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A Radial Velocity Study of the Planetary System of π Mensae: Improved Planet Parameters for π Mensae c and a Third Planet on a 125 Day Orbit

Hatzes, Artie P.; Gandolfi, Davide; Korth, Judith; Rodler, Florian; Sabotta, Silvia; Esposito, Massimiliano; Barragán, Oscar; Van Eylen, Vincent; Livingston, John H.; Serrano, Luisa Maria; Luque, Rafael; Smith, Alexis M. S.; Redfield, Seth; Persson, Carina M.; Pätzold, Martin; Palle, Enric; Nowak, Grzegorz; Osborne, Hannah L. M.; Narita, Norio; Mathur, Savita; Lam, Kristine W. F.; Kabáth, Petr; Johnson, Marshall C.; Guenther, Eike W.; Grziwa, Sascha; Goffo, Elisa; Fridlund, Malcolm; Endl, Michael; Deeg, Hans J.; Csizmadia, Szilard; Cochran, William D.; Cuesta, Lucía González; Chaturvedi, Priyanka; Carleo, Ilaria; Cabrera, Juan; Beck, Paul G.; Albrecht, Simon

Zentrum für Astronomie und Astrophysik

π Men hosts a transiting planet detected by the Transiting Exoplanet Survey Satellite space mission and an outer planet in a 5.7 yr orbit discovered by radial velocity (RV) surveys. We studied this system using new RV measurements taken with the HARPS spectrograph on ESO’s 3.6 m telescope, as well as archival data. We constrain the stellar RV semiamplitude due to the transiting planet, π Men c, as Kc = 1.21 ± 0.12 m s−1, resulting in a planet mass of Mc = 3.63 ± 0.38 M⊕. A planet radius of Rc = 2.145 ± 0.015 R⊕ yields a bulk density of ρc = 2.03 ± 0.22 g cm−3. The precisely determined density of this planet and the brightness of the host star make π Men c an excellent laboratory for internal structure and atmospheric characterization studies. Our HARPS RV measurements also reveal compelling evidence for a third body, π Men d, with a minimum mass Md sin id = 13.38 ± 1.35 M⊕ orbiting with a period of Porb,d = 125 days on an eccentric orbit (ed = 0.22). A simple dynamical analysis indicates that the orbit of π Men d is stable on timescales of at least 20 Myr. Given the mutual inclination between the outer gaseous giant and the inner rocky planet and the presence of a third body at 125 days, π Men is an important planetary system for dynamical and formation studies.