Probing the disks around young stellar objects at (sub-)astronomical unit scale with VLTI/GRAVITY
Abstract: Deciphering the physical processes occurring in the inner region of protoplanetary disks is key to understand the environmental conditions of (terrestrial) planet formation and evolution. Thanks to its unique milliarcsecond angular resolution, VLTI/GRAVITY has studied the ~0.1 – 5AU disk region in a homogeneous sample of nearly hundred young stellar objects covering the T-Tauri (~40), Herbig AeBe (~60), and high-mass YSO (a few) classes. The K-band GRAVITY YSO survey started 8 years ago has made significant contributions to the field: we extended the infrared disk radius-luminosity relation over four orders of magnitude, which has permitted to evidence trends with the properties of the central star (mass, accretion rate); we tested possible evolutionary states using disk morphology proxies; we evidenced the month-scale morphological variability of the inner disk for few sources. We finally discuss the potential yield of the new GRAVITY+ upgrade, in particular towards the study of early Class I phases of YSOs in various star forming regions, as well as the possible legacy of GRAVITY(+) observations to refine theoretical models of protoplanet.