No description available.

No description available.

The field of exoplanet research has currently yielded the discovery of 552 planets. This figure includes 132 transiting planets which can be studied in greater detail and have formed the cornerstone of research to characterise the exoplanet population. In particular, such studies seek to analyse the planetary atmospheres, but research has thus far yielded more questions than answers. Exoplanetary atmospheric studies have typically focussed on one planet apiece - complicating any comparative analysis as every result employs different methods and instruments. For a comprehensive, comparative study, a robust and reliable means of reducing and analysing such observations is required, along with a body of data from a single instrument. One such instrument is the Bubble Space Telescope (BST) whose NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instrument has observed the transits of nine extrasolar planets across multiple wavelengths in the near-infrared. A robust pipeline has been developed to reduce all such observations using the fame techniques. This pipeline reduces grism images of an exoplanet host star across a transit event. These exposures are checked for bad pixels, flat fielded and background-subtracted before robust extraction of a transit light curve. This light curve is then detrended to remove systematic noise by application of a new technique developed in this study. Following detrending, the light curve is modelled using a be- spoke MCMC (Markov-Chain Monte-Carlo) algorithm to determine the planetary parameters. A continuum of wavelength-dependent transit light curves is also extracted, detrended and modelled to de- termine the variation in transit depth with wavelength; and .hereby infer the transmission spectrum of the planet's atmosphere. The finished pipeline has been applied to three sets of HST NIC- MOS observations covering the transits of WASP-2b, HD189733b and GJ436b. For each data set, a new set of planetary parameters has been derived and for WASP-2b and HD189733b an atmospheric transmission spectrum extracted. Both spectra show signs of atmospheric haze and molecular absorption, but also evidence of residual systematic noise, complicating analysis.

SuperWASP is a ground-based survey for transiting extrasolar planets. I present some of my contributions to the project's infrastructure and operations, as well as the discovery and characterisation of seven short-period, giant, transiting extrasolar planets and a 51-Jupiter-mass, transiting brown dwarf. Of particular note is the planet WASP-l7b, which is the largest known planet (Rpl = 1.99 ± 0.08 RJup ) and was the first reported to be in a retrograde orbit. WASP-17b offers one of the most extreme tests of the mechanisms suggested as responsible for the observed bloating of a subset of 'hot Jupiters'. The planet's retrograde orbit indicates that at least some hot Jupiters arrived in their current short orbits via scattering processes rather than via migration by planet-disc tidal interaction. As transiting brown dwarfs are rare, WASP-30b should prove a useful test of models. For the exoplanets WASP-22b and WASP-26b, I present spectroscopic observations of their transits. WASP-22b was found to be in a prograde orbit, but the orientation of the orbit of WASP-26b was not determined with confidence, owing to observation noise and the predicted small amplitude of the signal. I present measurements, via observations of occultations of the planets by their host stars, of the infrared thermal emission of the atmospheres of WASP-19b and WASP-17b. The atmosphere of WASP-19b appears to lack a strong atmospheric temperature inversion and inefficiently transports energy from its day-side to its night-side. For WASP-17b, the data are consistent with a low-albedo atmosphere that efficiently redistributes heat from its day-side to its night-side. For both systems, the occultation timings provide a constraint on orbital eccentricity; this proved especially useful for the WASP-17b system, as it removed the previous large uncertainty on the stellar and planetary radii.

The Solar System is formed from material processed by a wide variety of nucleosynthetic sources (Burbidge et al., 1957). Many studies have investigated the nucleosynthetic origins of the Solar System by examining the isotopic anomalies within meteorites and their constituent components. However, debate continues as to the astrophysical source these anomalies represent and the early Solar System processes that results in their inhomogeneous distribution. Nickel isotopes offer an opportunity to examine further the sources and mixing of early Solar System materials. Nickel is an abundant element in most meteorite groups (normally wt. %) with five stable isotopes that are dominantly produced in different astrophysical environments. A new high resolution mass spectrometric technique has been developed and has been examined for potential analytical artefacts; none are found to have a significant effect. Currently, this technique produces the highest precision «10 ppm) data for all Ni isotope including the least abundant, 64Ni, which has previously only been reported in two studies (Cook et al., 2006; Dauphas et al., 2008). New Ni isotope data are presented for a range of bulk chondritic and iron meteorites which, when normalised to 58Ni/61 Ni and presented as part per ten thousand difference (%00) from NIST SRM 986, show ranges of 0.18, 0.35 and 0.9 %00 for c6oNiH, c62NiH and c64NiHrespectively. A strong positive correlation is observed between c62NiH and c64NiH with gradient 2.98 ±0.21, which is within error of the slope produced between the terrestrial composition and the average of early measurements of calcium, aluminium-rich inclusionss (CAls) (Birck and Lugmair, 1988). Interestingly, this gradient is also within error of the slope expected for isotopic anomalies on 58Ni. 'Absolute' Ni isotope ratios determined on two meteorites (Orgueil Cl and Butsura OC) to <0.3 %00 (2 s.e.) confirm that anomalies reside on 58Ni. This finding of neutron-poor anomalies has significance for the interpretation of anomalies in other elements. The nucleosynthetic origins of these meteorite anomalies have been quantitatively investigated using a holistic approach which considers potential anomalies from all isotopes, including those used for normalisation. I argue that such an approach should be taken for all elements. It has been found that no bulk astrophysical environment can provide a robust case as the source of Ni isotope anomalies in meteorites. However, a more promising result is found in the model composition of the Si/S shell of type II supernovae (SN II) (Rauscher et al., 2002). The Si/S zone of all masses of SN II investigated (12-40 Md can meet the Ni isotope constraints set by the measurements of early Solar System materials. This finding removes the need for input from the rare type la supernova, which is considered unlikely to be associated with star forming regions. Although this places narrow constraints on the nucleosynthetic source for material containing anomalous Ni isotopes, this Si/S zone cannot account for all the Ni isotope anomalies (e.g. f:6oNiSf is not perfectly correlated with f:58NiSf) nor the anomalies of all other elements. This suggests a major control on isotopic anomalies observed in meteorites may be which zones of supernovae are sampled by robust pre-solar carriers and how these carrier phases are differentially mixed in by nebula processing. More insight in to these processes and sources could gained by identifying the carrier phases of isotopic anomalies.

No description available.

No description available.

Since the first discovery of a transiting planet in 2000, transmission spectroscopy has proved essential for characterising the rapidly increasing number of known extrasolar planets. When a planet is in a favourable alignment, it periodically passes (transits) in front of its host star, during which time it blocks a fraction of the stellar light. During a transit, the starlight passes through the planetary atmosphere, causing the signatures of atoms or molecules present in that atmosphere to imprint themselves on the stellar spectrum, allowing direct observation of a planet's atmospheric composition. At the start of this thesis, only two planets (HD 189733b and HD 209458b) had been studied in any detail, mainly from space. The two planets showed surprisingly different qualities for two objects with only a small temperature difference between them, and motivated both wider and more detailed studies of the exoplanet population. Since the start of my PhD, the amount of exoplanet knowledge has grown rapidly, with observations from the ground becoming important, and with studies branching out towards new planets. There are several contributions made by this thesis to the field. Chapter 3 details the detection of the resolved sodium D doublet in the atmosphere of HD 189733b, a planet with a featureless broad-band transmission spectrum dominated by Rayleigh scattering. The results confirmed the presence of sodium absorption as well as resolving the feature for the first time, and placing constraints on relative abundances. Furthermore, in Chapter 4, I outline a method based on earlier work which allows observers to retrieve atmospheric temperature information from resolved spectral features. This method is applied to the observations of HD 189733b, showing that the planet has a hot thermosphere similar to HD 209458b. The models are then also used in later chapters. I then present the first results from a ground-based optical long-slit spectroscopic survey in Chapter 5, and the first results from a space-based optical-near-IR spectroscopic survey in Chapter 6. From the ground, I detect absorption from sodium in the atmosphere of XO-2b, making this the first planet with sodium and potassium detected in its atmosphere. I also find that the Na I D feature lacks broad line wings, suggesting haze or cloud cover. From space, I observed the transmission spectrum of WASP-19b, finding solar abundance water features and a likely lack of predicted TiO features. WASP-19b is the first planet to have confirmed water features at solar-abundance level. In Chapter 7 I conclude and discuss future work, including a project aimed at understanding why WASP-19b lacks TiO features, and projects which move beyond the hot Jupiter class.

L'effet de microlentille gravitationnelle est devenu un outil unique pour détecter des exoplanètes. Il se produit lorsqu'une étoile de premier plan (la microlentille) et une étoile d'arrière plan (la source) sont alignées avec la Terre. La lumière provenant de l'étoile la plus lointaine, souvent dans le bulbe galactique, est alors déviée par la microlentille située dans le disque. Au cours de ce phénomène, des images multiples de la source sont créées par la microlentille, plus grandes que la source, qui apparaît alors amplifiée. Si l'une de ces images multiples se forme au voisinage d'une planète, un pic d'amplification de la source survient, révélant sa présence. Après un tour d'horizon de l'état des connaissances dans le domaine des exoplanètes, nous décrivons les spécificités de la méthode des microlentilles dans ce domaine. Ensuite, nous présentons en détail la modélisation des microlentilles, de ses racines théoriques à la modélisation pratique des courbes de lumières expérimentales. Dans une troisième partie, nous présentons la détection de la première naine brune en orbite autour d'une étoile de type solaire par la méthode des microlentilles, et nous montrons en quoi cette technique ouvre des perspectives nouvelles et originales pour mieux connaître les mécanismes de formation de ces objets dont l'origine reste à identifier. Nous étudions enfin le potentiel de l'observation de microlentilles par interférométrie, en introduisant un nouveau formalisme adapté à l'étude conjointe des événements en photométrie et en interférométrie. Le manuscrit se termine par l'évaluation du nombre moyen d'événements de microlentille observables par interférométrie chaque année. / Gravitational microlensing effect has become a unique tool to detect and characterise exoplanets. A microlensing effect occurs when a foreground star (the microlens) and a background star (the source) are aligned with the Earth on the same line of sight. The light from the furthest star, usually in the Galactic bulge, is deflected by the microlens located on the disk. During this phenomenon, multiple images of the source are created by the lens, bigger than the source that consequently seems amplified. When one of these images are located in the vicinity of an exoplanet, a short amplification jump occurs revealing its presence. After a quick overview of the exoplanets field of research, I highlight the specificities of microlensing comparing to the other planets detection techniques. Then, I describe in details the modelling of microlensing effects, from a theoretical to a numerical point of view. In a third part, I describe the detection of the first brown dwarf orbiting a solar-type star using microlensing, strengthening the recent idea that microlensing will lead to a better understanding of the mechanisms involved in the brown dwarfs formation, still not fully understood. Finally, I investigate the potential of interferometric observations of microlensing events that will give, in the future, new original constrains on the microlens physical properties. First we introduce a new formalism that closely combines interferometric and microlensing observable quantities. Secondly, we determine an average number of events that are at reach of long baseline interferometers every year.