1/27/2020

Physical-chemical models have long demonstrated that UV photons play an important role in regulating gas-phase chemistry in surface layers of protoplanetary disks. To examine the relationship between CN and HCN gas distributions and photocatalyzing UV radiation fields, we analyze a sample of ~15 young stars in the Lupus and Taurus-Auriga star-forming regions through new and archival HST, Spitzer, ALMA, SMA, and IRAM data. LyA emission and the FUV continuum, which are both responsible for dissociating relevant molecular species, were measured from the HST spectra and compared to observed CN and HCN fluxes. We find a significant positive correlation between the FUV continuum fluxes and 14 micron HCN emission, consistent with models requiring photodissociation of molecular nitrogen to trigger the main CN and HCN formation pathways. We also report a tentative negative correlation between HCN and LyA emission, indicating LyA-driven photodissociation of HCN molecules in the inner disk. To further investigate the observational relationship between UV radiation fields and molecular gas distributions, we use physical-chemical models to reproduce emission from both sub-mm CN and UV-fluorescent H2. Preliminary results constrain the amount of UV flux required to re-produce both sets of observations, implying that modeling the two features together may break the degeneracy between disk flaring and irradiation of gas surface layers.