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 N2H+, RD(HNC) seems to decrease slowly with the protostellar evolution.
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