The orbital architecture and debris disks of the HR 8799 planetary system

TL;DR

This study models the orbital architecture of the HR 8799 system, revealing a stable resonant chain of planets and predicting potential undetected objects, while analyzing the debris disks' complex shapes through efficient dynamical simulations.

Contribution

Developed a CPU-efficient, self-consistent orbital model of HR 8799, confirming a resonant planetary chain and exploring debris disk structures influenced by planetary dynamics.

Findings

Planets likely in a Laplace resonance chain.

Predicted positions of undetected low-mass planets.

Revealed complex, possibly non-circular debris disk shapes.

Abstract

The HR8799 planetary system with four ~10 mJup planets in wide orbits up to 70 au, and periods up to 500 yr has been detected with the direct imaging. Its intriguing orbital architecture is not fully resolved due to time-limited astrometry covering ~20 years. Earlier, we constructed a heuristic model of the system based on rapid, convergent migration of the planets. We developed a better structured and CPU-efficient variant of this model. We re-analyzed the self-consistent, homogeneous astrometric dataset in Konopacky (2016). The best-fitting configuration agrees with our earlier findings. The planets are likely involved in dynamically robust Laplace resonance chain. Hypothetical planets with masses below the current detection limit of 0.1-3 Jupiter masses, within the observed inner, or beyond the outer orbit, respectively, do not influence the long term stability of the system. We predict positions of such non-detected objects. The long-term stable orbital model of the observed planets helps to simulate the dynamical structure of debris disks in the system. A CPU-efficient fast indicator technique makes it possible to reveal their complex, resonant shape in 10^6 particles scale. We examine the inner edge of the outer disk detected between 90-145 au. We also reconstruct the outer disk assuming that it has been influenced by convergent migration of the planets. A complex shape of the disk strongly depends on various dynamical factors, like orbits and masses of non-detected planets. It may be highly non-circular and its models are yet non-unique, regarding both observational constraints, as well as its origin.