Metals in the emission spectrum of Kelt-9b

Ultra-hot Jupiters are planets hotter than 2,200 K, that thus offer the opportunity to study the physics and chemistry of planetary atmospheres in a regime that is not accessible in the solar system or in other exoplanets. At such temperatures, molecules begin to dissociate and atoms become ionized, which gives rise to opacity sources such as H- or metal lines. Indeed, recent transmission spectroscopy observations at high resolution (R>100,000) revealed for the first time lines from metals in the atmosphere of the hottest planet of this category: KELT-9b (4,000 K). These observations probe the terminator of the planet, at the transition between its permanent dayside and its permanent nightside. While they offer the first glimpse in the refractory component of the composition of a planet, these observations are difficult to interprete due to the uncertainty in the thermal conditions at the day-night transition region. In this talk, we present a set of complementary observations of Kelt-9b that target the light directly emitted from its dayside. We report a detection of metal lines in emission, and discuss the techniques used and our interpretation of the observations. In combination with the existing transmission spectroscopy data, our observations provide the chance to map the 3D structure of the planet.