Imaging the Dynamical Imprints of Planet Formation in Protoplanetary Discs

Planet formation is a complex process that takes place in the discs around young stars. The dominant fraction of the planet population is believed to form in the inner few astronomical units of these discs. Therefore, it is essential to study the physical processes that take place in these inner disc regions to unveil the initial conditions of planet formation. This will also advance our understanding of how Earth formed and how is able to develop the right conditions for harboring life, addressing one of the oldest questions of mankind. Detailed imaging of the inner disc environment might also reveal planets that are currently in the process of formation and that could be detectable either through the emission from circumplanetary accretion processes, or through the gravitational influence that these planets exert on the disc. Observational studies of planet formation in protoplanetary discs are primarily limited by the achieved angular resolution that is set by the telescope diameter. Accordingly, most studies of protoplanetary discs could only investigate the outer disc regions, on scales of tens to hundreds of astronomical units. Infrared interferometry offers an elegant way to overcome this resolution barrier by coherently combining the light from separate smaller telescopes that can be spread over hundreds of metres, thereby providing the first direct view into the innermost astronomical unit of protoplanetary discs. The key requirement for obtaining direct images with infrared interferometers is the number of telescopes that are combined, which has so far been limited to 4 telescopes for protoplanetary disc observations. The primary objective of the ERC Starting Grant is to push this barrier by equipping the MIRC beam combiner at the CHARA telescope array with an innovative ultra-low read-noise detector system that will permit us to obtain first 6-telescope interferometric observations of low- and intermediate-mass young stars. Increasing from 4 telescopes to 6 telescopes provides 3.5-times more observables per measurements, while the CHARA array will also provide us about 2.5-times longer baselines than what was achieved in earlier observations. This will enable us to obtain an image in a single night of observing and to study also the time evolution of any resolved structures. We will use the observational capabilities that will result from our CHARA instrumentation work in order to search for possibly planet-induced structures in the inner regions of protoplanetary discs and to image their temporal evolution. We will combine the interferometric data obtained over a wide wavelength range (near-infrared, mid-infrared to sub-millimetre wavelengths) in order to characterise the resolved structures. Finally, we will search for the signatures of the planets themselves by imaging in accretion-tracing spectral lines. Some selected results from this project include: Kraus et al., Science, in press: "A triple star system with a misaligned and warped circumstellar disk shaped by disk tearing" Kraus et al. (2020, ApJL 897, 8): "Spin-Orbit Alignment of the Beta Pictoris Planetary System" Davies et al. (2020, ApJ 897, 31): "The Inner Disk of RY Tau: Evidence of Stellar Occultation by the Disk Atmosphere at the Sublimation Rim from K-band Continuum Interferometry" Kreplin et al. (2020, MNRAS 492, 566): "First NIR interferometrically resolved high-order Brackett and forbidden Fe lines of a B[e] star: V921 Sco" Kluska et al. (2020, A&A 636, A116): "A family portrait of disk inner rims around Herbig Ae/Be stars. Hunting for warps, rings, self shadowing, and misalignments in the inner astronomical units" Labdon et al. (2019, A&A 627, A36): "Dusty disk winds at the sublimation rim of the highly inclined, low mass young stellar object SU Aurigae" Hone et al. (2019, A&A 623, A38): "Compact gaseous accretion disk in Keplerian rotation around MWC 147" Davies et al. (2018, ApJ 866, 23): "Simultaneous Spectral Energy Distribution and Near-infrared Interferometry Modeling of HD142666" Kraus et al. (2017, ApJL 848, L11): "Dust-trapping Vortices and a Potentially Planet-triggered Spiral Wake in the Pre-transitional Disk of V1247 Orionis" Kraus et al. (2017, ApJL 835, 5): "A High-mass Protobinary System with Spatially Resolved Circumstellar Accretion Disks and Circumbinary Disk" Hone et al. (2017, A&A 607, 17): "Gas dynamics in the inner few AU around the Herbig B[e] star MWC297. Indications of a disk wind from kinematic modeling and velocity-resolved interferometric imaging" Kreplin et al. (2016, A&A 590, 96): "Resolving the inner disk of UX Orionis" Kraus et al. (2016, MNRAS 462, 61): "V346 Normae: first post-outburst observations of an FU Orionis star" This project is funded by the European Research Council (Grant Agreement No. 639889).