HCN and HNC abundance ratio toward three different phases of massive star formation

In the process of star formation, the density and temperature of associated material, which are the physical conditions for the molecular chemistry, vary dramatically. As a result, the connection between physical and chemical conditions has been used to trace the evolutionary stages in star formation. One chemical tracer for the physical conditions in star forming material is the [HCN]/[HNC] abundance ratio since the ratio strongly depends on the kinetic temperature in molecular clouds. Here we investigate the [HCN]/[HNC] abundance ratios in objects related to the massive star formation. For the investigation, we carried out $H^{13}CN$ and $HN^{13}C$ line observation toward objects in three different evolutionary stages of massive star formation: Infrared dark clouds (IRDCs), High-mass protostellar object (HMPOs), and Ultra-compact HII regions (UCHIIs). According to our observational results, both $H^{13}CN$ and $HN^{13}C$ lines have been detected toward 19 IRDCs, 25 HMPOs, and 31 UCHIIs. We will discuss about the [HCN]/[HNC] abundance ratios in different evolutionary stages of massive star formation and associate the results with the physical conditions of the targets.