The Citizen Continental-America Telescopic Eclipse (CATE) Experiment established a standardized set of observation procedures and 72 volunteer observation teams with identical equipment along the path of the 2017 total solar eclipse. CATE successfully imaged the solar corona from 66 of the 72 observation sites resulting in a high dynamic range animation of 90 minutes of solar corona data collected by volunteer citizen science teams. A subgroup of CATE began work in the fall of 2017 to evaluate use of the standard CATE observation setup for exoplanet transit observations. Light curves and analysis of data using AstroImageJ of two well know transiting exoplanets, HD209458b (V = 7.65, depth = 1.5%) and HD189733b (V= 7.67, depth=2.4%) are presented along with modifications to CATE telescopes required for successful exoplanet follow up observations.

2023 / The L and T spectral types extend the traditional Harvard stellar classification system to include objects that are less massive, cooler, and spectroscopically distinct from the latest M dwarfs. L and T dwarfs span the transition from the stellar regime to that of brown dwarfs and planets and were a missing component of the stellar classification sequence until the proliferation of near-infrared (NIR) array detectors, which probe the wavelengths where L and T dwarfs give off the majority of their flux (∼1−2.5 μm). For the same reason, L and T dwarfs remain a mostly unexplored parameter space for exoplanet surveys, which have traditionally been performed at optical wavelengths. Predictions differ as to whether or not L and T dwarfs host a significant population of short-period super-Earth and mini-Neptune planets, a tension that can only be resolved by searching for satellites around L and T dwarfs. In this dissertation, I report the results of just such a survey: the Perkins INfrared Exosatellite Survey (PINES). PINES is a NIR search for transiting satellites around L and T dwarfs and it represents the largest photometric monitoring campaign of L and T dwarfs, to date. I describe the design of the survey, its implementation on Boston University's 1.83-m Perkins Telescope Observatory, and its ongoing operation, which has yielded light curves of over 130 L and T dwarfs. I present a systematic search for transit events in these light curves. I found one plausible candidate, which, if confirmed, would represent the first transiting planet discovered around a brown dwarf and would point to enhanced planet occurrence rates for L and T dwarfs compared to earlier-type stars. Finally, I investigated the potential for detecting transiting planets around L and T dwarfs with the upcoming Nancy Grace Roman Space Telescope, which will perform a large-scale time domain survey of the Galactic bulge at NIR wavelengths. I show that this survey will detect few transiting planets around L and T dwarfs (if any) and that ground-based surveys like PINES will remain the best options for discovering such planets in the coming decade.

Parmi les méthodes qui permettent de détecter des exoplanètes, la photométrie des transits est celle qui a connu le plus grand essor ces dernières années grâce à l’arrivée des télescopes spatiaux CoRoT (en 2006) puis Kepler (en 2009). Ces deux satellites ont permis de détecter des milliers de transits potentiellement planétaires. Étant donnés leur nombre et l’effort nécessaire à la confirmation de leur nature, il est essentiel d’effectuer, à partir des données photométriques, un classement efficace permettant d’identifier les transits les plus prometteurs et qui soit réalisable en un temps raisonnable. Pour ma thèse, j’ai développé un outil logiciel, rapide et automatisé, appelé BART (Bayesian Analysis for the Ranking of Transits) qui permet de réaliser un tel classement grâce une estimation de la probabilité que chaque transit soit de nature planétaire. Pour cela, mon outil s’appuie notamment sur le formalisme bayésien des probabilités et l’exploration de l’espace des paramètres libres par méthode de Monte Carlo avec des chaînes de Markov (mcmc).Une fois les exoplanètes détectées, l’étape suivante consiste à les caractériser. L’étude du système solaire nous a démontré, si cela était nécessaire, que l’information spectrale est un point clé pour comprendre la physique et l’histoire d’une planète. L’interférométrie annulante est une solution technologique très prometteuse qui pourrait permettre cela. Pour ma thèse, j’ai travaillé sur le banc optique Nulltimate afin d’étudier la faisabilité de certains objectifs technologiques liés à cette technique. Au-delà de la performance d’un taux d’extinction de 3,7.10^-5 en monochromatique et de 6,3.10^-4 en polychromatique dans l’infrarouge proche, ainsi qu’une stabilité de σN30 ms = 3,7.10^-5 estimée sur 1 heure, mon travail a permis d’assainir la situation en réalisant un budget d’erreur détaillé, une simulation en optique gaussienne de la transmission du banc et une refonte complète de l’informatique de commande. Tout cela m’a finalement permis d’identifier les faiblesses de Nulltimate. / From all exoplanet detection methods, transit photometry went through the quickest growth over the last few years thanks to the two space telescopes, CoRoT (in 2006) and Kepler (in 2009). These two satellites have identified thousands of potentially planetary transits. Given the number of detected transits and the effort required to demonstrate their natures, it is essential to perform, from photometric data only, a ranking allowing to efficiently identify the most promising transits within a reasonable period of time. For my thesis, I have developed a quick and automated software called bart (Bayesian Analysis for the Ranking of Transits) which realizes such a ranking thanks to the estimation of the probability regarding the planetary nature of each transit. For this purpose, I am relying on the Bayesian framework and free parameter space exploration with Markov Chain Monte Carlo (mcmc) methods.Once you have detected exoplanets, the following step is to characterise them. The study of the solar system demonstrated, if it was necessary, that the spectral information is a crucial clue for the understanding of the physics and history of a planet. Nulling interferometry is a promising solution which could make this possible. For my thesis, I worked on the optical bench Nulltimate in order to study the feasibility of certain technological requirements associated with this technique. Beyond the obtention of a nulling ratio of 3,7.10^-5 in monochromatic light and 6,3.10^-4 in polychromatic light in the near infrared, as well as a stability of σN30 ms = 3,7.10^-5 estimated on 1 hour, my work allowed to clarify the situation thanks to a detailed error budget, a simulation of the transmission based on Gaussian beam optics and a complete overhaul of the computer control system. All of this finally resulted in the identification of the weaknesses of Nulltimate.