to weaker parametric instabilities, below the critical amplitude required for wave breaking. We discuss the relevance of our results to our explanation for the survival of short-period planets presented in the second part of this thesis. Finally, we propose an alternative mechanism of tidal dissipation, involving the gradual radiative damping of the waves. Based on a simple estimate, it appears that this occurs even for low mass planets. However, it is in conflict with current observations since it would threaten the survival of all planets in orbits shorter than 2 days. We discuss some hydrodynamic instabilities and magnetic stresses which may prevent this process.

No description available.

Over two hundred extrasolar planets have been discovered to date with various methods. This thesis reports on searching for extrasolar planets and characterising them by simulating their atmospheres. We used open clusters as targets for deep transit searches, with specific emphasis on the University of St. Andrews Planet Search at the Isaac Newton Telescope. We reduced CCD photometry and described the algorithm we used to search for transits. We estimated the number of transits we expect from our data. We then reduced photometry for the open cluster NGC 6940. From that data we found 18 low-amplitude, short-duration events, though none are transiting planets. They are all eclipsing binary stars. However, our null result constrains the number of planets around M dwarfs, the most numerous stars in our sample. In order to characterise reflected light from extrasolar planets, we built a three-dimensional Monte Carlo based radiation transfer model of extrasolar planetary atmospheres. We detailed the input parameters of the model, and show results of various models, focusing especially on the fractal nature of the clouds of our models, because these are the first three dimensional radiation transfer models of extrasolar planet atmospheres. We found very low geometric albedos in our simulations. Using data specific to the transiting planet HD 209458b, we built a model atmosphere with Rayleigh-scattering hydrogen gas and clouds of enstatite and iron. We show in several models the rarity of a bright HD 209458b, and conclude with some explanations on why extrasolar planets are likely dark and not detected with reflected light.

La recherche des exoplanètes traverse aujourd'hui une période décisive. D'un côté, notre connaissance des planètes géantes gazeuses s'est considérablement développée, et l'objectif de la recherche est maintenant de caractériser leurs propriétés physiques et de mieux comprendre leurs mécanismes de formation et d'évolution. D'un autre côté, la précision et la stabilité des instruments ont atteint un niveau qui rend techniquement possible la détection de planètes telluriques situées dans la zone habitable de leur étoile. Cependant, les perturbations du signal dues à l'étoile elle-même constituent un obstacle important à cette avancée. Mon travail de thèse se situe à la rencontre de ces problématiques. Il a consisté d'une part en l'analyse de deux relevés de vitesses radiales visant des étoiles relativement exotiques pour la recherche d'exoplanètes: les étoiles naines de type AF massives. Ce travail a donné lieu à la première caractérisation de la population de planètes géantes autour de ces étoiles et a montré que les mécanismes de migration planétaire étaient au moins partiellement inhibés autour de ces étoiles par rapport aux étoiles de type FGKM. Dans un second temps, j'ai conduit les observations et l'analyse des premiers résultats de deux grands relevés de vitesses radiales débutés pendant ma thèse et visant à détecter des planètes géantes en orbite autour d'étoiles jeunes et proches. Ces étoiles jeunes sont les seules sources pour lesquelles une exploration complète des planètes géantes à toutes les séparations devient possible, par combinaison des techniques de vitesses radiales et de l'imagerie. Cette combinaison permettra de tester de manière unique les modèles de formation et d'évolution planétaire. Les résultats provisoires de ces relevés indiquent une absence de planètes géantes à très courte séparation (Jupiters chauds) autour de nos cibles. Un autre résultat intéressant est la découverte d'une binaire spectroscopique eccentrique au centre d'un système planétaire imagé à grande séparation. Pour compléter cette approche observationnelle et mieux évaluer la détectabilité des exoplanètes semblables à la Terre, j'ai étalonné et caractérisé un modèle entièrement paramétré de l'activité d'une étoile semblable au Soleil et de son impact sur les vitesses radiales. Je l'ai dans un premier temps étalonné en comparant ses résultats à ceux obtenus à partir d'observations des zones actives du Soleil, puis je l'ai utilisé pour caractériser l'impact de l'inclinaison de l'étoile sur le signal induit par l'activité. Ce modèle paramétré ouvre de très nombreuses possibilités, étant en effet potentiellement adaptable à des types d'étoiles et d'activité différents. Il permettrait ainsi de caractériser les perturbations en vitesses radiales attendues pour chaque cas testé, et donc à la fois de déterminer quelles étoiles et quels types d'activité sont les plus favorables pour la détection de planètes de masse terrestre dans la zone habitable. En explorant ces trois problématiques en apparence très diverses mais complémentaires, j'y ai retrouvé un motif commun, celui de l'importance des étoiles elles-mêmes et de la physique stellaire pour la recherche d'exoplanètes. / The search for exoplanets has reached a decisive moment. On the one hand, our knowledge of giant gaseous planets has significantly developed, and the aim of the research is now to characterize their physical properties and to better understand the formation and evolution processes. On the other hand, the instrumental precision and stability have reached a level that makes it technically possible to detect telluric planets in the habitable zone of their host star. However, the signal alterations induced by the star itself definitely challenge this breakthrough. My PhD stands at the crossroads of these problems. It consisted first in the analysis of two radial velocity surveys dedicated to stars somewhat exotic to exoplanet searches: the massive AF dwarf stars. This work has led to the first characterization of the giant planet population found around these stars and has showed that the planetary migration mechanisms were at least partially inhibited around these stars compared to FGKM stars. I then made the observations and the first analysis of two radial velocity surveys dedicated to the search for giant planets around young, nearby stars. Young stars are the only sources for which a full exploration of the giant planets at all separations can be reached, through the combination of radial velocities techniques and direct imaging. Such a combination will allow to test uniquely the planetary formation and evolution processes. The first results of these surveys show an absence of giant planets at very short separations (Hot Jupiters) around our targets. Another interesting result is the detection of an eccentric spectroscopic binary at the center of a planetary system imaged at a wide separation. To complete this observational approach and better estimate the detectability of Earth-like planets, I calibrated and characterized a fully parameterized model of the activity pattern of a Sun-like star and its impact on the radial velocities. I first calibrated it by comparing it to the results obtained with observations of the solar active structures, and then characterized the impact of stellar inclination on the activity-induced signal. Such a fully parameterized model is potentially adaptable to different types of stars and of activity and would thus allow to characterize the expected radial velocity jitter for each tested case, and then allow both to determine which types of stars and of activity patterns are the most favorable for detecting Earth-like planets in the habitable zone. While investigating these three seemingly different but complementary topics, I found that they shared a basic feature, namely the importance of the stars themselves and of stellar physics in exoplanet searches.

The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to similar to 100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs.

The search for planets orbiting stars other than the Sun has led to the discovery of over one thousand new worlds. The majority of these planets have been very large, Jupiter sized planets located very close to their host star. Transit surveys such as Kepler and SuperWASP monitor thousands of stars looking for periodic dips in light caused by a planet passing between our view point on Earth and their host star, blocking a fraction of the emitted star light. One of the primary limitations in detecting a small, Earth sized planet comes from stellar activity induced signals within the data collected by exoplanet missions. These signals can, however, be used to our advantage. In this thesis, asymmetries in transit light curves are exploited to reveal properties of both the planet and the host stars themselves. An asymmetry in the near-ultraviolet transit light curve of WASP-12b, one of the largest and hottest planets found to date is thought to be caused by the stellar wind interacting with the magnetic field surrounding the planet. In this thesis, a model for such an interaction is developed and is shown to be consistent with the observations, providing the first potential evidence for the presence of a magnetic field around an exoplanet. The model is then extended to predict the shape of near-ultraviolet light curves around HD 189733b, another hot Jupiter that orbits a very bright star. By looking at the variability in these transit light curves over time, the evolution and structure of the stellar wind is investigated. By tracking the position of bumps in the transit light curve, it is shown here that the data collected by missions such as Kepler has the potential to reveal stellar butterfly patterns. Such patterns are intrinsically linked with the stellar dynamo which governs the properties of the stellar magnetic field. Finally, the support of large-scale magnetic loops on young stars is investigated. These loops trap large amounts of hot, dense material and so a rapid destabilisation could lead to a flaring event, which could have devastating consequences for a nearby exoplanet.

The discovery and characterization of exoplanetary systems is a new exciting field. At just over two decades old, it has already fundamentally reshaped our knowledge of planet and solar system formation. We now know that there is a vast diversity of planetary systems, in highly varied, even bizarre, configurations. Known planetary bodies span all masses from objects less massive and smaller than Earth to objects as large as the smallest stars or brown dwarfs. They exhibit periods of but a few hours to periods spanning millennia, from nearly perfectly circular orbits to highly elliptical, from fluffy gas giants to dense rocky worlds, from purely metallic worlds to water worlds. Exoplanets come in all sizes, compositions and varieties. These new discoveries have fundamentally changed the way we approach planetary science. With such a great diversity in exoplanets, we look extend our knowledge to including understanding their individual composition. We wish to understand the climate of these exoplanets and to resolve the differences between, for example, Earth-like and Venus-like planets. To facilitate these discoveries several methods of exoplanery detection and characterization have been developed. Among them are indirect methods that infer the existence of exoplanets from their influence on their star, and direct methods that detect the light from the exoplanets themselves. Direct detection of exoplanets allows not only for a determination of the existence of the object, but also for the determination of its composition and climate through the measurement of its atmosphere's chemical composition. Using purely high-contrast direct imaging methods, coarse spectra can now be measured for exoplanets with a relative brightness 10⁻⁴-10⁻⁵ below that of the host star. Below this contrast level the companion is at the same level of brightness as the noise caused by optical defects and wave front errors in the observed light, called speckles. In this thesis, I demonstrate the usage and optimization of a new novel technique, S4_Spectrum, to model and remove speckle noise from directly imaged systems. S4_Spectrum is capable of reducing 99% of the speckle noise. This allows for the detection and spectral characterization of exoplanets as faint as 10⁻⁶-10⁻⁷ times the brightness of their host stars. This represents two orders of magnitude gain in sensitivity. I present the design of one of these high-contrast systems, Project 1640, as well as the data collection method, including the data pipeline and analysis techniques. Also, I describe the S4_Spectrum technique in detail, as implemented in Project 1640, and present its operation and optimization. Additionally, I present the application of this new tool to obtain several spectral characterizations of objects found in the Project 1640 survey.

Since 1995, more than 150 extrasolar planets were detected, of which a considerable fraction orbit their host star at very close distances. Gas giants with orbital distances below 0.1 AU are called “Hot Jupiters”. Current detection techniques are not sensitive enough for the detection of Earth-like planets, but such planets are expected at similar orbital positions. For all these so-called close-in extrasolar planets, the interaction between the stellar wind and the planetary magnetosphere is expected to be very different from the situation known from the solar system. Important differences arising from the close substellar distances include a low stellar wind velocity, a high stellar wind density and strong tidal interaction between the planet and the star. This interaction is shown to lead, for example, to a synchronisation of the planetary rotation with its orbit (“tidal locking”). Taking these points into account, planetary magnetic moments are estimated and sizes of planetary magnetospheres are derived. Two different effects resulting from the magnetospheric interaction are studied in detail. (a) Characteristics of radio emission from the magnetospheres of “Hot Jupiters” are discussed. It is shown that the frequency range and the sensitivity of current radio detectors are not sufficient to detect exoplanetary radio emission. With planned improvements of the existing instrumentation and with the construction of new radio arrays, the detection of exoplanetary radio emission will be possible in the near future. (b) The flux of galactic cosmic rays to the atmospheres of terrestrial exoplanets in close orbits around M stars is studied. Different types of planets are shown to be weakly protected against cosmic rays, which is likely to have implications for planetary habitability. This should be taken into account when selecting targets for the search for biosignatures in the spectra of terrestrial exoplanets.