The GAPS Programme at TNG

XXXIII. HARPS-N detects multiple atomic species in emission from the dayside of KELT-20b^★

¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
e-mail: francesco.borsa@inaf.it
² INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
³ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁴ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁶ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
⁷ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁸ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
¹⁰ INAF – Osservatorio Astronomico di Roma, via Frascati 33, I00040 Monte Porzio Catone (RM), Italy
¹¹ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹² Fundación Galileo Galilei - INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹³ Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, 38205 La Laguna, TF, Spain
¹⁴ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, TF, Spain
¹⁵ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁶ Department of Physics, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
¹⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁸ INAF – Osservatorio di Cagliari, via della Scienza 5, 09047 Selargius, CA, Italy
¹⁹ Dip. di Fisica e Astronomia Galileo Galilei – Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy

Received: 27 November 2021
Accepted: 10 April 2022

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 that show temperature inversions on their daysides by detecting metals emission lines in the dayside of KELT-20b. We first detected 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 performed a retrieval of the atmospheric temperature-pressure profile of the planet, confirming a thermal inversion. Then we created models of planetary emission of different species using the retrieved inverted temperature-pressure profile. By using the cross-correlation technique, we detected Fe I, Fe II, and Cr I at signal-to-noise ratio levels of 7.1, 3.9, and 3.6, respectively. The latter was detected in emission in the atmosphere of an exoplanet for the first time. Contrary to Fe I, Fe II and Cr I were detected only after the occultation and not before, hinting at different atmospheric properties in view during the pre- and post-occultation orbital phases. A further retrieval of the temperature-pressure profile performed independently during the pre- and post-occultation phases, while not highly significant, points to a steeper thermal inversion in the post-occultation.