GJ 328b: a VERY Eccentric 2 Jupiter Mass Exoplanet at 4.5 AU

SECRETLY ECCENTRIC: THE GIANT PLANET AND ACTIVITY CYCLE OF GJ 328

Authors:

1. Paul Robertson (a)

2. Michael Endl (a)

3. William D. Cochran (a)

4. Phillip J. MacQueen (a)

5. Alan P. Boss (b)

Affiliations:

a. Department of Astronomy and McDonald Observatory, University of Texas at Austin, Austin, TX 78712, USA

b. Department of Terrestrial Magnetism, Carnegie Institution, 5241 Broad Branch Road, NW, Washington DC 20015-1305, USA

Abstract:

We announce the discovery of a ~2 Jupiter-mass planet in an eccentric 11 yr orbit around the K7/M0 dwarf GJ 328. Our result is based on 10 years 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–1. 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.