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 C-13 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 C-12/C-13 ratios. The column densities of the C-13 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 [(HCCCN)-C-13]:[(HCCCN)-C-13]:[(HCCCN)-C-13]: [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 (HCCCN)-C-13 and (HCCCN)-C-13 at a high-confidence level, which supports the production pathways of HC3N via C2H2 and C2H2+. The average C-12/C-13 ratio for HC3N is 77 +/- 4, which may be only slightly higher than the elemental C-12/C-13 ratio. Dilution of the C-13 isotope in HC3N is not as significant as that in CCH or c-C3H2. We have also simultaneously observed the DCCCN and HCCC15 N lines and derived the isotope ratios [DCCCN]/[HCCCN] = 0.0370 +/- 0.0007 and [HCCCN]/[(HCCCN)-N-15] = 338 +/- 12.