The transit method of detecting extrasolar planets relies on the small periodic changes in the brightness of the planet's host star as the planet orbits between the observer and the star. Transiting planets are extremely useful discoveries due to the significant gain in information that can be obtained on the planet and its host star than extrasolar planets discovered with other methods. The field of transiting planets has matured rapidly in the last 5 years, particularly in the area of wide-field surveys. This thesis describes the results of two such surveys. The Vulcan South Antarctic Planet Finder was designed to exploit the conditions at the South Pole, which are ideal for a transit survey. Several hardware failures resulted in the acquisition of only a small amount of corrupted data on a single field. The University of New South Wales Extrasolar Planet Search is an ongoing transit survey using the 0.5-m Automated Patrol Telescope at Siding Spring Observatory, Australia. 25 fields were observed for 1-4 months each between 2004 October and 2007 May. Light curves were constructed for ~87,000 stars down to I= 14th magnitude, and from these 23 planet candidates were identified. Ten candidates were eliminated using higher spatial resolution archived images and online catalogue data. Eight were followed up with higher spatial resolution imaging and/or medium resolution spectroscopy and were determined to be eclipsing binaries. Five candidates remain that require additional observation to determine their nature. No planets have been confirmed in this data set thus far. The large sets of high precision light curves generated by transit surveys hold significant potential for additional data-mining. To demonstrate this, a variable star catalogue was compiled from the full data set. A total of 850 variable stars were identified, with 659 new discoveries. In the course of compiling this catalogue, the first example of a high-amplitude δ Scuti star in an eclipsing binary was identified. This represented the first opportunity for a dynamical mass measurement of a highamplitude δ Scuti star, and the system was studied comprehensively.

The transit method of detecting extrasolar planets relies on the small periodic changes in the brightness of the planet's host star as the planet orbits between the observer and the star. Transiting planets are extremely useful discoveries due to the significant gain in information that can be obtained on the planet and its host star than extrasolar planets discovered with other methods. The field of transiting planets has matured rapidly in the last 5 years, particularly in the area of wide-field surveys. This thesis describes the results of two such surveys. The Vulcan South Antarctic Planet Finder was designed to exploit the conditions at the South Pole, which are ideal for a transit survey. Several hardware failures resulted in the acquisition of only a small amount of corrupted data on a single field. The University of New South Wales Extrasolar Planet Search is an ongoing transit survey using the 0.5-m Automated Patrol Telescope at Siding Spring Observatory, Australia. 25 fields were observed for 1-4 months each between 2004 October and 2007 May. Light curves were constructed for ~87,000 stars down to I= 14th magnitude, and from these 23 planet candidates were identified. Ten candidates were eliminated using higher spatial resolution archived images and online catalogue data. Eight were followed up with higher spatial resolution imaging and/or medium resolution spectroscopy and were determined to be eclipsing binaries. Five candidates remain that require additional observation to determine their nature. No planets have been confirmed in this data set thus far. The large sets of high precision light curves generated by transit surveys hold significant potential for additional data-mining. To demonstrate this, a variable star catalogue was compiled from the full data set. A total of 850 variable stars were identified, with 659 new discoveries. In the course of compiling this catalogue, the first example of a high-amplitude δ Scuti star in an eclipsing binary was identified. This represented the first opportunity for a dynamical mass measurement of a highamplitude δ Scuti star, and the system was studied comprehensively.

This study presents the development of an observing program to pursue the idea of looking for transiting exoplanets in eclipsing binary stars. The various kinds of orbits a planet might have in a binary system are explored. From this it is shown how to anticipate the possible orbits a planet might have in a given star system. The potential detectability of a planet in a binary system is also analyzed. Together these guidelines enable observers to rank targets by the likelihood that a detectable planet might exist in the system. The results of observations by a team at Ball State University of five binary star systems chosen with these guidelines are presented. / Department of Physics and Astronomy

ISIS is a program that specializes in detecting variable stars within clusters, both open and globular. ISIS has historically been used in surveys searching for variable stars. However, recent work has identified new uses for ISIS, such as the detection of exoplanet transits in clusters of stars. This thesis will evaluate ISIS, both how the program functions and for which objects it is most efficient and appropriate. I examined five clusters: three open, and two globular, for one night surveys. With this survey, I identified twenty-five variable stars. Twenty-two variables were previously known, and three variable stars were previously undiscovered. In total, from my short one night surveys, I confirmed twenty-five previously known variable stars and four unknown variable stars. Furthermore, ISIS has detected several δ Scuti stars whose amplitude of variation is on par with an exoplanet transit. These data suggest that ISIS can be used for the detection of exoplanet transits. / Department of Physics and Astronomy

The transit method is considered to be one of the most promising for discovering extrasolar planets. However, the method requires photometric precision of better than ∼ 1%. If we are able to achieve this kind of accuracy, then we are set to discover extrasolar planets. The uniqueness of my experiment will lead to the discovery of transiting planets around the brightest and most important stars quicker than the competitors in the field. The importance of the transit method stems from being able to supply many more planetary parameters than other methods, which plays a crucial role in testing planet formation theories. This thesis is divided into eight chapters. The first chapter provides a general background about transits and their theory. We discuss other methods of extrasolar planet detection, recent developments, future space missions, and what we have learned so far about properties of hot Jupiters. The second chapter details the theory of signals and noise on CCDs followed by the design of the PASS0 experiment. The third chapter reports on the difference imaging data pipeline that we developed and applied to a set of PASS0 data to search for transiting planets. The fourth chapter shows how we apply the PASS0 pipeline to SuperWASP data and improve on the accuracy obtained with their aperture photometry pipeline. The fifth chapter reports on the search for variable stars from the PASS0 and SuperWASP data sets that we consider in this thesis. In the sixth chapter we perform a transit search on the PASS0 and SuperWASP data sets and report the results. In the seventh chapter we use the PASS0 pipeline to process a full season of observing data from 2007 for two recent planet discoveries, WASP-7b and WASP-8b, that have not yet been announced. We analyse their lightcurves and predict their radii. Finally we conclude in the eighth chapter.

This first part of this thesis concerns the discovery and parameter determination of three hot Jupiter planets, first detected with by the SuperWASP collaboration, and their planetary nature is confirmed with the modelling of radial velocity measurements and further ground-based transit lightcurves. WASP-92b, WASP-93b and WASP-118b are all hot Jupiters with short orbital periods – 2.17, 2.73 and 4.05 days respectively. The analysis in this thesis finds WASP-92b to have R[sub]p = 1.461 ± 0.077 R[sub]J and M[sub]p = 0.805 ± 0.068 M[sub]J; WASP-93b to have R[sub]p = 1.597 ± 0.077 R[sub]J and M[sub]p = 1.47 ± 0.029 M[sub]J, and WASP-118b to have R[sub]p = 1.440 ± 0.036 R[sub]J and M[sub]p = 0.514 ± 0.020 M[sub]J. The second part of this thesis presents three novel approaches to modelling the effect of stellar limb darkening when fitting exoplanet transit lightcurves. The first method trains a Gaussian Process to interpolate between pre-calculated limb darkening coefficients for the non-linear limb darkening law. The method uses existing knowledge of the stellar atmosphere parameters as the constraints of the determined limb darkening coefficients for the host star of the transiting exoplanet system. The second method deploys an artificial neural network to model limb darkening without the requirement of a parametric approximation of the form of the limb profile. The neural network is trained for a specific bandpass directly from the outputs of stellar atmosphere models, allowing predictions to be made for the stellar intensity at a given position on the stellar surface for values of the T[sub]eff , log g and [Fe/H]. The efficacy of the method is demonstrated by accurately fitting a transit lightcurve for the transit of Venus, and for a single transit lightcurve of TRES-2b. The final limb darkening modelling method proposes an adjustment to the neural network model to account for the fact that the stellar radius is not constant across wavelengths. The method also allows the full variation in light at the edge of the star to be modelled by not assuming a sharp boundary at the limb.

We search for planets and brown dwarves around white dwarves (WDs). Finding extra-solar planets is the first step toward establishing the existence and abundance of life in the Universe. The low mass and luminosity of WDs make them ideal stars to search for low mass companion objects. Theoretical predictions generally agree that a star will consume and destroy close-in, low mass planets as it ascends the red giant and asymptotic giant branch evolutionary tracks, but larger mass objects and those further out will survive. The matter ejected from the star as it evolves into a white dwarf may also be accreted onto daughter planets, or may coalesce into a disk from which planets can form. We employ two techniques to search for planets and brown dwarves (BDs) around WDs. A subset of pulsating white dwarf stars have a pulsational stability that rivals pulsars and atomic clocks. When a planet is in orbit around a such a star the orbital motion of the star around the centre of mass is detectable as a change in arrival times of the otherwise stable pulsations. We search for, and find, a sample of suitable pulsators, monitor them for between three and four years, and place limits on companions by constraining the variation consistent with a 2.4M[subscript J] planet in a 4.6 year orbit. We also observe a large sample of WDs to search for a mid-infrared excess caused by the presence of sub-stellar companions. We present evidence for a potential binary system consisting of a WD and a BD on the basis of an observed excess flux at near and mind-infrared wavelengths. We also place limits on the presence of planetary mass companions around those stars and compare our results to predictions of planetary survival theories. Our findings do not support suggestions of planet formation or accretion of extra mass during stellar death.

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.

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 detection of low-mass extra-solar planets through radial-velocity searches is currently limited by the intrinsic magnetic activity of the host stars. The correlated noise that arises from their natural radial-velocity variability can easily mimic or conceal the orbital signals of super-Earth and Earth-mass extra-solar planets. I developed an intuitive and robust data analysis framework in which the activity-induced variations are modelled with a Gaussian process that has the frequency structure of the photometric variations of the star, thus allowing me to determine precise and reliable planetary masses. I applied this technique to three recently discovered planetary systems: CoRoT-7, Kepler-78 and Kepler-10. I determined the masses of the transiting super-Earth CoRoT-7b and the small Neptune CoRoT-7c to be 4.73 ± 0.95 M⊕ and 13.56 ± 1.08 M⊕, respectively. The density of CoRoT-7b is 6.61 ± 1.72 g.cm⁻³, which is compatible with a rocky composition. I carried out Bayesian model selection to assess the nature of a previously identified signal at 9 days, and found that it is best interpreted as stellar activity. Despite the high levels of activity of its host star, I determined the mass of the Earth-sized planet Kepler-78b to be 1.76 ± 0.18 M⊕. With a density of 6.2(+1.8:-1.4) g.cm⁻³, it is also a rocky planet. I found the masses of Kepler-10b and Kepler-10c to be 3.31 ± 0.32 M⊕ and 16.25 ± 3.66 M⊕, respectively. Their densities, of 6.4(+1.1:-0.7) g.cm⁻³ and 8.1 ± 1.8 g.cm⁻³, imply that they are both of rocky composition – even the 2 Earth-radius planet Kepler-10c! In parallel, I deepened our understanding of the physical origin of stellar radial-velocity variability through the study of the Sun, which is the only star whose surface can be imaged at high resolution. I found that the full-disc magnetic flux is an excellent proxy for activity-induced radial-velocity variations; this result may become key to breaking the activity barrier in coming years. I also found that in the case of CoRoT-7, the suppression of convective blueshift leads to radial-velocity variations with an rms of 1.82 m.s⁻¹, while the modulation induced by the presence of dark spots on the rotating stellar disc has an rms of 0.46 m.s⁻¹. For the Sun, I found these contributions to be 2.22 m.s⁻¹ and 0.14 m.s⁻¹, respectively. These results suggest that for slowly rotating stars, the suppression of convective blueshift is the dominant contributor to the activity-modulated radial-velocity signal, rather than the rotational Doppler shift of the flux blocked by starspots.