The GAPS Programme at TNG XXXIII. HARPS-N detects multiple atomic species in emission from the dayside of KELT-20b

TL;DR

This study confirms temperature inversions in the atmospheres of ultra-hot Jupiters orbiting A-type stars by detecting multiple atomic emission lines, including the first emission detection of CrI in an exoplanet atmosphere.

Contribution

It presents the first detection of CrI emission in an exoplanet atmosphere and demonstrates the use of atomic emission lines to characterize thermal inversions.

Findings

Detected FeI, FeII, and CrI emission lines in KELT-20b's atmosphere.

CrI emission detected for the first time in an exoplanet atmosphere.

Evidence of different atmospheric properties before and after occultation.

Abstract

The detection of lines in emission in planetary atmospheres provides direct evidence of temperature inversion. We confirm the trend of ultra-hot Jupiters orbiting A-type stars showing temperature inversions on their daysides, by detecting metals emission lines in the dayside of KELT-20b. We first detect the planetary emission by using the G2 stellar mask of the HARPS-N pipeline, which is mainly composed of neutral iron lines, as a template. Using neutral iron templates, we perform a retrieval of the atmospheric temperature-pressure profile of the planet, confirming a thermal inversion. Then we create models of planetary emission of different species using the retrieved inverted temperature-pressure profile. By using the cross-correlation technique, we detect FeI, FeII and CrI at signal-to-noise ratio levels of 7.1, 3.9 and 3.6, respectively. The latter is detected for the first time in emission in the atmosphere of an exoplanet. Contrary to FeI, FeII and CrI are detected only after the occultation and not before, hinting for different atmospheric properties in view on the pre- and post- occultation orbital phases. A further retrieval of the temperature-pressure profile performed independently on the pre- and post- occultation phases, while not highly significant, points to a steeper thermal inversion in the post-occultation.