A precise architecture characterization of the π Mensae planetary system^★,★★

¹ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
e-mail: mario.damasso@inaf.it
² Département d’astronomie, Université de Genève, 51 ch. des Maillettes, 1290 Versoix, Switzerland
³ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁴ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁵ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁶ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
⁷ Institute for Fundamental Physics of the Universe, IFPU, Via Beirut 2, 34151 Grignano, Trieste, Italy
⁸ Instituto de Astrofisica de Canarias, Via Lactea, 38200 La Laguna, Tenerife, Spain
⁹ Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁰ Consejo Superior de Investigaciones Científicas, 28006 Madrid, Spain
¹¹ ESO, European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
¹² INAF – Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy
¹³ Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal
¹⁴ Departamento de Física da Faculdade de Ciências da Univeridade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal
¹⁵ Physics Institute of University of Bern, Gesellschaftsstrasse, 6, 3012 Bern, Switzerland
¹⁶ ESO, European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago
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
¹⁹ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
²⁰ NRCC-HIA, 5071 West Saanich Road Building VIC-10, Victoria, British Columbia V9E 2E, Canada

Received: 14 May 2020
Accepted: 9 July 2020

Abstract

Context. The bright star π Men was chosen as the first target for a radial velocity follow-up to test the performance of ESPRESSO, the new high-resolution spectrograph at the European Southern Observatory’s Very Large Telescope. The star hosts a multi-planet system (a transiting 4 M_⊕ planet at ~0.07 au and a sub-stellar companion on a ~2100-day eccentric orbit), which is particularly suitable for a precise multi-technique characterization.

Aims. With the new ESPRESSO observations, which cover a time span of 200 days, we aim to improve the precision and accuracy of the planet parameters and search for additional low-mass companions. We also take advantage of the new photometric transits of π Men c observed by TESS over a time span that overlaps with that of the ESPRESSO follow-up campaign.

Methods. We analysed the enlarged spectroscopic and photometric datasets and compared the results to those in the literature. We further characterized the system by means of absolute astrometry with HIPPARCOS and Gaia. We used the high-resolution spectra of ESPRESSO for an independent determination of the stellar fundamental parameters.

Results. We present a precise characterization of the planetary system around π Men. The ESPRESSO radial velocities alone (37 nightly binned data with typical uncertainty of 10 cm s⁻¹) allow for a precise retrieval of the Doppler signal induced by π Men c. The residuals show a root mean square of 1.2 m s⁻¹, which is half that of the HARPS data; based on the residuals, we put limits on the presence of additional low-mass planets (e.g. we can exclude companions with a minimum mass less than ~2 M_⊕ within the orbit of π Men c). We improve the ephemeris of π Men c using 18 additional TESS transits, and, in combination with the astrometric measurements, we determine the inclination of the orbital plane of π Men b with high precision (i_b =45.8_−1.1^+1.4 deg). This leads to the precise measurement of its absolute mass m_b =14.1_−0.4^+0.5 M_Jup, indicating that π Men b can be classified as a brown dwarf.

Conclusions. The π Men system represents a nice example of the extreme precision radial velocities that can be obtained with ESPRESSO for bright targets. Our determination of the 3D architecture of the π Men planetary system and the high relative misalignment of the planetary orbital planes put constraints on and challenge the theories of the formation and dynamical evolution of planetary systems. The accurate measurement of the mass of π Men b contributes to make the brown dwarf desert a bit greener.