JWST-DECO: The Impact of Accretion on Mid-infrared Observable Water in Planet-forming Disks

The inner few astronomical units of a protoplanetary disk host the majority of observed exoplanets and are the primary planet-forming zone of the disk. The mid-IR spectra of disks, with their rich forest of water lines, provide key insights into the composition of forming planets. One of the strongest trends seen with data from Spitzer and now JWST is a correlation between the increase in water line flux and the accretion luminosity of a system. We set out to reproduce and understand this trend by adding an accretion module to the thermochemical code DALI, and we explore how viscous accretion heating and the addition of accretion luminosity impact the 2D temperature structure and the observable water reservoir. We reproduce the trend that the observed water mass increases with accretion rate, with hot, warm, and cool water being more to less strongly correlated, respectively. Our model suggests that these trends are due to an increased emitting area with accretion rate, with some of the cool and warm population becoming hidden underneath an optically thick dust surface and being constrained to a smaller disk volume. This trend is driven by the accretion-related increase in central luminosity, while viscous heating centralized to the midplane has no impact on observed water mass. This analysis provides the necessary framework for future interpretation of JWST spectral features in the context of disk, stellar, and environmental properties.