An exact, generalised Laplace resonance in the HR 8799 planetary system

Abstract

A system of four super-Jupiter planets around HR 8799 is the first multi-planet configuration discovered via the direct imaging technique. Despite over decade of research, the system's architecture remains not fully resolved. The main difficulty comes from still narrow observing window of ~20 years that covers small arcs of orbits with periods from roughly 50 to 500 years. Soon after the discovery it became clear that unconstrained best-fitting astrometric configurations self-disrupt rapidly, due to strong mutual gravitational interactions between ~10-Jupiter-mass companions. Recently, we showed that the HR 8799 system may be long term stable when locked in a generalized Laplace 8:4:2:1 mean motion resonance (MMR) chain, and we constrained its orbits through the planetary migration. Here we qualitatively improve this approach by considering the MMR in terms of an exactly periodic configuration. This assumption enables us to construct for the first time the self-consistent $N$-body model of the long-term stable orbital architecture, using only available astrometric positions of the planets relative to the star. We independently determine planetary masses, which are consistent with thermodynamic evolution, and the parallax overlapping to $1\sigma$ with the most recent GAIA DR2 value. We also determine the global structure of the inner and outer debris discs in the [8, 600] au range, consistent with the updated orbital solution.

24 pages, 19 figures, 1 Table, the main paper with Appendix, accepted in Astrophysical Journal Letters

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• Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-Resolution Data
• Orbital and dynamical analysis of the system around HR 8799. New astrometric epochs from VLT/SPHERE and LBT/LUCI
• Keck/KPIC Emission Spectroscopy of WASP-33b
• Constraining planetesimal stirring: how sharp are debris disc edges?
• A Layered Debris Disk around M Star TWA 7 in Scattered Light
• Exomoons as sources of white dwarf pollution
• Resonant Chains of Exoplanets: Libration Centers for Three-body Angles
• Dynamical Mass of the Exoplanet Host Star HR 8799
• Deep orbital search for additional planets in the HR 8799 system
• MADYS: the Manifold Age Determination for Young Stars
• A gap-sharing planet pair shaping the crescent in HD 163296: a disk sculpted by a resonant chain
• Detectability of satellites around directly imaged exoplanets and brown dwarfs
• The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas
• The post-main-sequence fate of the HR 8799 planetary system
• Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes
• Periodic orbits in the 1:2:3 resonant chain and their impact on the orbital dynamics of the Kepler-51 planetary system
• Keplerian motion of a compact source orbiting the inner disc of PDS 70: a third protoplanet in resonance with b and c?
• Applying a temporal systematics model to vector Apodizing Phase Plate coronagraphic data: TRAP4vAPP
• On the origin of transition disk cavities: Pebble-accreting protoplanets vs Super-Jupiters
• PACOME: Optimal multi-epoch combination of direct imaging observations for joint exoplanet detection and orbit estimation
• Breaking long-period resonance chains with stellar flybys
• Resonant chains in triple-planetary systems
• Architecture of planetary systems predicted from protoplanetary disks observed with ALMA II: evolution outcomes and dynamical stability
• Stability of a cluster-disrupted mean-motion resonance (chain) in HR 8799 and PDS 70