| Riassunto: | <p>Extrasolar planets (exoplanets) are planetary-mass objects that orbit different stars in our galaxy. To date, there have been over 4000 of these objects discovered, with a bias towards objects that transit their host star. This thesis focuses on interpreting the emission spectra of hot to ultra-hot Jupiter exoplanets. These are Jupiter-sized objects which orbit close to their host star, resulting in high effective temperatures and a tidally-locked orbital configuration.</p>
<p>The study of the emission spectra of exoplanets lets us probe the vertical chemical and thermal structure of the planet's atmosphere. The majority of the current observations are of hot to ultra-hot Jupiter planets, as the day-side flux is readily measurable with current telescopes. Therefore the first part of the thesis focuses on upgrading the NEMESIS model to calculate H$^{-}$ opacities and implementing a temperature-pressure parameterisation that can handle temperature profiles that can span the parameter space that contain non-inverted and inverted profiles.</p>
<p>These objects exhibit large day-night contrasts due to their tidally-locked nature, and it has been shown that this is detectable with current observations. We explore in this thesis the biases that can arise when studying an exoplanet with a non homogeneous thermal structure. We find that if we assume the thermal structure to be uniform on the disc, this can lead to spurious detection of molecules. We show that by retrieving the nightside and the dayside of the planet simultaneous we can perform an unbiased retrieval. We find that if the nightside contribution is small enough, a simple dilution factor can be used to account for the spatial inhomogeneity of the atmosphere.</p>
<p>Finally, we explore how scattering clouds can affect the way we interpret the emission spectra of cloudy exoplanets. We show that using a model that does not contain scattering to study the emission spectra of a cloudy exoplanet can lead to incorrectly inferred chemical abundances and also an erroneous detection of a thermal inversion. To provide a more agnostic approach to the modelling of clouds, in this thesis we have developed a novel technique to retrieve the cloud scattering properties, namely the single scattering albedo, which approximately encapsulates the real and imaginary refractive index spectra and the particle size of the cloud condensing species.</p>
<p>This thesis has broader impacts on the exoplanet community. The tools developed for hot and large planets will ensure that when moving to study smaller and cooler objects in the future, we can trust that our techniques are well verified.</p>
|
|---|