The First Dynamical Mass Measurement in the HR 8799 System

Abstract

HR 8799 hosts four directly imaged giant planets, but none has a mass measured from first principles. We present the first dynamical mass measurement in this planetary system, finding that the innermost planet HR~8799~e has a mass of $9.6_{-1.8}^{+1.9}{M}_{\mathrm{Jup}}$. This mass results from combining the well-characterized orbits of all four planets with a new astrometric acceleration detection (5$\sigma$) from the Gaia EDR3 version of the Hipparcos-Gaia Catalog of Accelerations. We find with 95\% confidence that HR~8799~e is below $13M_{\mathrm{Jup}}$, the deuterium-fusing mass limit. We derive a hot-start cooling age of $42_{-16}^{+24}$\,Myr for HR~8799~e that agrees well with its hypothesized membership in the Columba association but is also consistent with an alternative suggested membership in the $\beta$~Pictoris moving group. We exclude the presence of any additional $\gtrsim$5-$M_{\mathrm{Jup}}$ planets interior to HR~8799~e with semi-major axes between $\approx$3-16\,au. We provide proper motion anomalies and a matrix equation to solve for the mass of any of the planets of HR~8799 using only mass ratios between the planets.

Accepted to ApJ Letters

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• Applying a temporal systematics model to vector Apodizing Phase Plate coronagraphic data: TRAP4vAPP
• PACOME: Optimal multi-epoch combination of direct imaging observations for joint exoplanet detection and orbit estimation
• A search for transits among the δ Scuti variables in Kepler
• The orbital architecture and stability of the $\mu$ Arae planetary system
• L-band Integral Field Spectroscopy of the HR 8799 Planetary System