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 M4 dwarf star GJ876. 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 MJup and Mc = 0.83 ± 0.03 MJup, 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.

[1]  A. Wolszczan,et al.  Masses and Orbital Inclinations of Planets in the PSR B1257+12 System , 2003, astro-ph/0305536.

[2]  D. Queloz,et al.  The HARPS search for southern extra-solar planets. X. A m sin i = 11 M_â planet around the nearby spotted M dwarf GJ 674 , 2007, 0704.0270.

[3]  A. Crida,et al.  Influence of an inner disc on the orbital evolution of massive planets migrating in resonance , 2008, 0802.2014.

[4]  Extrasolar Planets in Mean-Motion Resonance: Apses Alignment and Asymmetric Stationary Solutions , 2002, astro-ph/0210577.

[5]  N. Santos,et al.  Metallicity of M dwarfs , 2005 .

[6]  D. Queloz,et al.  The HARPS search for southern extra-solar planets. XI. Super-Earths (5 and 8 M{⊕}) in a 3-planet system , 2007, 0704.3841.

[7]  P. H. Hauschildt,et al.  Infrared Spectra and Spectral Energy Distributions of Late M and L Dwarfs , 2000, astro-ph/0010174.

[8]  A. Correia SECULAR EVOLUTION OF A SATELLITE BY TIDAL EFFECT: APPLICATION TO TRITON , 2009, 0909.4210.

[9]  D. Frail,et al.  A planetary system around the millisecond pulsar PSR1257 + 12 , 1992, Nature.

[10]  Jacques Laskar,et al.  Frequency analysis for multi-dimensional systems: global dynamics and diffusion , 1993 .

[11]  D. Queloz,et al.  The HARPS search for southern extra-solar planets - VI. A Neptune-mass planet around the nearby M dwarf Gl 581 , 2005 .

[12]  Wm. A. Wheaton,et al.  2MASS All Sky Catalog of point sources. , 2003 .

[13]  J. Laskar,et al.  HD60532, a planetary system in a 3:1 mean motion resonance , 2009, 0902.0667.

[14]  N. Santos,et al.  Metallicity of M dwarfs - I. A photometric calibration and the impact on the mass-luminosity relation at the bottom of the main sequence , 2005, astro-ph/0503260.

[15]  W. Press,et al.  Numerical Recipes in Fortran: The Art of Scientific Computing.@@@Numerical Recipes in C: The Art of Scientific Computing. , 1994 .

[16]  The low-level radial velocity variability in Barnard's star (= GJ 699) ? Secular acceleration, indications for convective redshift, and planet mass limits , 2003, astro-ph/0303528.

[17]  R. Mardling,et al.  Long-term tidal evolution of short-period planets with companions , 2007, 0706.0224.

[18]  P. Goldreich Inclination of satellite orbits about an oblate precessing planet , 1965 .

[19]  William H. Press,et al.  Numerical recipes in FORTRAN (2nd ed.): the art of scientific computing , 1992 .

[20]  S. Leggett Infrared Colors of Low-Mass Stars , 1992 .

[21]  Michel Mayor,et al.  The HARPS search for southern extra-solar planets - XVI. HD 45364, a pair of planets in a 3:2 mean motion resonance , 2009 .

[22]  M. López-Morales,et al.  HOW ECCENTRIC ORBITAL SOLUTIONS CAN HIDE PLANETARY SYSTEMS IN 2:1 RESONANT ORBITS , 2008, 0809.1275.

[23]  J. Bean,et al.  The architecture of the GJ 876 planetary system - Masses and orbital coplanarity for planets b and c , 2009, 0901.3144.

[24]  Dynamics and Origin of the 2:1 Orbital Resonances of the GJ 876 Planets , 2001, astro-ph/0108104.

[25]  J. Lissauer,et al.  A ~7.5 M⊕ Planet Orbiting the Nearby Star, GJ 876* , 2005, astro-ph/0510508.

[26]  Evolution of the obliquities of the giant planets in encounters during migration , 2006, astro-ph/0612330.

[27]  F. Bouchy,et al.  The HARPS search for southern extra-solar planets - XVII. Super-Earth and Neptune-mass planets in multiple planet systems HD 47 186 and HD 181 433 , 2008, 0812.1608.

[28]  J. Lissauer,et al.  Dynamical Models of the Resonant Pair of Planets Orbiting the Star GJ 876 , 2001 .

[29]  J. Lissauer,et al.  Resonant Inclination Excitation of Migrating Giant Planets , 2003, astro-ph/0308112.

[30]  R. Paul Butler,et al.  A Pair of Resonant Planets Orbiting GJ 876 , 2001 .

[31]  J. Laskar,et al.  The CORALIE survey for southern extra-solar planets - XIII. A pair of planets around HD 202206 or a circumbinary planet? , 2005 .

[32]  F. Bouchy,et al.  The HARPS search for southern extra-solar planets: XVIII. An Earth-mass planet in the GJ 581 planetary system , 2009, 0906.2780.

[33]  Todd J. Henry,et al.  The mass-luminosity relation for stars of mass 1.0 to 0.08 solar mass , 1993 .

[34]  Jacques Laskar,et al.  The chaotic motion of the solar system: A numerical estimate of the size of the chaotic zones , 1990 .

[35]  J. Laskar,et al.  High order symplectic integrators for perturbed Hamiltonian systems , 2000 .

[36]  Averaging on the motion of a fast revolving body. Application to the stability study of a planetary system , 2009 .

[37]  A Planetary Companion to a Nearby M4 Dwarf, Gliese 876* , 1998, astro-ph/9807307.

[38]  S. Hawley,et al.  The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity , 1996 .

[39]  X. Delfosse,et al.  A Mass for the Extrasolar Planet Gliese 876b Determined from Hubble Space Telescope Fine Guidance Sensor 3 Astrometry and High-Precision Radial Velocities , 2002, astro-ph/0212101.

[40]  D. Queloz,et al.  The HARPS search for southern extra-solar planets - XIV. Gl 176b, a super-Earth rather than a Neptune, and at a different period , 2008, 0809.0750.

[41]  Guangyu Li,et al.  The Dynamical Simulations of the Planets Orbiting GJ 876 , 2002 .

[42]  S. Ida,et al.  Orbital Evolution of Asteroids during Depletion of the Solar Nebula , 2000 .

[43]  K. Tsiganis,et al.  Kozai resonance in extrasolar systems , 2009 .

[44]  Jean-Luis Lizon,et al.  Setting New Standards with HARPS , 2003 .

[45]  Yi-sui Sun,et al.  The Effect of Sweeping Secular Resonances on the Classical Kuiper Belt , 2008 .

[46]  K. Apps,et al.  ON THE METAL RICHNESS OF M DWARFS WITH PLANETS , 2009, 0904.3092.