Program: GN-2023B-Q-227

Hot and ultra-hot Jupiters (HJs and UHJs) are key targets to study planetary atmospheres in extreme regimes. Due to their high temperatures, they offer the unique opportunity to probe key atmospheric properties through the study of refractory elements, at high signal to noise. We propose the first homogeneous survey of the optical emission spectra of the day-side of 8 HJs and UHJs, to measure: (1) their thermal structures and (2) abundances of atomic and molecular refractory species (e.g. Fe, Fe+, Ti, Ti+, TiO), strong optical absorbers likely responsible of thermal inversions in hot planets. We will cover 2,500 K in planet equilibrium temperature, and 2 orders of magnitude in gravity, looking for trends of our observables along these axes. We will thus tackle outstanding questions on the thermal structures and compositions of hot Jupiters to realize the potential of this class of planets. Ours is one of the first homogeneous surveys of planetary spectra, and the first survey of high spectral resolution, optical emission spectra of HJS and UHJs, and complements space-born efforts with HST and Spitzer to higher spectral resolution and different wavelengths. The legacy of this program is a library of optical spectra, which will complement infrared observations from JWST and form the basis for the interpretation of JWST observations of the hottest giant planets.