Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b

TL;DR

This paper reports the first direct detection of atomic iron and titanium ions in the atmosphere of the ultra-hot exoplanet KELT-9b, providing insights into its atmospheric composition and chemistry.

Contribution

It presents the first direct detection of atomic Fe, Fe+, and Ti+ in an exoplanet atmosphere using high-resolution spectroscopy during transit.

Findings

Detected atomic Fe and Fe+ in KELT-9b's atmosphere

Detected Ti+ in KELT-9b's atmosphere

Confirmed high-temperature, cloud-free atmospheric chemistry

Abstract

The chemical composition of an exoplanet is a key ingredient in constraining its formation history. Iron is the most abundant transition metal, but has never been directly detected in an exoplanet due to its highly refractory nature. KELT-9b (HD 195689b) is the archetype of the class of ultra-hot Jupiters that straddle the transition between stars and gas-giant exoplanets and serve as distinctive laboratories for studying atmospheric chemistry, because of its high equilibrium temperature of 4050 +/- 180 K. These properties imply that its atmosphere is a tightly constrained chemical system that is expected to be nearly in chemical equilibrium and cloud-free. It was previously predicted that the spectral lines of iron will be detectable in the visible range of wavelengths. At these high temperatures, iron and several other transition metals are not sequestered in molecules or cloud particles and exist solely in their atomic forms. Here, we report the direct detection of atomic neutral and singly-ionized iron (Fe and Fe+), and singly-ionized titanium (Ti+) in KELT-9b via the cross-correlation technique applied to high-resolution spectra obtained during the primary transit of the exoplanet.