Exoplanet atmospheres at high resolution through a modest-size telescope. Fe II in MASCARA-2b and KELT-9b with FIES on the Nordic Optical Telescope

TL;DR

This study demonstrates that modest-size telescopes equipped with high-resolution spectrographs like FIES can effectively detect and analyze atomic species such as Fe II in the atmospheres of ultra-hot Jupiters, expanding atmospheric characterization capabilities beyond large telescopes.

Contribution

It shows the feasibility of using a 2.56-meter telescope with FIES for exoplanet atmospheric studies, specifically detecting Fe II in ultra-hot Jupiters, which was previously mainly done with larger telescopes.

Findings

Fe II detected in MASCARA-2 b with 4.5σ and 4.0σ significance.

Fe II detected in KELT-9 b with 8.5σ significance.

Moderate blueshift observed in KELT-9 b indicating high-velocity winds.

Abstract

Ground-based, high-resolution spectrographs are providing us with an unprecedented view of the dynamics and chemistry of the atmospheres of planets outside the Solar System. While there is a large number of stable and precise high-resolution spectrographs on modest-size telescopes, it is the spectrographs at observatories with apertures larger than 3.5 metres that dominate the atmospheric follow-up of exoplanets. In this work, we explore the potential of characterising exoplanetary atmospheres with FIES, a high-resolution spectrograph at the 2.56 metre Nordic Optical Telescope. We observed two transits of MASCARA-2 b (also known as KELT-20 b) and one transit of KELT-9 b to search for atomic iron, a species that has been recently discovered in both neutral and ionised forms in the atmospheres of these ultra-hot Jupiters using large telescopes. Using a cross-correlation method, we detect a signal of Fe II at the $4.5\sigma$ and $4.0\sigma$ level in the transits of MASCARA-2 b. We also detect Fe II in the transit of KELT-9 b at the $8.5\sigma$ level. Although we do not find any significant Doppler shift in the signal of MASCARA-2 b, we do measure a moderate blueshift (3-6 km/s) of the feature in KELT-9 b, which might be a manifestation of high-velocity winds transporting Fe II from the planetary dayside to the nightside. Our work demonstrates the feasibility of investigating exoplanet atmospheres with FIES, potentially unlocking a wealth of additional atmosphere detections with this and other high-resolution spectrographs mounted on similar-size telescopes.