Dynamical Mass of the Young Substellar Companion HD 984 B

Abstract Model-independent masses of substellar companions are critical tools to validate models planet and brown dwarf cooling, test their input physics, determine the formation evolution these objects. In this work, we measure dynamical mass orbit young companion HD 984 B. We obtained new high-contrast imaging system with Keck/NIRC2 that expands baseline relative astrometry from 3 8 yr. also present radial velocities host star Habitable-Zone Planet Finder spectrograph at Hobby-Eberly Telescope. Furthermore, exhibits a significant proper motion difference between Hipparcos Gaia EDR3. Our joint fit astrometry, motions, yields 61 ± 4 M Jup for B, placing firmly in regime. The reveals higher eccentricity ( e = 0.76 0.05) compared previous fits. Given broad age constraint 984, is consistent predictions evolutionary models. B’s places it among small but growing list giant direct measurements.