Papers › The First Dynamical Mass Measurement in the HR 8799 System
The First Dynamical Mass Measurement in the HR 8799 System
G. Mirek Brandt, Timothy D. Brandt, Trent J. Dupuy, Daniel Michalik, Gabriel-Dominique Marleau
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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^(+1.9)_(-1.8) M_(Jup). This mass results from combining the well-characterized orbits of all four planets with a new astrometric acceleration detection (5σ) from the Gaia EDR3 version of the Hipparcos-Gaia Catalog of Accelerations. We find with 95\% confidence that HR~8799~e is below 13 M_(Jup), the deuterium-fusing mass limit. We derive a hot-start cooling age of 42⁺²⁴₋₁₆\,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 β~Pictoris moving group. We exclude the presence of any additional ≳5-M_(Jup) planets interior to HR~8799~e with semi-major axes between ≈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.
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