CO, CI and CII observations of NGC 7023

We present new data on the photodissociation regions associated with the reflection nebula NGC7023. 13CO(3-2) emission, delineates a molecular cloud containing a cavity largely devoid of molecular gas around this star. Neutral carbon is closely associated with the 13CO emission while ionized carbon is found inside and at the edges of the cavity. The ionized carbon appears to be, at least in part, associated with HI. We have mapped the northern and southern rims in 12CO(6-5) emission and found a good association with the H2 rovibrational emission, though the warm CO gas permeates a larger fraction of the molecular cloud than the vibrationally excited H2. The results are compared with PDR models. We suggest that a second PDR has been created at the surface of the molecular cloud by the scattered radiation from HD 200775. This second PDR produces a layer of atomic carbon at the surface of the sheet, which increases the predicted [C]/[CO] abundance ratio to 10%, close to the observed value.