The Anglo-Australian planet search. XXV. A candidate massive Saturn analog orbiting HD 30177

Wittenmyer, Robert A. and Horner, Jonathan and Mengel, M. W. and Butler, R. P. and Wright, D. J. and Tinney, C. G. and Carter, B. D. and Jones, H. R. A. and Anglada-Escude, G. and Bailey, J. and O'Toole, Simon J. (2017) The Anglo-Australian planet search. XXV. A candidate massive Saturn analog orbiting HD 30177. The Astronomical Journal, 153 (4). pp. 1-12. ISSN 0004-6256

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We report the discovery of a second long-period giant planet orbiting HD 30177, a star previously known to host a massive Jupiter analog (HD 30177b: a=3.8$\pm$0.1 au, m sin $i=9.7\pm$0.5 Mjup). HD 30177c can be regarded as a massive Saturn analog in this system, with a=9.9$\pm$1.0 au and m sin $i=7.6\pm$3.1 Mjup. The formal best fit solution slightly favours a closer-in planet at $a\sim$7 au, but detailed n-body dynamical simulations show that configuration to be unstable. A shallow local minimum of longer-period, lower-eccentricity solutions was found to be dynamically stable, and hence we adopt the longer period in this work. The proposed $\sim$32 year orbit remains incomplete; further monitoring of this and other stars is necessary to reveal the population of distant gas giant planets with orbital separations $a\sim$10 au, analogous to that of Saturn.