The HARPS search for southern extra-solar planets. XXXIV. A planetary system around the nearby M dwarf GJ163, with a super-Earth possibly in the habitable zone
Abstract
The meter-per-second precision achieved by today velocimeters enables the search for 1-10 MEarth planets in the habitable zone of cool stars. This paper reports on the detection of 3 planets orbiting GJ163 (HIP19394), a M3 dwarf monitored by our ESO/HARPS search for planets. We made use of the HARPS spectrograph to collect 150 radial velocities of GJ163 over a period of 8 years. We searched the RV time series for coherent signals and found 5 distinct periodic variabilities. We investigated the stellar activity and casted doubts on the planetary interpretation for 2 signals. Before more data can be acquired we concluded that at least 3 planets are orbiting GJ163. They have orbital periods of Pb=8.632+-0.002, Pc=25.63+-0.03 and Pd=604+-8 days and minimum masses msini = 10.6+-0.6, 6.8+-0.9, and 29+-3 MEarth, respectively. We hold our interpretations for the 2 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. GJ163c, in particular, is a super-Earth with an equilibrium temperature of Teq = (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 (AEarth=0.2-0.3).