The HARPS search for southern extra-solar planets XVII. Six long-period   giant planets around BD -17 0063, HD 20868, HD 73267, HD 131664, HD 145377,   HD 153950
  We report the discovery of six new substellar companions of main-sequence stars, detected through multiple Doppler measurements with the instrument HARPS installed on the ESO 3.6m telescope, La Silla, Chile. These extrasolar planets are orbiting the stars BD -17 0063, HD 20868, HD 73267, HD 131664, HD 145377, HD 153950. The orbital characteristics which best fit the observed data are depicted in this paper, as well as the stellar and planetary parameters. Masses of the companions range from 2 to 18 Jupiter masses, and periods range from 100 to 2000 days. The observational data are carefully analysed for activity-induced effects and we conclude on the reliability of the observed radial-velocity variations as of exoplanetary origin. Of particular interest is the very massive planet (or brown-dwarf companion) around the metal-rich HD 131664 with M2sini= 18.15 MJup, and a 5.34-year orbital period. These new discoveries reinforces the observed statistical properties of the exoplanet sample as known so far. 
C. Moutou, M. Mayor, G. Lo Curto, S. Udry, F. Bouchy, W. Benz, C.   Lovis, D. Naef, F. Pepe, D. Queloz, N.C. Santos