Effect of Optical Depth on Study of Chemical Properties of Massive Star Forming Clumps

Here we present the study on chemical properties of massive star forming clumps using N $ _2 $ H $ ^+ $ (1-0), H $ ^{13} $ CO $ ^+ $ (1-0), HCN(1-0) and HN $ ^{13} $ C(1-0) data from the literature [Astron. Astrophys. 563, A97 (2014)]. We found that abundances of H $ ^{13} $ CO $ ^+ $ and HN $ ^{13} $ C are affected by H $ _2 $ column densities. As the median values of these two abundances increase by nearly 10 times from stages A to B, H $ ^{13} $ CO $ ^+ $ and HN $ ^{13} $ C are suitable for tracing the evolution of massive star forming clumps. The order of rapidity in growth of abundances of all the four studied molecules from stages A to B, is H $ ^{13} $ CO $ ^+ $ , HCN, HN $ ^{13} $ C, and N $ _2 $ H $ ^+ $ , from the highest to the lowest. Our results suggest that the observing optically thin molecular lines with high angular resolution are necessary to study the chemical evolution of massive star forming clumps.