Abstract
In this talk, I will present two applications of long time-baseline astrometric accelerations from Hipparcos and Gaia to direct imaging of exoplanets and brown dwarfs. I’ll first discuss the measurement of a dynamical mass of the brown dwarf HD 984 B. The masses of directly-imaged substellar objects are traditionally inferred from their age and luminosity through low-temperature cooling models. This leads to highly uncertain masses that are dependent on the choice of model and initial conditions assumed. Model-independent, dynamical masses provide a valuable empirical test of these models and their underlying physics. These gold standards are difficult to obtain; only ten brown dwarfs and giant planets have dynamical masses. HD 984 exhibits a proper motion change between Hipparcos and Gaia, which enables us to measure the dynamical mass of its brown dwarf companion, in conjunction with relative orbital motion. To enable effective orbit fitting, we obtained a new epoch of the system with NIRC2 on Keck in July, 2019. I will report on the current status of this measurement and the reduction of the new observation. I’ll then briefly discuss the beginnings of a survey of young, accelerating systems to search for new giant planet companions. Large direct-imaging surveys have revealed that giant planets on wide orbits are rare, with occurrence rates around 1%. Astrometric accelerations present the opportunity to improve these outcomes by focusing future campaigns on stars that exhibit astrometric reflux motion consistent with the existence of a companion. We are currently commencing a survey of promising accelerating systems. I’ll discuss the structure of this survey and some of the considerations made in constructing the sample.
