Gaia-Binaries: formation and fundamental properties of stars and planetary systems
Systems with close stellar-mass or planetary-mass companions are ubiquities in the universe. However, the processes that shape the architecture of these systems are still not understood. By 2021 the GAIA mission will provide astrometric+radial velocity orbits for millions of multiple systems. For the vast majority, GAIA will measure only photocenter displacements and not be able to resolve the individual components, preventing masses and orbital statistics to be derived.  The aim of the GAIA-BIFROST project is to exploit the GAIA sample in order to identify the processes that govern the formation and dynamical evolution of binaries and planetary systems. Using VLTI+CHARA interferometry we will resolve up to ∼6000 GAIA binaries in the continuum and in spectral lines, allowing us: (a) to derive precision dynamical masses, ages, and comprehensive orbital parameter statistics that is needed to discern between different binary formation scenarios; (b) to measure the spin-orbit and spin-spin alignment for hundreds of GAIA star-star and star-planet systems. This will constrain the origin of the orbit obliquity for stars and planets, providing unique information about their formation process and dynamical history; and (c) to image companion-disk interactions in young binary systems and use them as benchmark for studying the hydrodynamical processes that determine the system architecture at formation.  Furthermore, our survey will provide a legacy data set of dynamical masses and precision ages for (literally!) thousands of stars, by far exceeding all earlier work in these areas. This will impact many areas of modern astrophysics, including studies on stellar evolution and Galactic Archaeology. To unlock these powerful new observational avenues, it is important to resolve GAIA binaries close to the GAIA wavebands and at high spectral resolution. We will achieve this by commissioning the BIFROST beam combiner at VLTI, building on our recent successful instrumentation work