Orbital Properties of the HR 8799 Planetary System

We present a new dynamical analysis of the HR 8799 planetary system. This analysis takes advantage of improved astrometry from all data taken with the Keck II telescope by correcting for biases introduced by the NIRC2 camera's focal plane mask. We now have sufficient time coverage to constrain the orbital properties of these planets independent of stability considerations. We find that the planets cannot have high eccentricities (<0.4) and likely have similar inclinations, implying they formed in a common disk. Applying stability criteria to astrometrically-allowed orbits allows us to put constraints on the masses of these planets. The addition of a fourth planet makes it difficult, if not impossible, to find stable configurations for planetary masses greater than 7 Mjup. This argues that the lower masses predicted for a younger system age ( 30 Myr) are preferred. Using the lessons learned from this analysis, we perform simulations that show that we will be able to successfully constrain the eccentricity distribution of widely separated planets discovered by the upcoming Gemini Planet Imager Exoplanet Survey (GPIES). These constraints will be vital in determining the formation pathways for planets like those in the HR 8799 system.