Planetary system around LTT 1445A unveiled by ESPRESSO: Multiple planets in a triple M-dwarf system^★,★★

¹ Observatoire de l’Université de Genève, 51 chemin Pegasi, 1290 Sauverny, Switzerland
e-mail: baptiste.lavie@unige.ch
² Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
³ INAF – Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143, Trieste, Italy
⁴ INAF – Osservatorio Astrofísico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁵ Centro de Astrobiología (CSIC-INTA), Crta. Ajalvir km 4, 28850 Torrejon de Ardoz, Madrid, Spain
⁶ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁸ Instituto de Astrofísica e Ciencias do Espaco, Faculdade de Ciencias da Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016 Lisbon, Portugal
⁹ Departamento de Física e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal
¹⁰ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Region Metropolitana, Chile
¹¹ Instituto de Astrofísica e Ciencias do Espaco, CAUP, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹² Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151 Miramare, Trieste, Italy
¹³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748, Garching b. Munchen, Germany
¹⁴ Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹⁵ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
¹⁶ Consejo Superior de Investigaciones Cientícas, Spain
¹⁷ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁸ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal

Received: 25 December 2021
Accepted: 16 August 2022

Abstract

We present radial velocity follow-up obtained with ESPRESSO of the M-type star LTT 1445A (TOI-455), for which a transiting planet b with an orbital period of 5.4 days was detected by TESS. We report the discovery of a second transiting planet (LTT 1445A c) and a third non-transiting candidate planet (LTT 1445A d) with orbital periods of 3.12 and 24.30 days, respectively. The host star is the main component of a triple M-dwarf system at a distance of 6.9 pc. We used 84 ESPRESSO high-resolution spectra to determine accurate masses of 2.3 ± 0.3 M_⊕ and 1.0 ± 0.2 M_⊕ for planets b and c and a minimum mass of 2.7 ± 0.7 M_⊕ for planet d. Based on its radius of 1.43 ± 0.09 R_⊕ as derived from the TESS observations, LTT 1445A b has a lower density than the Earth and may therefore hold a sizeable atmosphere, which makes it a prime target for the James Webb Space Telescope (JWST). We used a Bayesian inference approach with the nested sampling algorithm and a set of models to test the robustness of the retrieved physical values of the system. There is a probability of 85% that the transit of planet c is grazing, which results in a retrieved radius with large uncertainties at 1.60_−0.34^+0.67 R_⊕. LTT 1445A d orbits the inner boundary of the habitable zone of its host star and could be a prime target for the JWST.