The Lick-Carnegie Exoplanet Survey: Gliese 687b: A Neptune-Mass Planet Orbiting a Nearby Red Dwarf

TL;DR

This paper reports the discovery of a Neptune-mass exoplanet orbiting a nearby red dwarf star using precision radial velocity measurements, demonstrating the effectiveness of the Automated Planet Finder in detecting low-mass planets around low-mass stars.

Contribution

First detection of a Neptune-mass planet around a nearby M dwarf using the APF telescope, highlighting its capability for low-mass planet surveys.

Findings

Discovered an 18 Earth-mass planet with a 38-day orbit.

Confirmed the planet's Keplerian origin despite stellar activity.

Demonstrated APF's suitability for low-mass planet detection.

Abstract

Precision radial velocities from the Automated Planet Finder and Keck/HIRES reveal an M*sin(i) =18 +/- 2 Earth mass planet orbiting the nearby M3V star GJ 687. This planet has an orbital period, P = 38.14 days, and a low orbital eccentricity. Our Stromgren b and y photometry of the host star suggests a stellar rotation signature with a period of P = 60 days. The star is somewhat chromospherically active, with a spot filling factor estimated to be several percent. The rotationally{induced 60-day signal, however, is well-separated from the period of the radial velocity variations, instilling confidence in the interpretation of a Keplerian origin for the observed velocity variations. Although GJ 687b produces relatively little specific interest in connection with its individual properties, a compelling case can be argued that it is worthy of remark as an eminently typical, yet at a distance of 4.52 pc, a very nearby representative of the galactic planetary census. The detection of GJ 687b indicates that the APF telescope is well suited to the discovery of low-mass planets orbiting low-mass stars in the as-yet relatively un-surveyed region of the sky near the north celestial pole.