The GAPS Programme at TNG

XXXVII. A precise density measurement of the young ultra-short period planet TOI-1807 b^★,★★

¹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
e-mail: domenico.nardiello@inaf.it
² Aix Marseille Univ, CNRS, CNES, LAM, 13000 Marseille, France
³ Dipartimento di Fisica e Astronomia “Galileo Galilei” – Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁵ INAF – Osservatorio Astrofísico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁶ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (Roma), Italy
⁷ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
⁸ INAF – Osservatorio Astrofísico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁹ Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
¹⁰ Dipartimento di Fisica – Università di Roma La Sapienza, P.le A. Moro 5, 00185 Roma, Italy
¹¹ Department of Physics and Astronomy, George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
¹² INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹³ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
¹⁴ Astronomy Department, Indiana University, Bloomington, IN 47405-7105, USA
¹⁵ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
¹⁶ Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
¹⁷ Max Planck Institute for Astronomy, Kõnigstuhl 17, 69117 Heidelberg, Germany
¹⁸ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
¹⁹ Fundación Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
²⁰ Instituto de Astrofísica de Canarias, C/Vía Lactea s/n, E-38205 La Laguna (Tenerife), Spain
²¹ Departamento de Astrofísica, Univ. de La Laguna, Av. del Astrofísico F. Sánchez, s/n, 38205 La Laguna (Tenerife), Spain

Received: 8 April 2022
Accepted: 1 June 2022

Abstract

Context. Great strides have been made in recent years in the understanding of the mechanisms involved in the formation and evolution of planetary systems. Despite this, many observational findings have not yet been corroborated by astrophysical explanations. A fine contribution to the study of planetary formation processes comes from the study of young, low-mass planets, with short orbital periods (<100 days). In the last three years, the NASA/TESS satellite has identified many planets of this kind and their characterization is clearly necessary in order to understand how they formed and evolved.

Aims. Within the framework of the Global Architecture of Planetary System (GAPS) project, we performed a validation and characterization (radius and mass) of the ultra-short period planet TOI-1807 b, which orbits its young host star BD+39 2643 (~300 Myr) in only 13 h. This is the youngest ultra-short period planet discovered so far.

Methods. Thanks to a joint modeling of the stellar activity and planetary signals in the TESS light curve and in new HARPS-N radial-velocity measurements, combined with accurate estimation of stellar parameters, we validated the planetary nature of TOI-1807 b and measured its orbital and physical parameters.

Results. By using astrometric, photometric, and spectroscopic observations, we found that BD+39 2643 is a young, active K dwarf star and a member of a 300 ± 80 Myr old moving group. Furthermore, it rotates in P_rot = 8.8 ± 0.1 days. This star hosts an ultra-short period planet, exhibiting an orbital period of only P_b = 0.54937 ± 0.00001 days. Thanks to the exquisite photometric and spectroscopic series, along with the accurate information on its stellar activity, we measured both the radius and the mass of TOI-1807 b with high precision, obtaining P_P,b = 1.37 ± 0.09 R_⊕ and M_P,b = 2.57 ± 0.50 M_⊕. These planet parameters correspond to a rocky planet with an Earth-like density (ρ_b = 1.0 ± 0.3 ρ_⊕) and no extended H/He envelope. From the analysis of the age-R_P distribution for planets with well measured ages, we inferred that TOI-1807 b may have already lost a large part of its atmosphere over the course of its 300 Myr lifetime.