Institute for Advanced Study / Princeton University Joint Astrophysics Colloquium

I will present a combination of three observational techniques—astrometry, radial velocity, and direct imaging—to discover, weigh, and characterize massive exoplanets and brown dwarfs.  Only a few exoplanets have both measured masses (from radial velocity and astrometry) and atmospheric properties (inferred from spectra), and these have come at a huge cost in telescope time.  By combining recent astrometric measurements from the Gaia satellite with measurements by Hipparcos 35 years ago, we have access to stellar reflex motions that measure the tug of unseen planets and brown dwarfs on their host stars.  These reflex motions have been used both to discover new planets and to weigh known planets and brown dwarfs, even some on centuries-long orbits.  Recent advances include the first images of the sub-300K planet eps Indi b, discovery of the 3 Jupiter mass planet AF Lep b on a Saturn-like orbit, and the discovery that the first brown dwarf imaged, Gl 229B, is itself a binary.  With masses, orbits, and spectra of a growing sample of planets and brown dwarfs, we can build a more complete physical picture of these worlds and connect them to the process of planet formation.