Abundance anomaly of the ¹³C species of CCH

¹ Department of Physics and Research Center for the Early Universe, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan e-mail: [nami;osamu]@taurus.phys.s.u-tokyo.ac.jp; yamamoto@phys.s.u-tokyo.ac.jp
² Institute of Astronomy, The University of Tokyo, Osawa, Mitaka, Tokyo, 181-8588, Japan e-mail: sakai@ioa.s.u-tokyo.ac.jp
³ Nobeyama Radio Observatory and Graduate University for Advanced Studies, Minamimaki, Minamisaku, Nagano 384-1305, Japan e-mail: stakano@nro.nao.ac.jp

Received: 10 August 2009
Accepted: 15 December 2009

Abstract

Aims. 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.

Methods. The observations have been carried out with the IRAM 30 m telescope.

Results. 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.