Unveiling exoplanet atmospheres with the ACCESS survey

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In this thesis, we present the first results of a survey aimed at the detection of exoplanet atmospheres from the ground using the technique of transmission spectroscopy: the Arizona CfA-Católica Exoplanet Spectroscopy Survey (ACCESS), a multi-institutional effort aimedat the detection of optical features in giant exoplanet atmospheres. The survey is currently being carried out using the Inamori-Magellan Areal Camera and Spectrograph (IMACS) mounted on the Magellan Baade 6.5m telescope at Las Campanas Observatory, Chile, an instrument not designed (or comissioned) for the precise observations requiered to detect these signatures on these distant worlds, this thesis presents the first detailed comissioningand validation of this instrument for such observations, for which a special data reduction pipeline had to be created and which is today used routinely by the group. In this work we also present a detailed analysis of important stellar astrophysical effects that impact on the observed light curve of a transiting exoplanet, which is what is used in practice to extract the signatures of atomic and/or molecular features in the atmospheres of exoplanets using the technique of transmission spectroscopy. In particular, we present two detailed works published in the context of this thesis on the effect of limb-darkening, a fundamental effect observed during the transit of an exoplanet in front of a star, in which we detail how this effect impacts on the retrieved transit parameters, how well we actually understand this effect and how to optimally analyze a transit light curve using the “best" parametrization forit, avoiding in this way any biases that might arise from an incorrect treatment of the effect.
Tesis (Doctor of Philosophy)--Pontificia Universidad Católica de Chile, 2017