Letter to the Editor

TESS’s first planet

A super-Earth transiting the naked-eye star π Mensae^⋆

¹ Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino, Italy
e-mail davide.gandolfi@unito.it
² Department of Astronomy, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁴ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ Stellar Astrophysics Centre, Deparment of Physics and Astronomy, Aarhus University, Ny Munkegrade 120, 8000 Aarhus C, Denmark
⁶ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
⁷ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8041 Graz, Austria
⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206 Tenerife, Spain
⁹ Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁰ Rheinisches Institut für Umweltforschung, Abteilung Planetenforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
¹¹ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
¹² IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
¹³ Université Paris Diderot, AIM, Sorbonne Paris Cité, CEA, CNRS, 91191 Gif-sur-Yvette, France
¹⁴ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
¹⁵ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenberg, Germany
¹⁶ Department of Astronomy and McDonald Observatory, University of Texas at Austin, 2515 Speedway, Stop C1400 Austin, TX 78712, USA

Received: 20 September 2018
Accepted: 28 September 2018

Abstract

We report on the confirmation and mass determination of π Men c, the first transiting planet discovered by NASA’s TESS space mission. π Men is a naked-eye (V = 5.65 mag), quiet G0 V star that was previously known to host a sub-stellar companion (π Men b) on a longperiod (P_orb = 2091 days), eccentric (e = 0.64) orbit. Using TESS time-series photometry, combined with Gaia data, published UCLES at AAT Doppler measurements, and archival HARPS at ESO-3.6m radial velocities, we found that π Men c is a close-in planet with an orbital period of P_orb = 6.27 days, a mass of M_c = 4.52 ± 0.81 M_⊕, and a radius of R_c = 2.06 ± 0.03 R_⊕. Based on the planet’s orbital period and size, π Men c is a super-Earth located at, or close to, the radius gap, while its mass and bulk density suggest it may have held on to a significant atmosphere. Because of the brightness of the host star, this system is highly suitable for a wide range of further studies to characterize the planetary atmosphere and dynamical properties. We also performed an asteroseismic analysis of the TESS data and detected a hint of power excess consistent with the seismic values expected for this star, although this result depends on the photometric aperture used to extract the light curve. This marginal detection is expected from pre-launch simulations hinting at the asteroseismic potential of the TESS mission for longer, multi-sector observations and/or for more evolved bright stars.