A precise architecture characterization of theπMensae planetary system

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.

The TESS Objects of Interest Catalog from the TESS Prime Mission

“…The system was observed in multiple sectors in TESS year 1. Additional observations and analysis have provided more precise mass measurement for planets b and c, their large orbit misalignment, and possible theories for the formation of the system (Kane et al 2020;Xuan & Wyatt 2020;Damasso et al 2020;De Rosa et al 2020;Kunovac Hodžić et al 2021). Although π Men is a bright star, it is a viable candidate for JWST observation.…”

A significant mutual inclination between the planets within the π Mensae system

“…While this manuscript was being reviewed independent analyses of the same astrometric datasets by Xuan & Wyatt (2020); Damasso et al (2020) were published. We derive consistent results on the mutual inclination of the two planets despite using a different approach for incorporating the various astrometric measurements of the system.…”

A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c

“…While ohmic heating may occur at sub-Neptunes (Pu & Valencia 2017), the predicted amount falls short by two orders of magnitude of what is needed for π Men c (Figure 8, top right). Another option is tidal heating, provided that the planet is on an eccentric orbit, although the orbital eccentricity remains poorly constrained (Gandolfi et al 2018;Huang et al 2018;Damasso et al 2020). For an eccentricity e = 0.001 and tidal quality factor Q p 10 3 , we find that tidal heating affects negligibly the planetary cooling.…”

“…Assuming that water is the dominant heavy volatile, it is plausible that π Men c might have formed beyond the snow line and reached its current orbit following high-eccentricity migration and tidal circularization. The idea is supported by π Men c being on a misaligned orbit with respect to the stellar spin axis (Kunovac Hodžić et al 2020) and the fact that the system contains a far-out gas giant on an eccentric, inclined orbit (Damasso et al 2020;De Rosa et al 2020;Xuan & Wyatt 2020).…”