The HARPS search for southern extra-solar planets^{⋆,⋆⋆,⋆⋆⋆}

XXXIV. A planetary system around the nearby M dwarf GJ 163, with a super-Earth possibly in the habitable zone

¹ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
e-mail: xavier.Bonfils@obs.ujf-grenoble.fr
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ Department of Physics, I3N, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
⁴ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
⁵ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
⁶ Physikalisches Institut, Universitat Bern, Silderstrasse 5, 3012 Bern, Switzerland
⁷ Institut d’Astrophysique de Paris, CNRS, Université Pierre et Marie Curie, 98bis Bd. Arago, 75014 Paris, France
⁸ Laboratoire d’Astrophysique de Marseille, UMR 6110 CNRS, Université de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁹ Observatoire de Haute-Provence, 04870 Saint-Michel l’ Observatoire, France
¹⁰ Institut dAstrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium
¹¹ Astronomie et Systèmes Dynamiques, IMCCE-CNRS UMR 8028, Observatoire de Paris, UPMC, 77 Av. Denfert-Rochereau, 75014 Paris, France
¹² Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal

Received: 15 August 2012
Accepted: 4 June 2013

Abstract

The meter-per-second precision achieved by today’s velocimeters enables us to search for 1−10  M_⊕ planets in the habitable zone of cool stars. This paper reports on the detection of three planets orbiting GJ 163 (HIP 19394), a M3 dwarf monitored by our ESO/HARPS search for planets. We made use of the HARPS spectrograph to collect 150 radial velocities of GJ 163 over a period of eight years. We searched the radial-velocity time series for coherent signals and found five distinct periodic variabilities. We investigated the stellar activity and called into question the planetary interpretation for two signals. Before more data can be acquired we concluded that at least three planets are orbiting GJ 163. They have orbital periods of P_b = 8.632 ± 0.002, P_c = 25.63 ± 0.03, and P_d = 604 ± 8 days and minimum masses msini = 10.6 ± 0.6, 6.8 ± 0.9, and 29 ± 3  M_⊕, respectively. We hold our interpretations for the two additional signals with periods P_(e) = 19.4 and P_(f) = 108 days. The inner pair presents an orbital period ratio of 2.97, but a dynamical analysis of the system shows that it lays outside the 3:1 mean motion resonance. The planet GJ 163c, in particular, is a super-Earth with an equilibrium temperature of T_eq = (302 ± 10)(1 − A)^1/4 K and may lie in the so-called habitable zone for albedo values (A = 0.34 − 0.89) moderately higher than that of Earth (A_⊕ = 0.2−0.3).