55 Cancri Revisited

The 55 Cancri Planetary System: Fully Self-Consistent N-body Constraints and a Dynamical Analysis

Authors:

Nelson

Abstract:

We present an updated study of the planets known to orbit 55 Cancri A using 1,418 high-precision radial velocity observations from four observatories (Lick, Keck, Hobby-Eberly Telescope, Harlan J. Smith Telescope) and transit time/durations for the inner-most planet, 55 Cancri "e" (Winn et al. 2011). We provide the first posterior sample for the masses and orbital parameters based on self-consistent n-body orbital solutions for the 55 Cancri planets, all of which are dynamically stable (for at least 108 years). We apply a GPU version of Radial velocity Using N-body Differential evolution Markov Chain Monte Carlo (RUN DMC; B. Nelson et al. 2014) to perform a Bayesian analysis of the radial velocity and transit observations. Each of the planets in this remarkable system has unique characteristics. Our investigation of high-cadence radial velocities and priors based on space-based photometry yields an updated mass estimate for planet "e" (7.99±0.25 M⊕), which affects its density (5.51±1.321.00 g cm−3) and inferred bulk composition. Dynamical stability dictates that the orbital plane of planet "e" must be aligned to within 60o of the orbital plane of the outer planets (which we assume to be coplanar). The mutual interactions between the planets "b" and "c" may develop an apsidal lock about 180o. We find 36-45% of all our model systems librate about the anti-aligned configuration with an amplitude of 51o±6o10o. Other cases showed short-term perturbations in the libration of ϖb−ϖc, circulation, and nodding, but we find the planets are not in a 3:1 mean-motion resonance. A revised orbital period and eccentricity for planet "d" pushes it further toward the closest known Jupiter analog in the exoplanet population.