The GAPS programme with HARPS-N@TNG IV: A planetary system around XO-2S

TL;DR

This study reports the discovery of a new planetary system around XO-2S, a wide binary companion to XO-2N, with two planets of different masses, demonstrating the system's stability and uniqueness in hosting planets.

Contribution

First confirmed case of a wide binary where both stars host planets, including a transiting planet, providing insights into planetary system diversity.

Findings

Detected a Jupiter-mass planet at 0.48 au with moderate eccentricity.

Identified a Saturn-mass planet at 0.13 au with moderate eccentricity.

System shows signs of a long-term radial velocity trend.

Abstract

We performed an intensive radial velocity monitoring of XO-2S, the wide companion of the transiting planet-host XO-2N, using HARPS-N at TNG in the framework of the GAPS programme. The radial velocity measurements indicate the presence of a new planetary system formed by a planet that is slightly more massive than Jupiter at 0.48 au and a Saturn-mass planet at 0.13 au. Both planetary orbits are moderately eccentric and were found to be dynamically stable. There are also indications of a long-term trend in the radial velocities. This is the first confirmed case of a wide binary whose components both host planets, one of which is transiting, which makes the XO-2 system a unique laboratory for understanding the diversity of planetary systems.