2010A&A...512A..31S

We have observed the N=1-0 lines of CCH and its ¹³C isotopic species toward a cold dark cloud, TMC-1 and a star-forming region, L1527, to investigate the ¹³C abundances and formation pathways of CCH. The observations have been carried out with the IRAM 30m telescope. We have successfully detected the lines of ¹³CCH and C¹³CH toward the both sources and found a significant intensity difference between the two ¹³C isotopic species. The [C¹³CH]/[¹³CCH] abundance ratios are 1.6 ±0.4 (3σ) and 1.6 ±0.1 (3σ) for TMC-1 and L1527, respectively. The abundance difference between C¹³CH and ¹³CCH means that the two carbon atoms of CCH are not equivalent in the formation pathway. On the other hand, the [CCH]/[C¹³CH] and [CCH]/[¹³CCH] 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 ¹³C species are significantly diluted in comparison with the interstellar ¹²C/¹³C ratio of 60. The dilution is discussed in terms of a behavior of ¹³C in molecular clouds.