Publication Date:
2014-04-27
Description:
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 10 8 yr). We apply a GPU version of Radial velocity Using N -body Differential evolution Markov Chain Monte Carlo ( run dmc ; Nelson, Ford & Payne) 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’ (8.09 ± 0.26 M ), which affects its density ( $5.51\pm ^{1.32}_{1.00}$ g cm –3 ) and inferred bulk composition. Dynamical stability dictates that the orbital plane of planet ‘e’ must be aligned to within 60° 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 180°. We find 36–45 per cent of all our model systems librate about the anti-aligned configuration with an amplitude of $51^\circ \pm ^{6^\circ }_{10^\circ }$ . Other cases showed short-term perturbations in the libration of b – c , 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 towards the closest known Jupiter analogue in the exoplanet population.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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