The California Planet Survey III. A Possible 2:1 Resonance in the Exoplanetary Triple System HD 37124

TL;DR

This paper refines the orbital parameters of the HD 37124 exoplanet system, identifies a possible 2:1 resonance between two planets, and discusses the significance of period commensurabilities in multi-planet systems.

Contribution

It provides improved orbital solutions for HD 37124, resolves previous ambiguities, and analyzes the prevalence of period commensurabilities in exoplanet systems.

Findings

Outer two planets have an apparent 2:1 period ratio.

Resonant and non-resonant configurations are consistent with data.

About one-third of well-characterized multi-planet systems show low-order period commensurabilities.

Abstract

We present new radial velocities from Keck Observatory and both Newtonian and Keplerian solutions for the triple-planet system orbiting HD 37124. The orbital solution for this system has improved dramatically since the third planet was first reported in Vogt et al. 2005 with an ambiguous orbital period. We have resolved this ambiguity, and the outer two planets have an apparent period commensurability of 2:1. A dynamical analysis finds both resonant and non-resonant configurations consistent with the radial velocity data, and constrains the mutual inclinations of the planets to be less than about 30 degrees. We discuss HD 37124 in the context of the other 19 exoplanetary systems with apparent period commenserabilities, which we summarize in a table. We show that roughly one in three well-characterized multiplanet systems has a apparent low-order period commensuribility, which is more than would naively be expected if the periods of exoplanets in known multiplanet systems were drawn randomly from the observed distribution of planetary orbital periods.