* Astronomy

Title: A Second Giant Planet in 3:2 Mean-Motion Resonance in the HD 204313 System
Authors: Paul Robertson, J. Horner, Robert A. Wittenmyer, Michael Endl, William D. Cochran, Phillip J. MacQueen, Erik J. Brugamyer, Attila E. Simon, Stuart I. Barnes, Caroline Caldwell

We present 8 years of high-precision radial velocity (RV) data for HD 204313 from the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The star is known to have a giant planet (M sin i = 3.5 M_J) on a ~1900-day orbit, and a Neptune-mass planet at 0.2 AU. Using our own data in combination with the published CORALIE RVs of Segransan et al. (2010), we discover an outer Jovian (M sin i = 1.6 M_J) planet with P ~ 2800 days. Our orbital fit suggests the planets are in a 3:2 mean motion resonance, which would potentially affect their stability. We perform a detailed stability analysis, and verify the planets must be in resonance.

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