Deuterium Fractionation Survey Toward Protostellar Sources in the Perseus Molecular Cloud: HNC Case

A survey observation of the DNC (J = 1-0 and J = 3-2) and HN¹³C (J = 1-0 and J = 3-2) emission toward 34 Class 0 and I protostellar sources in the Perseus molecular cloud has been conducted with the NRO 45 m and IRAM 30 m telescopes to explore how the deuterium ratio of the neutral species changes after the birth of a protostar. We have detected the J = 1-0 and J = 3-2 lines of DNC toward 32 sources and the J = 1-0 and J = 3-2 lines of HN¹³C toward 31 and 26 sources, respectively. A mean deuterium ratio of HNC, which is defined as R _D(HNC) = N(DNC)/N(HNC), is found to be 0.049-0.056. We compare R _D(HNC) with physical parameters of the sources, and find a negative correlation between R _D(HNC) and the bolometric temperature. This result suggests that R _D(HNC) decreases as a protostar evolves. Compared with the deuterium ratio of the molecular ion {{{N}}}₂{{{H}}}⁺, R _D(HNC) seems to decrease slowly with the protostellar evolution.