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A precise architecture characterization of the π Mensae planetary system

M. Damasso, A. Sozzetti, C. Lovis, S. C. C. Barros, S. G. Sousa, O. Demangeon, J. P. Faria, J. Lillo Box, S. Cristiani, F. Pepe, R. Rebolo López, N. C. Santos, M. R. Zapatero-Osorio, J. I. González Hernández, M. Amate, L. Pasquini, F. M. Zerbi, V. Zh. Adibekyan, M. Abreu, M. Affolter, Y. Alibert, M. Aliverti, R. Allart, C. Allende Prieto, D. Álvarez Méndez, D. C. Alves, G. Avila, V. Baldini, T. Bandy, W. Benz, A. Bianco, F. Borsa, D. Bossini, V. Bourrier, F. Bouchy, C. Broeg, A. Cabral, G. Calderone, R. Cirami, J. Coelho, P. Conconi, I. Coretti, C. Cumani, G. Cupani, V. D'Odorico, S. Deiries, H. Dekker, B. Delabre, P. Di Marcantonio, X. Dumusque, D. Ehrenreich, P. Figueira, A. Fragoso, L. Genolet, M. Genoni, R. T. Génova-Santos, I. Hughes, O. Iwert, F. Kerber, J. Knudstrup, M. Landoni, B. Lavie, J.-L. Lizon, G. Lo Curto, C. Maire, C. J. A. P. Martins, D. Mégevand, A. Mehner, G. Micela, A. Modigliani, P. Molaro, M. A. Monteiro, M. J. P. F. G. Monteiro, M. Moschetti, E. Mueller, M. T. Murphy, N. J. Nunes, L. Oggioni, A. Oliveira, M. Oshagh, E. Pallé, G. Pariani, E. Poretti, J. L. Rasilla, J. M. Rebordão, E. Redaelli, M. Riva, S. Santana Tschudi, P. Santini, P. Santos, D. Ségransan, T. M. Schmidt, A. G. Segovia Milla, D. Sosnowska, P. Spanò, A. Suárez Mascareño, H. M. Tabernero, F. Tenegi, S. Udry, A. Zanutta

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 (ib =45.8−1.1+1.4 deg). This leads to the precise measurement of its absolute mass mb =14.1−0.4+0.5 MJup, 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.

Keywords
techniques: radial velocities; techniques: photometric; astrometry; planetary systems; stars: individual: π Men; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Solar and Stellar Astrophysics

Notes
Tables B.1 and B.2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A31

Based (in part) on Guaranteed Time Observations collected at the European Southern Observatory (ESO) under ESO programme(s) 1102.C-0744, 1102.C-0958, and 1104.C-0350 by the ESPRESSO Consortium.

Astronomy and Astrophysics
Volume 642, Article Number A31, Number of pages 14
2020 October

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia