The Anglo-Australian Planet Search. XXII. Two New Multi-Planet Systems
  We report the detection of two new planets from the Anglo-Australian Planet Search. These planets orbit two stars each previously known to host one planet. The new planet orbiting HD 142 has a period of 6005\pm427 days, and a minimum mass of 5.3M_Jup. HD142c is thus a new Jupiter analog: a gas-giant planet with a long period and low eccentricity (e = 0.21 \pm 0.07). The second planet in the HD 159868 system has a period of 352.3\pm1.3 days, and m sin i=0.73\pm0.05 M_Jup. In both of these systems, including the additional planets in the fitting process significantly reduced the eccentricity of the original planet. These systems are thus examples of how multiple-planet systems can masquerade as moderately eccentric single-planet systems. 
Robert A. Wittenmyer, J. Horner, M. Tuomi, G. S. Salter, C. G. Tinney,   R. P. Butler, H. R. A. Jones, S. J. O'Toole, J. Bai...
astro-ph.EP