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 +/- 427 days, and a minimum mass of 5.3 M-Jup. HD 142c is thus a new Jupiter analog: a gas-giant planet with a long period and low eccentricity (e = 0.21 +/- 0.07). The second planet in the HD 159868 system has a period of 352.3 +/- 1.3 days and m sin i = 0.73 +/- 0.05 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.