High-contrast interferometry: science cases and measurement approach

The development of high-contrast capabilities has long been recognized as one of the top priorities for the VLTI. As of today, the VLTI achieves routinely contrasts of a few 10-3 in the near-infrared with PIONIER and GRAVITY. Other infrared interferometers in the northern hemisphere have however demonstrated that contrasts of a few 10-4 are within reach using specific data acquisition and reduction techniques. In this paper, we explore the possibility to reach similar or better contrasts on the VLTI. After reviewing the state-of-the-art in high-contrast infrared interferometry, we compare different concepts for a VLTI instrument dedicated to high-contrast imaging in the thermal near-infrared (3-5 microns), a sweet spot to image and characterize young extra-solar planetary systems. We consider key features that made the success of other high-contrast interferometric instruments (e.g., integrated optics, closure/kernel phase, nulling, and statistical data reduction) and describe the expected performance. Finally, we briefly address the science cases, which mainly consist of extrasolar planetary science (exoplanets, exozodiacal disks, and planet-forming regions) and extragalactic astrophysics (AGN and fundamental constants). This project is dubbed Hi-5, for High-contrast Interferometry up to 5 microns.