To date, more than 300 planets orbiting stars other than our sun have been discovered using a range of observing techniques, with new discoveries occuring monthly. The work in this thesis focused on the detection of exoplanets using the transit method. Planets orbiting close to their host stars have a roughly 10 per cent chance of eclipsing (transiting) the star, with Jupiter?sized planets causing a one per cent dip in the flux of the star over a few hours. A wealth of orbital and physical information on the system can be extracted from these systems, including the planet density which is essential in constraining models of planetary formation. To detect these types of planets requires monitoring tens of thousands of stars over a period of months. To accomplish this, we conduct a wide-field survey using the 0.5-meter Automated Patrol Telescope (APT) at Siding Spring Observatory (SSO) in NSW, Australia. Once candidates were selected from the data?set, selection criteria were applied to separate the likely planet candidates from the false?positives. For this thesis, the methods and instrumentation used in attaining data and selecting planet candidates are discussed, as well as the results and analysis of the planet candidates selected from star fields observed from 2004?2007. Of the 65 planet candidates initially selected from the 25 target fields observed, only two were consistent with a planet transit. These candidates were later determined to be eclipsing binary stars based on follow up observations using the 40-inch telescope, 2.3-m telescope, and the 3.9-m Anglo-Australian Telescope, all located at SSO. Additionally, two planet candidates from the SuperWASP-North consortium were observed on the 40-inch telescope. Both proved to be eclipsing binary stars. While no planets were found, our search methods and results are consistent with successful transit surveys targeting similar fields with stars in a similar magnitude range and using similar methods.

In der vorliegenden Arbeit werden Methoden der Erdsystemanalyse auf die Untersuchung der Habitabilität terrestrischer Exoplaneten angewandt. Mit Hilfe eines parametrisierten Konvektionsmodells für die Erde wird die thermische Evolution von terrestrischen Planeten berechnet. Bei zunehmender Leuchtkraft des Zentralsterns wird über den globalen Karbonat-Silikat-Kreislauf das planetare Klima stabilisiert. Für eine photosynthetisch-aktive Biosphäre, die in einem bestimmten Temperaturbereich bei hinreichender CO2-Konzentration existieren kann, wird eine Überlebenspanne abgeschätzt. Der Abstandsbereich um einen Stern, in dem eine solche Biosphäre produktiv ist, wird als photosynthetisch-aktive habitable Zone (pHZ) definiert und berechnet. Der Zeitpunkt, zu dem die pHZ in einem extrasolaren Planetensystem endgültig verschwindet, ist die maximale Lebenspanne der Biosphäre. Für Supererden, massereiche terrestrische Planeten, ist sie umso länger, je massereicher der Planet ist und umso kürzer, je mehr er mit Kontinenten bedeckt ist. Für Supererden, die keine ausgeprägten Wasser- oder Landwelten sind, skaliert die maximale Lebenspanne mit der Planetenmasse mit einem Exponenten von 0,14. Um K- und M-Sterne ist die Überlebensspanne einer Biosphäre auf einem Planeten immer durch die maximale Lebensspanne bestimmt und nicht durch das Ende der Hauptreihenentwicklung des Zentralsterns limitiert. Das pHZ-Konzept wird auf das extrasolare Planetensystem Gliese 581 angewandt. Danach könnte die 8-Erdmassen-Supererde Gliese 581d habitabel sein. Basierend auf dem vorgestellten pHZ-Konzept wird erstmals die von Ward und Brownlee 1999 aufgestellte Rare-Earth-Hypothese für die Milchstraße quantifiziert. Diese Hypothese besagt, dass komplexes Leben im Universum vermutlich sehr selten ist, wohingegen primitives Leben weit verbreitet sein könnte. Unterschiedliche Temperatur- und CO2-Toleranzen sowie ein unterschiedlicher Einfluss auf die Verwitterung für komplexe und primitive Lebensformen führt zu unterschiedlichen Grenzen der pHZ und zu einer unterschiedlichen Abschätzung für die Anzahl der Planeten, die mit den entsprechenden Lebensformen besiedelt sein könnten. Dabei ergibt sich, dass komplex besiedelte Planeten heute etwa 100-mal seltener sein müssten als primitiv besiedelte. / In this thesis methods of Earth system analysis are applied to the investigation of the habitability of terrestrial exoplanets. With the help of parameterized convection models for the Earth the thermal evolution of terrestrial planets is calculated. Under increasing central star luminosity the global carbonate-silicate cycle stabilizes the planetary climate. The life span of a photosynthetic-active biosphere existing in a certain temperature interval under adequate CO2 concentration is estimated. The range of orbital distances within which such a biosphere is productive is defined as the photosynthetic-active habitable zone (pHZ) and is calculated. The maximum life span of the biosphere is the point in time when the pHZ of an extrasolar planetary system finally disappears. For super-Earths, i.e. massive terrestrial planets, it is as longer as more massive the planet is and as shorter as more the planet is covered with continents. For super-Earths, which are not pronounced land or water worlds, the maximum life span scales with the planetary mass with an exponent of 0.14. The life span of the biosphere on a planet around K- or M-stars is always determined by the maximum life span and not limited by the end of the main-sequence evolution of the central star. The pHZ approach is applied to the extrasolar planetary system Gliese 581. Accordingly the super-Earth of 8 Earth masses Gliese 581d could be habitable. Based on the presented pHZ concept the Rare Earth Hypothesis established by Ward and Brownlee 1999 is quantified for the Milky Way. This hypothesis claims that complex life may be very rare in the Universe while primitive life is likely common and widespread. Different temperature and CO2 tolerances as well as a different influence on weathering of complex and primitive life forms result different boundaries of the pHZ and a different estimate of the number of planets potentially harboring these different life forms. It arises that planets with complex life might be 100 times rarer than primitive life bearing planets.

Nightly surveys of the skies detect thousands of new gravitational microlensing events every year. With the increasing number of telescopes, and advancements of the tech- nologies used, the detection rate is growing. Of these events, those that display the characteristics of a binary lens are of particular interest. They require special atten- tion with follow-up observations if possible, as such events can lead to new planetary detections. To characterise a new planetary event, high-cadence, accurate observations are optimal. However, without the ability of repeat observations, identification that any event may be planetary needs to happen before it finishes. I have developed a system that automatically retrieves all microlensing survey data and follow-up observations, models the events as single lenses, and publishes the results live to a web site. With minimal human interaction, the modelling system is able to identify and initialize binary events, and perform a thorough search of the seven dimensional parameter space of a binary lens. These results are also presented live through the web site, enabling observers an up to date view of the latest binary solutions. The real-time modelling of the system enables a prompt analysis of ongoing events, providing observers with the information, to determine if further observations are desired for the modelled events. An archive of all modelled binary lens events is maintained and accessible through the website. To date the archive contains 68 unique events’ binary lens solutions from the 2014 observing season. The system developed has been validated through model comparisons of previously published work, and is in use during the current observing season. This year it has played a role in identifying new planetary candidate events, confirming proposed solutions, and providing alternate viable solutions to previously presented solutions.

To date, more than 300 planets orbiting stars other than our sun have been discovered using a range of observing techniques, with new discoveries occuring monthly. The work in this thesis focused on the detection of exoplanets using the transit method. Planets orbiting close to their host stars have a roughly 10 per cent chance of eclipsing (transiting) the star, with Jupiter?sized planets causing a one per cent dip in the flux of the star over a few hours. A wealth of orbital and physical information on the system can be extracted from these systems, including the planet density which is essential in constraining models of planetary formation. To detect these types of planets requires monitoring tens of thousands of stars over a period of months. To accomplish this, we conduct a wide-field survey using the 0.5-meter Automated Patrol Telescope (APT) at Siding Spring Observatory (SSO) in NSW, Australia. Once candidates were selected from the data?set, selection criteria were applied to separate the likely planet candidates from the false?positives. For this thesis, the methods and instrumentation used in attaining data and selecting planet candidates are discussed, as well as the results and analysis of the planet candidates selected from star fields observed from 2004?2007. Of the 65 planet candidates initially selected from the 25 target fields observed, only two were consistent with a planet transit. These candidates were later determined to be eclipsing binary stars based on follow up observations using the 40-inch telescope, 2.3-m telescope, and the 3.9-m Anglo-Australian Telescope, all located at SSO. Additionally, two planet candidates from the SuperWASP-North consortium were observed on the 40-inch telescope. Both proved to be eclipsing binary stars. While no planets were found, our search methods and results are consistent with successful transit surveys targeting similar fields with stars in a similar magnitude range and using similar methods.

Este trabalho consistiu de uma experiência didática que teve como objetivo central desenvolver um material sobre Astronomia, com ênfase em Exoplanetas, motivador e inovador para o ensino de Física. A fim de torná-lo versátil para ser aplicado nas escolas de ensino médio, de fácil manuseio e estudo por parte dos professores que desejarem utilizá-lo com os seus alunos, o material foi organizado na forma de um hipertexto, armazenado em DVD e está disponibilizado na rede. O hipertexto reúne apresentações em PowerPoint, textos de apoio, simulações computacionais, vídeos, sugestões de simulações e vídeos e atividades teórico-práticas, organizados de uma forma que facilita a sua aplicação e o aprendizado do professor que desconhece o assunto, mas que, por outro lado, sente-se motivado em estudá-lo e aplicá-lo junto aos seus alunos. O material foi utilizado numa experiência realizada com alunos do segundo ano do ensino médio no Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Sul – IFRS, Campus Bento Gonçalves, do mês de agosto até meados de dezembro de 2011 e teve como referencial teórico a teoria da aprendizagem significativa de Ausubel, o qual considera o conhecimento prévio do aluno como a variável mais importante na aprendizagem, e a teoria da mediação de Vygotsky, fundamentada na interação social. As avaliações consistiram: (a) de um pré-teste e de um pós-teste, respectivamente, para investigar o conhecimento prévio dos alunos sobre o assunto que foi abordado e para averiguar o quanto a aprendizagem resultou significativa; (b) de duas avaliações, uma no meio e outra ao final da experiência; (c) dos questionários correspondentes às atividades teórico-práticas e, (d) de uma pesquisa de opinião realizada no final do trabalho. Os resultados obtidos foram animadores como pode ser observado: (a) da análise estatística, feita através do “teste t” para dados pareados, entre as respostas do pré-teste e do pós-teste, que indicou significância no aprendizado dos alunos; (b) do desempenho nas duas avaliações realizadas e, (c) das respostas dos alunos à pesquisa de opinião realizada ao final da experiência, que declararam, em sua maioria, terem gostado de estudar Astronomia como tema de contextualização para o estudo da Física. Espera-se que o material desenvolvido e organizado na forma de um hipertexto e os resultados dessa experiência didática motivem os professores a utilizarem tópicos de Astronomia como contexto para o ensino da Física no ensino médio. / This work consisted of a learning experience that aims, as a main goal, to develop a material on Astronomy, with emphasis on Exoplanets, as a motivator and innovator in the teaching of Physics. In order to become versatile to be used in high schools and easy to handle and study by teachers who wish to use it with their students, the material was organized as a hypertext, stored on DVD and is available on network. The hypertext gathers PowerPoint presentations, handouts, computer simulations, videos, tips about video simulations and theoretical-practical activities, organized in a way that facilitates its application and learning of the teacher who doesn’t know the subject, but, on the other hand, feels himself motivated to study it and apply it along to their students. The material was used in an experiment conducted with students in their second year of high school at the Federal Institute of Education, Science and Technology of Rio Grande do Sul – IFRS, Campus Bento Gonçalves, from August to mid-December 2011 and had as theoretical reference Ausubel’s theory of meaningful learning, which considers the student’s prior knowledge as the most important variable in learning, and Vygotsky’s theory of mediation, grounded in social interaction. The avaluations consisted of: (a) a pre-test and a post-test, respectively, to investigate the student’s prior knowledge on the subject that was addressed and to determine how much the learning came to be significant; (b) two assessments, one in the middle and another at the end of the experiment; (c) questionnaires corresponding to theoretical and practical activities, and (d) an opinion survey conducted at the end of the work. The results were encouraging as can be observed: (a) the statistical analysis performed using the “t test” for paired data, the responses between the pre-test and post-test, which indicated significance on student learning; (b) performance on both assessments (two) and (c) the students’ answers to the survey conducted at the end of the experiment, which stated, in most cases, they liked to study Astronomy as a subject of contextualization for the study of physics. It is hoped that the material developed and organized as a hypertext, and the results of this learning experience, motivate teachers to use Astronomy topics as context for teaching physics in high school.

The discovery of exoplanets represents one of the greatest scientific revolutions in history, and exoplanetary science has rapidly become uniquely positioned to address profound questions about the origins of life, and about humanity's place (and future) in the cosmos. Since the discovery of the first exoplanet over two decades ago, the radial velocity (RV) method has been one of the most productive techniques for discovering new planets. It has also become indispensable for characterising exoplanets detected via other techniques, notably transit photometry. Unfortunately, signals intrinsic to stars themselves - especially magnetic activity signals - can induce RV variations that can drown out or even mimic planetary signals. Modelling and thus mitigating these signals is notoriously difficult, which represents a major obstacle to using next-generation instruments to detect lower mass planets, planets with longer periods, and planets around more magnetically-active stars. Enter Gaussian processes (GPs), which have a number of features that make them very well suited to the joint modelling of stochastic activity processes and dynamical (e.g. planetary) signals. In this thesis, I leverage GPs to enable the study of smaller planets around a wider variety of stars than has previously been possible. In particular, I develop a principled and sophisticated Bayesian framework, based on GPs, for modelling RV time series jointly with ancillary activity-sensitive proxies, thus allowing activity signals to be constrained and disentangled from genuine planetary signals. I show that my framework succeeds even in cases where existing techniques would fail to detect planets, e.g. the case of a weak planetary signal with period identical to its host star's rotation period. In a first application of the framework, I demonstrate that Alpha Centauri Bb - until 2016, thought to be the closest exoplanet to Earth, and also the lowest minimum-mass exoplanet around a Sun-like star - was, in fact, an astrophysical false positive. Next, I use the framework to re-characterise the well-studied Kepler-10 system, thereby resolving a mystery surrounding the mass of planet Kepler-10c. I also use the framework to help discover or characterise various exoplanets. Finally, the activity modelling framework aside, I also present in outline form a few promising applications of GPs in the context of modelling stellar signals and studying exoplanets, viz. GPs for (i) enhanced characterisation of stellar rotation; (ii) generating realistic synthetic observations, and modelling in a systematic way the effects of an observing window function; and (iii) ultra-precise extraction of RV shifts directly from observed spectra, without requiring template cross-correlation.

The field of extrasolar planets is undoubtedly one of the most exciting and fast-moving in astronomy. Thanks to the Kepler Space Telescope, which has given us the Kepler and K2 missions, we now have thousands of planets to study and thousands more candidates waiting to be confirmed.For this thesis work, I used K2 data in the form of stellar light curves for Campaign 15 – the 15th observation field of this mission – to search for transiting exoplanets. I present one way to produce a viable list of planetary candidates, which is the first step to exoplanet discovery. I do this by first applying a package of subroutines called EXOTRANS to the light curves. EXOTRANS uses two wavelet-based filter routines: VARLET and PHALET. VARLET is used to remove stellar variability and abrupt discontinuities in the light curve. Since a transit appears box-like, EXOTRANS utilises a box-fitting least-squares algorithm to extract the transit event by fitting a square box. PHALET removes disturbances of known frequencies (and their harmonics) and is used to search the light curve for additional planets. Once EXOTRANS finishes its run, I examine the resulting plots and flag the ones, which contain a transit feature that does not appear to be a false positive. I then perform calculations on the shortlisted candidates to further refine their quality. This resulted in a list of 30 exoplanet candidates. Finally, for eight of them, I used a light curve detrending routine (Exotrending) and another software package, Pyaneti, for transit data fitting. Pyaneti uses MCMC sampling with a Bayesian approach to derive the most accurate orbital and candidate parameters. Based on these estimates and combined with stellar parameters from the Ecliptic Plane Input Catalogue, I comment on the eight candidates and their host stars.However, these comments are only preliminary and speculative until follow-up investigation has been conducted. The most widely used method to do this is the radial velocity method, through which more detailed information is obtained about the host star and in turn, about the candidate. This information, specifically the planetary mass, allows for the bulk density to be estimated, which can give indication about a planet’s composition.Although the Kepler Space Telescope is at the end of its life, new missions with at least a partial focus on exoplanets, are either ongoing (Transiting Exoplanets Survey Satellite – TESS) or upcoming (Characterising Exoplanets Satellite – CHEOPS, James Webb Space Telescope – JWST, Planetary Transits and Oscillations – PLATO). They will add thousands of new planets, providing unprecedented accuracy on the transit parameters and will make significant advances in the field of exoplanet characterisation. The methods used in this work are as applicable to these missions as they have been for the now retired Convection, Rotation et Transits planétaires (CoRoT) – the first space mission dedicated to exoplanet research, and Kepler.

Depuis la découverte de la première exoplanète en 1995 par Mayor et Queloz, le nombre de planètes extrasolaires découvertes n'a cessé d'augmenter, pour dépasser les 1000 planètes à la fin de l'année 2013. Depuis le début des années 2000, la détection s'est accompagnée d'une volonté de caractérisation de l'atmosphère des exoplanètes. Les méthodes utilisées jusqu'ici sont la spectroscopie de transit primaire et l'étude des émissions thermiques en transit secondaire ou via l'étude des courbes de phase. L'objet de cette thèse s'inscrit dans cette recherche de caractérisation des atmosphères exoplanétaires, en s'intéressant à une méthode jusqu'ici inexplorée : l'analyse des émissions thermosphériques, i.e. les émissions de la haute atmosphère induites par les entrées énergétiques, flux extrême UV de l'étoile hôte et précipitations électroniques principalement. La première partie de cette thèse s'intéresse aux émissions thermosphériques de la Terre primitive avec une approche basée sur la modélisation. Le but étant la détermination des différentes émissions de la Terre à travers son histoire, afin de disposer de proxies pour la recherche et la caractérisation d'exoplanètes telluriques. Dans un premier temps nous avons calculé l'émission de l'atmosphère primordiale de la Terre irradiée par le Soleil jeune dans la raie Lyman Alpha. Nous avons montré que la raie planétaire, principalement formée par diffusion cohérente, montre un rapport d'émission avec le Soleil de l'ordre de 10-8, inaccessible aux observations, avec les instruments actuels ou de prochaine génération. Ce premier résultat nous à conduit à étudier la faisabilité d'une méthode indirecte de détection d'une couronne dense d'hydrogène autour d'une planète tellurique possédant une atmosphère de CO2 par les émissions des sous-produits de dissociation et d'ionisation de CO2. Les calculs menés sur la raie verte de l'oxygène (état O1S) et le doublet UV de CO2+ (état B2Σu+) ont montré que ces émissions présentaient des contrastes de l'ordre de 10^-12 avec le Soleil dans le cas d'une Terre primitive, et de l'ordre de 10^-6-10^-8 pour une planète tellurique proche d'une naine M. La conclusion générale des ces investigations est que les raies fines (atomiques ou moléculaires) des émissions thermosphériques sont trop faibles pour être détectées par les instruments actuels. Une voie possible serait l'étude des bandes d'émission moléculaires, qui nécessite une meilleure compréhension de la distribution en intensité des différentes bandes à travers le spectre, compréhension qui passe par l'étude expérimentale de ces émissions. C'est dans ce cadre que se situe la deuxième partie de cette thèse, qui s'intéresse à l'analyse spectroscopique de la Planeterrella, simulateur d'aurores boréales initialement développé à des fins pédagogiques. Nous avons réalisé une étude spectroscopique à basse et haute résolution de l'air, afin de caractériser les émissions présentes dans l'expérience d'une part, et aussi de disposer d'un spectre de référence qui servira à terme de test pour un code Monte Carlo développé pour étudier le dispositif expérimental, la caractérisation du dispositif constituant une étape nécessaire pour faire de la Planeterrella un objet d'étude scientifique. Enfin, la spectroscopie basse résolution du CO2 a été réalisée, avec des applications potentielles à Mars. / Since the discovery of the first exoplanet in 1995 by Mayor and Queloz, the number of extrasolar planets discovered has continuously grown up, to overtake 1000 planets at the end of 2013. Since the beginning of the 2000's, came with the detection the will to characterize the atmospheres of these exoplanets. Until now, the methods used are the primary transit spectroscopy and the study of the thermal emissions in secondary transit or using phase curves. The purpose of this thesis belongs to that search for characterizing exoplanetary atmospheres, by looking at a method unexplored until now: the study of the thermospheric emissions, i.e. emissions from the upper atmosphere induced by the energetic entries, mainly the extreme UV flux and the electronic precipitations. The first part of this thesis concerns the thermospheric emissions of the primitive Earth with an approach based on modeling. The goal is the determination of the several emissions of the Earth through its history in order to have proxies for the search and the characterization of telluric exoplanets. Initially we calculated the emission of the primary atmosphere of the early Earth under the young Sun in the Lyman Alpha line. We showed that the planetary line in mainly due to coherent diffusion and that the emission ratio between the planet and the Sun in this line is of about 10-8, far from the capabilities of current or next generation instruments. This first result lead us to study the feasibility of an indirect method to infer the presence of dense hydrogen corona surrounding a telluric planet with a CO2-dominated atmosphere, by studying its influence on the emissions of two CO2 by-products. The calculations carried out on the oxygen green line (O1S state) and the UV doublet of CO2+ (B2Σu+ state) showed that theses emissions present contrasts of about 10^-12 with the young Sun in the case of a primitive Earth, and of about 10^-6-10^-8 for a close-in telluric planet around a M dwarf. The general conclusion of the investigations is that the thermospheric emissions of thin (atomic or molecular) lines are too weak to be detected. A possible way could be the study of the molecular bands, of which emissions need to be better understood, especially concerning the intensity distribution of the several bands through the spectrum. This comprehension implies experimental studies of these emissions. The second part of this thesis lies in this scope and concerns the spectroscopic analysis of the Planeterrella, an aurora borealis simulator initially designed for outreach purpose. We made a spectroscopic study at low and high resolution with air, in order to characterize the emissions existing in the experiment, and also to have a reference spectrum which will be a final test for a Monte Carlo code developed to study the experimental device, the characterization of this device being a necessary step for the Planeterrella to become suitable for scientific purpose. Finally, we made a low resolution spectroscopic study of carbon dioxide, with potential applications to Mars.

Este trabalho consistiu de uma experiência didática que teve como objetivo central desenvolver um material sobre Astronomia, com ênfase em Exoplanetas, motivador e inovador para o ensino de Física. A fim de torná-lo versátil para ser aplicado nas escolas de ensino médio, de fácil manuseio e estudo por parte dos professores que desejarem utilizá-lo com os seus alunos, o material foi organizado na forma de um hipertexto, armazenado em DVD e está disponibilizado na rede. O hipertexto reúne apresentações em PowerPoint, textos de apoio, simulações computacionais, vídeos, sugestões de simulações e vídeos e atividades teórico-práticas, organizados de uma forma que facilita a sua aplicação e o aprendizado do professor que desconhece o assunto, mas que, por outro lado, sente-se motivado em estudá-lo e aplicá-lo junto aos seus alunos. O material foi utilizado numa experiência realizada com alunos do segundo ano do ensino médio no Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Sul – IFRS, Campus Bento Gonçalves, do mês de agosto até meados de dezembro de 2011 e teve como referencial teórico a teoria da aprendizagem significativa de Ausubel, o qual considera o conhecimento prévio do aluno como a variável mais importante na aprendizagem, e a teoria da mediação de Vygotsky, fundamentada na interação social. As avaliações consistiram: (a) de um pré-teste e de um pós-teste, respectivamente, para investigar o conhecimento prévio dos alunos sobre o assunto que foi abordado e para averiguar o quanto a aprendizagem resultou significativa; (b) de duas avaliações, uma no meio e outra ao final da experiência; (c) dos questionários correspondentes às atividades teórico-práticas e, (d) de uma pesquisa de opinião realizada no final do trabalho. Os resultados obtidos foram animadores como pode ser observado: (a) da análise estatística, feita através do “teste t” para dados pareados, entre as respostas do pré-teste e do pós-teste, que indicou significância no aprendizado dos alunos; (b) do desempenho nas duas avaliações realizadas e, (c) das respostas dos alunos à pesquisa de opinião realizada ao final da experiência, que declararam, em sua maioria, terem gostado de estudar Astronomia como tema de contextualização para o estudo da Física. Espera-se que o material desenvolvido e organizado na forma de um hipertexto e os resultados dessa experiência didática motivem os professores a utilizarem tópicos de Astronomia como contexto para o ensino da Física no ensino médio. / This work consisted of a learning experience that aims, as a main goal, to develop a material on Astronomy, with emphasis on Exoplanets, as a motivator and innovator in the teaching of Physics. In order to become versatile to be used in high schools and easy to handle and study by teachers who wish to use it with their students, the material was organized as a hypertext, stored on DVD and is available on network. The hypertext gathers PowerPoint presentations, handouts, computer simulations, videos, tips about video simulations and theoretical-practical activities, organized in a way that facilitates its application and learning of the teacher who doesn’t know the subject, but, on the other hand, feels himself motivated to study it and apply it along to their students. The material was used in an experiment conducted with students in their second year of high school at the Federal Institute of Education, Science and Technology of Rio Grande do Sul – IFRS, Campus Bento Gonçalves, from August to mid-December 2011 and had as theoretical reference Ausubel’s theory of meaningful learning, which considers the student’s prior knowledge as the most important variable in learning, and Vygotsky’s theory of mediation, grounded in social interaction. The avaluations consisted of: (a) a pre-test and a post-test, respectively, to investigate the student’s prior knowledge on the subject that was addressed and to determine how much the learning came to be significant; (b) two assessments, one in the middle and another at the end of the experiment; (c) questionnaires corresponding to theoretical and practical activities, and (d) an opinion survey conducted at the end of the work. The results were encouraging as can be observed: (a) the statistical analysis performed using the “t test” for paired data, the responses between the pre-test and post-test, which indicated significance on student learning; (b) performance on both assessments (two) and (c) the students’ answers to the survey conducted at the end of the experiment, which stated, in most cases, they liked to study Astronomy as a subject of contextualization for the study of physics. It is hoped that the material developed and organized as a hypertext, and the results of this learning experience, motivate teachers to use Astronomy topics as context for teaching physics in high school.

The study of magnetic fields on low-mass stars is important due to their ubiquity. They are responsible for phenomena spanning a wide range of spatial and temporal scales. Over the last two decades, the Zeeman-Doppler imaging (ZDI) technique has been used to study the topologies of stellar magnetic fields. A great deal has been learnt about how the magnetic characteristics of cool dwarfs vary as a function of parameters such as mass, rotation or age. In this thesis, I assemble a sample of stars with Zeeman-Doppler maps. I study their poloidal and toroidal components as a function of fundamental parameters and also in relation to activity cycles. I find that the relationship between poloidal and toroidal fields is different for stars above and below the fully convective boundary, in line with previous ZDI studies. I also find that the fields of strongly toroidal stars must be generated axisymmetrically. With regards to activity cycles, I find that so called “inactive branch" stars appear to remain poloidal throughout their activity cycle while so called “active branch" stars appear to be able to generate strong toroidal fields. Magnetic activity can also interact with exoplanets that may be orbiting a star. In this thesis, I consider two such interactions. The first is the compression of planetary magnetospheres by stellar winds. Sufficiently powerful winds can strip a planet of its atmosphere and render it uninhabitable. However magnetospheric shielding can provide some protection. I show that planets around 0.6 M⊙ - 0.8 M⊙ stars are the most likely to be able to protect their atmospheres. The second interaction I consider is exoplanetary radio emission. I present a wind model and show that exoplanetary radio emissions will depend strongly on the structure of the magnetic field structure of the central star.