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Development and Application of Tools to Characterize Transiting Astrophysical Systems

Since the discovery of the first exoplanets more than 20 years ago, there has been an increasing need for photometric and spectroscopic models to characterize these systems. While imaging has been used extensively for Solar System bodies and extended objects like galaxies, the small angular extent of typical planetary systems makes it difficult or impossible to resolve them. Spatially integrated observations like measuring the total brightness or spectrum, however, can be conducted at a resonable cost. This thesis focuses on photometric models in the context of transiting systems, which exhibit a number of phenomena that can be exploited for characterization. First, we showcase the popular methods of transiting exoplanet discovery and characterization by ground based observations on the hot Jupiter HAT-P-27b. We demonstrate how transits allow us to constrain planetary mass, radius, and orbital inclination, which would not be possible based only on, for example, radial velocity measurements. Next, we perform reflection spectroscopy on HAT-P-1b, another hot Jupiter, using the binary companion of the host star as a reference to remove systematic errors from the signal. Here the transiting nature of the system allows us to look for the very faint light reflected by the planet. We also apply the idea of planetary transits to investigate the feasibility of transit observations in astrophysical systems of very different scale: stars in galactic nuclei potentially transiting the accretion disk of the supermassive black hole in the galactic center. Finally, we focus on mapping spots on the stellar surface using transits. This method has been used for a decade, and helped constrain stellar rotation or orbital geometry in a number systems. We study starspots on HAT-P-11 to learn more about stellar rotation and to investigate the size and contrast of the spots themselves.