Precise Observations of the 12C/13C Ratios of HC3N in the Low-mass Star-forming Region L1527

Using the Green Bank 100 m telescope and the Nobeyama 45 m telescope, we have observed the rotational emission lines of the three ¹³C isotopic species of HC₃N in the 3 and 7 mm bands toward the low-mass star-forming region L1527 in order to explore their anomalous ¹²C/¹³C ratios. The column densities of the ¹³C isotopic species are derived from the intensities of the J = 5-4 lines observed at high signal-to-noise ratios. The abundance ratios are determined to be 1.00:1.01 ± 0.02:1.35 ± 0.03:86.4 ± 1.6 for [H¹³CCCN]:[HC¹³CCN]:[HCC¹³CN]:[HCCCN], where the errors represent one standard deviation. The ratios are very similar to those reported for the starless cloud Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP). These ratios cannot be explained by thermal equilibrium, but likely reflect the production pathways of this molecule. We have shown the equality of the abundances of H¹³CCCN and HC¹³CCN at a high-confidence level, which supports the production pathways of HC₃N via C₂H₂ and {{{C}}}₂{{{{H}}}₂}⁺. The average ¹²C/¹³C ratio for HC₃N is 77 ± 4, which may be only slightly higher than the elemental ¹²C/¹³C ratio. Dilution of the ¹³C isotope in HC₃N is not as significant as that in CCH or c-C₃H₂. We have also simultaneously observed the DCCCN and HCCC¹⁵N lines and derived the isotope ratios [DCCCN]/[HCCCN] = 0.0370 ± 0.0007 and [HCCCN]/[HCCC¹⁵N] = 338 ± 12.