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

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 temperaturepressure 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 Fe i, Fe ii and Cr i at signal-tonoise 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 Fe i, Fe ii and Cr i 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.

The PEPSI-LBT Exoplanet Transit Survey (PETS). II. A Deep Search for Thermal Inversion Agents in KELT-20 b/MASCARA-2 b with Emission and Transmission Spectroscopy

“…We note that these results are contingent upon the choice of P-T profile, as the strength of the inversion affects the strength of the emission lines, and thus the inferred VMR limit. However, Yan et al (2022b), Fu et al (2022), and Borsa et al (2022 all independently retrieved broadly similar P-T profiles using independent methodology and data, giving us some confidence in the broad accuracy of our P-T profile. Additionally, the presence of additional or stronger continuum opacity sources than we have assumed could affect the limits.…”

“…Several species have already been detected in emission for KELT-20 b at high resolution: Fe i (Yan et al 2022b;Borsa et al 2022), Si i (Cont et al 2021a, Fe ii, and Cr i (Borsa et al 2022). Fu et al ( 2022) also detected H 2 O and CO emission at low resolution.…”

“…We assumed a P-T profile of the form given by Eqn. 29 of Guillot (2010) as implemented in petitRADTRANS, with values of κ IR = 0.01 and γ = 5 chosen to approximate the P-T profiles retrieved for the dayside atmosphere of KELT-20 b by Yan et al (2022b), Fu et al (2022), andBorsa et al (2022). We show this profile in Fig.…”

“…In order to perform a final validation of our methodology and data, we attempt to reproduce the detections of emission from Fe i from Yan et al (2022b) and Borsa et al (2022), Si i from Cont et al (2021a), and Fe ii and Cr i from Borsa et al (2022). We estimated VMRs for these models using a FastChem (Stock et al 2018) equilibrium chemical model as implemented in PyFastChem 3 .…”

“…Here, we aim to detect or constrain which species may be responsible for this inversion. Yan et al (2022b) already obtained non-detections for TiO, VO, and FeH in their CARMENES data, while Borsa et al (2022) did the same for AlO, TiO, and VO with HARPS-N; however, both of those spectrographs are fed by 4-mclass telescopes, motivating an independent search with 8-m-class telescopes and including additional potential inversion agents.…”