The Anglo-Australian Planet Search. XXII. Two New Multi-Planet Systems

TL;DR

This paper reports the discovery of two new multi-planet systems around stars HD 142 and HD 159868, highlighting how additional planets can influence perceived orbital eccentricities in exoplanet systems.

Contribution

It presents the detection of two new planets in previously known systems, demonstrating the importance of considering multiple planets in orbital analysis.

Findings

HD 142c is a Jupiter analog with a long orbital period.

The second planet in HD 159868 has a period of about one year.

Including additional planets reduces the eccentricity of previously known planets.

Abstract

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.