Starlight substructures in dusty, radiative PPDs: limits to the stellar irradiation instability

Disk observations show ubiquitous substructure both at their surface and close to their midplane with gaps, rings, and spirals. While planets often explain such features, substructures are regions of local pressure maxima that can form dust traps, an essential initial condition for dust growth in line with planet formation theories. One proposed mechanism for generating these substructures is stellar-irradiation-driven shadowing, where vertical temperature perturbations cause the disk surface to puff up, casting shadows behind. We investigate the physical conditions for the existence of starlight-driven shadowing and test the viability of this "irradiation instability" argument with radiation hydrodynamical models using the PLUTO code. Our models underscore the importance of consistent modelling of dust dynamics for accurately resolving the irradiation absorption surface. We also produce synthetic scattered light images with RADMC-3D to demonstrate observable signatures, and highlight the role of ELT's capabilities in constraining such shadows and the disk's vertical temperature structure.