From Space to Ground: Characterising Exoplanet Atmospheres at Low and High Spectral Resolutions

In recent years, the Hubble Space Telescope has pioneered spectroscopic studies of exoplanet atmospheres at low-resolution, with ground-based spectrographs having substantially contributed too (e.g. FORS2/VLT). Distant worlds have been characterised, from hot and evaporating Jupiter-like planets, to rocky lava worlds, to potentially habitable terrestrial planets. Thanks to the WFC3 and STIS instruments aboard HST, molecules such as water vapour, sodium, potassium, titanium and vanadium oxide have been detected. Some exoplanets were also found to possess a thick layer of clouds, which reduced the size of their spectral features or impeded their atmospheric characterisation altogether. Using archive data taken with HST/STIS,
HST/WFC3 and Spitzer/IRAC, I investigated the atmosphere of WASP-17 b, an inflated hot-Jupiter. My results confirm the presence of water vapour, a molecule commonly found in exoplanet atmospheres, and possible traces of aluminium oxide and titanium hydride. The best retrieval model also suggest a strong stellar contamination on the spectrum of WASP-17 b. However, a F6-type host star such as this is not expected to display strong photospheric activity. Following the recent adaptation of the Iraclis pipeline to be able to analyse data from any instrument on HST and JWST, further observations of WASP-17 b will confirm or refute my findings, while expanding our knowledge on exoplanetary atmospheres at much wider wavelength regimes.

At high spectral resolutions, state-of-the-art techniques focus on finding atomic and molecular signatures in the atmosphere of transiting and non-transiting exoplanets. From the ground, spectrographs like CRIRES+/VLT or HARPS-N/TNG employ the radial-velocity method to detect the planet's Doppler shifted signal as it orbits its host star. By disentangling the exoplanet spectral lines from the telluric and stellar features, we are able to recover the molecules present in the exo-atmosphere by cross-correlating the planetary extracted spectrum with molecular cross-sections at high resolutions. Thanks to the collaboration with the University of Palermo and INAF-Palermo, I have access to a large collection of HARPS-N data sets, through which I am characterising the upper atmosphere of the ultra-hot Jupiter KELT-9b. This study will not only be paramount to the characterisation of atmospheric winds but also to constrain the planet's mass-loss rate.