A Radial Velocity Study of the Planetary System of Pi Mensae: Improved Planet Parameters for PI Mensae c and a Third Planet on a 125-d Orbit

Abstract

Pi Men hosts a transiting planet detected by the TESS space mission and an outer planet in a 5.7-yr orbit discovered by RV surveys. We studied this system using new radial velocity (RV) measurements taken with the HARPS spectrograph on ESO's 3.6-m telescope as well as archival data. We constrain the stellar RV semi-amplitude due to the transiting planet, Pi Men c, as K_c = 1.21 +/- 0.12 m/s resulting in a planet mass of M_c = 3.63 +/- 0.38 M_Earth. A planet radius of R_c= 2.145 +/- 0.015 R_Earth yields a bulk density of rho = 2.03 +/- 0.22 g/cm^{-3}. The precisely determined density of this planet and the brightness of the host star make Pi Men c an excellent laboratory for internal structure and atmospheric characterization studies. Our HARPS RV measurements also reveal compelling evidence for a third body, PI Men d, with a minimum mass M sin i = 13.38 +/- 1.35 M_Earth orbiting with a period of P_d = 125 d on an eccentric orbit (e = 0.22). A simple dynamical analysis indicates that the orbit of Pi Men d is stable on timescales of at least 20 Myrs. Given the mutual inclination between the outer gaseous giant and the inner rocky planet and the presence of a third body at 125 d, Pi Men is an important planetary system for dynamical and formation studies.

arXiv commentAccepted for publication in the Astronomical Journal. 40 pages, 16 figures

References in corpus (38)

• Gaia Data Release 2. Summary of the contents and survey properties
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• The PLATO 2.0 Mission
• REBOUND: An open-source multi-purpose N-body code for collisional dynamics
• Catalog of Nearby Exoplanets
• The evaporation valley in the Kepler planets
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• Core-powered mass loss and the radius distribution of small exoplanets
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• Mass-Radius Relation for Rocky Planets based on PREM
• Sculpting the Valley in the Radius Distribution of Small Exoplanets as a by-product of Planet Formation: The Core-Powered Mass-Loss Mechanism
• The HARPS-TERRA project I. Description of the algorithms, performance and new measurements on a few remarkable stars observed by HARPS
• A new list of thorium and argon spectral lines in the visible
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• Evidence for a Long-period Planet Orbiting Epsilon Eridani
• TESS Discovery of a Transiting Super-Earth in the $\pi$ Mensae System
• The CARMENES search for exoplanets around M dwarfs. First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems
• TESS's first planet: a super-Earth transiting the naked-eye star $\pi$ Mensae
• An Investigation into the Radial Velocity Variations of CoRoT-7
• Stacked Bayesian general Lomb-Scargle periodogram: Identifying stellar activity signals
• Pyaneti: a fast and powerful software suite for multi-planet radial velocity and transit fitting
• Evidence for a high mutual inclination between the cold Jupiter and transiting super Earth orbiting $\pi$ Men
• Further evidence for the planet around 51 Pegasi
• A probable planetary companion to HD 39091 from the Anglo-Australian Planet Search
• Deep exploration of $\epsilon$ Eridani with Keck Ms-band vortex coronagraphy and radial velocities: mass and orbital parameters of the giant exoplanet
• A 20-Second Cadence View of Solar-Type Stars and Their Planets with TESS: Asteroseismology of Solar Analogs and a Re-characterization of pi Men c
• A precise architecture characterization of the $\pi$ Men planetary system
• Kepler-108: A Mutually Inclined Giant Planet System
• A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c
• Is pi Men c's atmosphere hydrogen-dominated? Insights from a non-detecton of Hy Ly-alpha absorption
• Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity
• Mass determinations of the three mini-Neptunes transiting TOI-125
• A significant mutual inclination between the planets within the $\pi$ Mensae system
• Precise radial velocities of giant stars. XII. Evidence against the proposed planet Aldebaran b
• Periodic Halpha variations in GL 581: Further evidence for an activity origin to GL 581d

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• Prospects from TESS and Gaia to constrain the flatness of planetary systems
• Luminaries in the Sky: The TESS Legacy Sample of Bright Stars. I. Asteroseismic detections in naked-eye main-sequence and sub-giant solar-like oscillators
• Dynamical Architectures of S-type Transiting Planets in Binaries I: Target Selection using Hipparcos and Gaia proper motion anomalies
• TOI-733 b: a planet in the small-planet radius valley orbiting a Sun-like star
• True Masses using RV data with Hipparcos and Gaia Astrometry
• SPORES-HWO. II. Companion Mass Limits and Updated Planet Properties for 120 Future Exoplanet Imaging Targets from 35 yr of Precise Doppler Monitoring