Survey Observations to Study Chemical Evolution from High-mass Starless Cores to High-mass Protostellar Objects. I. HC₃N and HC₅N

Abstract

Abstract We carried out survey observations of HC 3 N and HC 5 N in the 42−45 GHz band toward 17 high-mass starless cores (HMSCs) and 35 high-mass protostellar objects (HMPOs) with the Nobeyama 45 m radio telescope. We have detected HC 3 N from 15 HMSCs and 28 HMPOs, and HC 5 N from 5 HMSCs and 14 HMPOs, respectively. The average values of the column density of HC 3 N are found to be and cm −2 in HMSCs and HMPOs, respectively. The average values of the fractional abundance of HC 3 N are derived to be and in HMSCs and HMPOs, respectively. We find that the fractional abundance of HC 3 N decreases from HMSCs to HMPOs using the Kolmogorov–Smirnov test. On the other hand, its average value of the column density slightly increases from HMSCs to HMPOs. This may imply that HC 3 N is newly formed in dense gas in HMPO regions. We also investigate the relationship between the column density of HC 3 N in HMPOs and the luminosity-to-mass ratio ( L / M ), a physical evolutional indicator. The column density of HC 3 N tends to decrease with the increase of the L / M ratio, which suggests that HC 3 N is destroyed by the stellar activities.