The Hot Neptune WASP-166 b with ESPRESSO II: Confirmation of atmospheric sodium

TL;DR

This study confirms the detection of sodium in the atmosphere of the hot Neptune WASP-166b using ESPRESSO, providing insights into atmospheric composition within the Neptune desert and emphasizing the importance of spectral analysis techniques.

Contribution

It provides the first confirmed resolved sodium detection in a Neptune desert exoplanet using ESPRESSO, improving upon previous tentative observations with HARPS.

Findings

Confirmed sodium detection in WASP-166b's atmosphere.

Detected line broadening indicating atmospheric dynamics.

Highlighted importance of analyzing low-SNR spectral regions.

Abstract

The hot Neptune desert, a distinct lack of highly irradiated planets in the size range of Neptune, remains one of the most intriguing results of exoplanet population studies. A deeper understanding of the atmosphere of exoplanets sitting at the edge or even within the Neptune desert will allow us to better understand if planetary formation or evolution processes are at the origin of the desert. A detection of sodium in WASP-166b was presented previously with tentative line broadening at the 3.4 sigma with the HARPS spectrograph. We update this result with two transits observed with the ESPRESSO spectrograph, confirming the detection in each night and the broadened character of the line. This result marks the first confirmed resolved sodium detection within the Neptune desert. In this work, we additionally highlight the importance of treating low-SNR spectral regions, particularly where absorption lines of stellar sodium and planetary sodium overlap at mid-transit - an important caveat for future observations of the system.