High abundance ratio of ${}^{13}$CO to C${}^{18}$O toward photon-dominated regions in the Orion-A giant molecular cloud

Yoshito Shimajiri, Yoshimi Kitamura, Masao Saito +11

Aims. We derive physical properties such as the optical depths and the column densities of ${}^{13}$CO and C${}^{18}$O to investigate the relationship between the far ultraviolet (FUV)…