A Second Giant Planet in 3:2 Mean-Motion Resonance in the HD 204313 System

TL;DR

This study reports the discovery of a second giant planet in the HD 204313 system, revealing a 3:2 mean-motion resonance that influences the system's stability, based on 8 years of high-precision radial velocity data.

Contribution

The paper presents the detection of a second giant planet in HD 204313 and confirms its resonant orbit through detailed stability analysis, which is a novel finding for this system.

Findings

Discovery of a second Jovian planet with ~2800-day period.

Confirmation of 3:2 mean-motion resonance between the planets.

Stability analysis supports the resonant orbital configuration.

Abstract

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.