A precise architecture characterization of theπMensae planetary system

Abstract

Context.The bright starπMen 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 4M⊕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 ofπMen 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 HIPPARCOSandGaia. 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 aroundπMen. 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 byπMen 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 ~2M⊕within the orbit ofπMen c). We improve the ephemeris ofπMen c using 18 additional TESS transits, and, in combination with the astrometric measurements, we determine the inclination of the orbital plane ofπMen b with high precision (ib=45.8−1.1+1.4deg). This leads to the precise measurement of its absolute massmb=14.1−0.4+0.5MJup, indicating thatπMen b can be classified as a brown dwarf.Conclusions.TheπMen 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 theπMen 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 ofπMen b contributes to make the brown dwarf desert a bit greener.