Secretly Eccentric: The Giant Planet and Activity Cycle of GJ 328

TL;DR

This paper reports the discovery of a massive, long-period exoplanet orbiting GJ 328, along with the identification of a stellar activity cycle that influences radial velocity measurements, refining the planet's orbital parameters.

Contribution

First detection of a ~2 Jupiter-mass planet with an eccentric 11-year orbit around GJ 328, including analysis of stellar activity effects on RV data.

Findings

Discovered a ~2 Jupiter-mass planet with an 11-year orbit.

Identified a stellar activity cycle affecting RV measurements.

Refined the planet's orbit to be more eccentric after correction.

Abstract

We announce the discovery of a ~2 Jupiter-mass planet in an eccentric 11-year orbit around the K7/M0 dwarf GJ 328. Our result is based on 10 years' worth of radial velocity (RV) data from the Hobby-Eberly and Harlan J. Smith telescopes at McDonald Observatory, and from the Keck Telescope at Mauna Kea. Our analysis of GJ 328's magnetic activity via the Na I D features reveals a long-period stellar activity cycle, which creates an additional signal in the star's RV curve with amplitude 6-10 m/s. After correcting for this stellar RV contribution, we see that the orbit of the planet is more eccentric than suggested by the raw RV data. GJ 328b is currently the most massive, longest-period planet discovered around a low-mass dwarf.