Chemical Modeling of the Innermost Regions of Protoplanetary Disks

Planetesimal formation occurs in the optically thick mid-plane of protoplanetary disks. If planetesimals sequester material that is rich in volatile (C, O, S, N) and refractory (e.g., Fe, Si, Al) elements, then these abundances originating from the innermost disk regions (R_disk ≤ 0.2 AU) are expected to be significantly depleted. Additionally, dust traps can further deplete these elements. We present a physical-chemical model that predicts atomic emission line ratios, given a range of depletion factors and mid-plane densities (15.75 ≤ log(n_H [cm^-3]) ≤ 16.25). We use the photoionization and chemistry code Cloudy (v25.00) to create a 1D radial slab model of the innermost disk within the dust sublimation rim of a classical T Tauri system. Our model can be applied to observed line ratios in disks in order to determine if rocky planet formation has begun.