Titanium chemistry in WASP-121 b revealed by high-resolution day-side spectroscopy

Ultra-hot Jupiters form a new class of exoplanets that tend to orbit hot early type stars in short periods, and may be heated to temperatures much greater than 2,000K on their day-sides. The extreme temperature dissociates all but the most strongly bound molecules and a significant fraction of the atomic gas may be thermally ionised. Under these circumstances, line absorption lines by metals and some molecules are dominant sources of short-wave opacity, causing strong thermal inversions. These inversions have consequences for atmospheric chemistry, as well as global circulation of gas and heat. Excitingly, due to the highly elevated temperatures, thermal inversion layers cause strong emission lines, that can be observed using high-resolution spectroscopy. This allows the chemical and thermal structure of the atmospheric to be constrained, in principle in three dimensions. 

 

Previous transit observations of the ultra-hot Jupiter WASP-121 b have revealed a rich spectrum of various metals, including iron and vanadium, but with a notable absence of titanium and titanium-oxide, which may be depleted due to condensation processes. In this talk I will present our recent observations of the emission spectrum of the planet’s dayside, which, beside showing a collection of emitting metals, provide strong direct evidence of the fate of titanium-bearing species on the cooler night-side of the planet (Fig. 1).

 

 

Fig. 1: