On the Masses, Ages, and Architectures of Directly Imaged Planets Orbiting Binaries

Direct imaging has revealed a population of giant planets orbiting at wide separations (~100–1000 au) around binaries. The mass ratios of these planets relative to their host binaries range from M_p/M_* ~ 0.1, which is common for stellar multiple systems, down to values of ~0.01 which are more typical of directly imaged planet systems. It is thought that mass ratio may be indicative of differing planet formation mechanisms, with higher mass ratios corresponding to a kind of scaled-down triple-star formation. If so, further clues may be found in these systems’ orbital architectures, and crucially those orbits can also be used to measure dynamical masses and thereby determine ages from evolutionary models. We present results from our long-term Keck adaptive optics orbit monitoring of the binary hosts in two of the highest mass ratio planet-hosting systems: VHS J1256-1257 AB and 2MASS J0249-0557 AB. The highly eccentric orbit that we find for VHS J1256 AB suggests a dynamical origin for its wide companion (a JWST ERS target), and our dynamical mass enables the first precise age dating of this system. At 140±20 Myr, the companion is confirmed to have a mass on the borderline of the deuterium-fusion boundary. The dynamical mass of β Pic moving group member 2MASS J0249 AB offers the first test of substellar evolutionary model-derived ages in a well-characterized young association.