PhD thesis defense by Azzurra d'Alessandro

The defense has been confirmed to start at 14:00 hrs. 

Zoom link for the defense: https://ucph-ku.zoom.us/j/61109098443.

Title: Exoplanetary atmospheres, spectrum computations, and temperature inversions

Abstract: Despite being a relatively young field, the study of exoplanets has rapidly become one of the most active and widely-researched areas in astrophysics. A large variety of exoplanets have been discovered, each offering unique insights into planetary formation and evolution. However, due to their relative ease of detection and the wealth of data they provide, highly irradiated gas giants, known as “Hot Jupiters”, remain the most extensively studied.

Hot Jupiters are located in close-in orbits around their parent stars, receiving an intense amount of irradiation. When strong optical/ultraviolet absorbers like TiO and VO are present in a Hot Jupiter’s atmosphere, they are expected to heat the gas, leading to a temperature increase with altitude, known as a thermal inversion. While this feature has been observed in some cases, it is not as widespread as initially predicted. The mechanisms that regulate the presence and intensity of thermal inversions, as well as the specific chemicals responsible, remain subjects of ongoing debate.

This thesis provides new insights into the problem through simulations of Hot Jupiter atmospheres using a 1D self-consistent model. The MARCS + Static Weather + GGChem (MSG) code is employed to simulate the atmospheric structure of a Hot Jupiter at the sub-stellar point, complemented by the spectral synthesis code syntos. Originally developed as a post- processing tool for MARCS, syntos is upgraded in this work to model the spectra of irradiated exoplanets. The combination of MSG and syntos forms a robust tool for describing the atmospheric structure and spectrum of Hot Jupiters at the sub-stellar point.

A case study is developed by comparing model atmospheres with and without TiO and VO, exploring various metallicities for both scenarios. In the TiO/VO-rich models, multiple C/O ratios are examined. The study explores how these factors influence temperature inversions, finding that inversions occur either in the presence of TiO and VO at solar metallicity or in their absence at sub-solar metallicity. Changes in the C/O ratio alter the concentrations of carbon- and oxygen-bearing compounds, which in turn affect the shape and intensity of the temperature inversions and the molecules responsible for them. The different spectral signatures characterizing these cases may not be discernible by the Hubble and Spitzer telescopes; however, the James Webb Space Telescope will be able to detect these signatures with high confidence and distinguish between the different cases.

The findings in this thesis contribute to a deeper understanding of exoplanetary atmospheres, particularly the mechanisms driving thermal inversions, offering valuable insights for future exoplanet characterization.

Supervisor: Uffe Gråe Jørgensen

PhD defense committee:

Peter Ditlevsen, PICE/NBI (chair)

Jens Hoeijmakers, Lund Universtiy

Paul Mollière, Max Planck Institute for Astronomy