Abundance anomaly of the 13C species of CCH

Aims. We have observed the N = 1-0 lines of CCH and its C-13 isotopic species toward a cold dark cloud, TMC-1 and a star-forming region, L1527, to investigate the C-13 abundances and formation pathways of CCH. Methods. The observations have been carried out with the IRAM 30 m telescope. Results. We have successfully detected the lines of (CCH)-C-13 and (CCH)-C-13 toward the both sources and found a significant intensity difference between the two C-13 isotopic species. The [(CCH)-C-13]/[(CCH)-C-13] abundance ratios are 1.6 +/- 0.4 (3 sigma) and 1.6 +/- 0.1 (3 sigma) for TMC-1 and L1527, respectively. The abundance difference between (CCH)-C-13 and (CCH)-C-13 means that the two carbon atoms of CCH are not equivalent in the formation pathway. On the other hand, the [CCH]/[(CCH)-C-13] and [CCH]/[(CCH)-C-13] ratios are evaluated to be larger than 170 and 250 toward TMC-1, and to be larger than 80 and 135 toward L1527, respectively. Therefore, both of the C-13 species are significantly diluted in comparison with the interstellar C-12/C-13 ratio of 60. The dilution is discussed in terms of a behavior of C-13 in molecular clouds.