[hal-00462209] The HARPS search for southern extra-solar planets. XIX. Characterization and dynamics of the GJ 876 planetary system

Precise radial-velocity measurements for data acquired with the HARPS spectrograph infer that three planets orbit the M 4 dwarf star GJ 876. In particular, we confirm the existence of planet d, which orbits every 1.93785 days. We find that its orbit may have significant eccentricity (e = 0.14), and deduce a more accurate estimate of its minimum mass of 6.3~M_⊕. Dynamical modeling of the HARPS measurements combined with literature velocities from the Keck Observatory strongly constrain the orbital inclinations of the b and c planets. We find that ib = 48.9° ± 1.0° and ic = 48.1° ± 2.1°, which infers the true planet masses of Mb = 2.64~± 0.04~M_Jup and Mc = 0.83 ± 0.03~M_Jup, respectively. Radial velocities alone, in this favorable case, can therefore fully determine the orbital architecture of a multi-planet system, without the input from astrometry or transits. The orbits of the two giant planets are nearly coplanar, and their 2:1 mean motion resonance ensures stability over at least 5 Gyr. The libration amplitude is smaller than 2°, suggesting that it was damped by some dissipative process during planet formation. The system has space for a stable fourth planet in a 4:1 mean motion resonance with planet b, with a period around 15 days. The radial velocity measurements constrain the mass of this possible additional planet to be at most that of the Earth. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory under the GTO programme ID 072.C-0488; and on observations obtained at the Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology.The Table with the HARPS radial velocities is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://ift.tt/1Auo8xb



from HAL : Dernières publications http://ift.tt/1pxeyHF