Deep exploration of $\epsilon$ Eridani with Keck Ms-band vortex coronagraphy and radial velocities: mass and orbital parameters of the giant exoplanet

TL;DR

This study combines 30 years of radial velocity data and deep Ms-band imaging with vortex coronagraphy to precisely characterize the mass and orbit of the giant exoplanet $ ext{epsilon}$ Eridani b, confirming its presence and refining its parameters.

Contribution

It presents the first combined Bayesian analysis of RV and direct imaging data to constrain the properties of $ ext{epsilon}$ Eridani b, utilizing new high-sensitivity imaging and a comprehensive data set.

Findings

$ ext{epsilon}$ Eridani b has a mass of approximately 0.78 Jupiter masses.

The planet orbits at about 3.48 AU with a period of 7.37 years.

The orbit's eccentricity is very low, around 0.07, indicating a nearly circular orbit.

Abstract

We present the most sensitive direct imaging and radial velocity (RV) exploration of $\epsilon$ Eridani to date. $\epsilon$ Eridani is an adolescent planetary system, reminiscent of the early Solar system. It is surrounded by a prominent and complex debris disk which is likely stirred by one or several gas giant exoplanets. The discovery of the RV signature of a giant exoplanet was announced 15 years ago, but has met with scrutiny due to possible confusion with stellar noise. We confirm the planet with a new compilation and analysis of precise RV data spanning 30 years, and combine it with upper limits from our direct imaging search, the most sensitive ever performed. The deep images were taken in the Ms band (4.7$\mu$m) with the vortex coronagraph recently installed in W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive window for planet searches around nearby adolescent systems. The RV data and direct imaging upper limit maps were combined in an innovative joint Bayesian analysis, providing new constraints on the mass and orbital parameters of the elusive planet. $\epsilon$ Eridani b has a mass of $0.78^{+0.38}_{-0.12}$ $M_{Jup}$ and is orbiting $\epsilon$ Eridani at about $3.48\pm 0.02$ AU with a period of $7.37 \pm 0.07$ years. The eccentricity of $\epsilon$ Eridani b's orbit is $0.07^{+0.06}_{-0.05}$, an order of magnitude smaller than early estimates and consistent with a circular orbit. We discuss our findings from the standpoint of planet-disk interactions and prospects for future detection and characterization with the James Webb Space Telescope.