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Description
The bright star {pi} 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 ESO's Very-Large Telescope (VLT). The star hosts a multi-planet system (a transiting 4M_{earth}_ planet at ~0.07au, and a sub-stellar companion on a ~2100-day eccentric orbit) which is particularly appealing for a precise multi-technique characterization. With the new ESPRESSO observations, that cover a time span of 200days, we aim to improve the precision and accuracy of the planet parameters and search for additional low-mass companions. We also take advantage of new photometric transits of {pi} Men c observed by TESS over a time span that overlaps with that of the ESPRESSO follow-up campaign. We analyse the enlarged spectroscopic and photometric datasets and compare the results to those in the literature. We further characterize 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. We present a precise characterization of the planetary system around {pi} Men. The ESPRESSO radial velocities alone (37 nightly binned data with typical uncertainty of 10cm/s) allow for a precise retrieval of the Doppler signal induced by {pi} Men c. The residuals show an RMS of 1.2m/s, which is half that of the HARPS data and, based on them, we put limits on the presence of additional low-mass planets (e.g. we can exclude companions with a minimum mass less than ~2M_{earth}_ within the orbit of {pi} Men c). We improve the ephemeris of {pi} Men c using 18 additional TESS transits, and in combination with the astrometric measurements, we determine the inclination of the orbital plane of {pi} Men b with high precision (i_b_=45.8^+1.4^_-1.1_deg). This leads to the precise measurement of its absolute mass m_b_=14.1^+0.5^_-0.4_Mjup, indicating that {pi} Men b can be classified as a brown dwarf. {pi} Men represents a nice example of the extreme precision radial velocities that can be obtained with ESPRESSO for bright targets. Our determination of the 3-D architecture of the {pi} Men planetary system, and the high relative misalignment of the planetary orbital planes, put constraints and challenges to the theories of formation and dynamical evolution of planetary systems. The accurate measurement of the mass of {pi} Men b contributes to make the brown dwarf desert a bit greener.
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