${}^{13}$C Isotopic Fractionation of CCH in Two Starless Cores: L1521B and L134N

Abstract

We have carried out observations of CCH and its two ${}^{13}$C isotopologues, ${}^{13}$CCH and C${}^{13}$CH, in the 84 - 88 GHz band toward two starless cores, L1521B and L134N (L183), using the Nobeyama 45 m radio telescope. We have detected C${}^{13}$CH with a signal-to-noise (S/N) ratio of 4, whereas no line of ${}^{13}$CCH was detected in either the dark clouds. The column densities of the normal species were derived to be ($1.66\pm 0.18$)$\times 10^{14}$ cm${}^{-2}$ and ($7.3\pm 0.9$)$\times 10^{13}$ cm${}^{-2}$ ($1\sigma$) in L1521B and L134N, respectively. The column density ratios of $N$(C${}^{13}$CH)/$N$(${}^{13}$CCH) were calculated to be $>1.1$ and $>1.4$ in L1521B and L134N, respectively. The characteristic that ${}^{13}$CCH is less abundant than C${}^{13}$CH is likely common for dark clouds. Moreover, we find that the ${}^{12}$C/${}^{13}$C ratios of CCH are much higher than those of HC${}_3$N in L1521B by more than a factor of 2, as well as in Taurus Molecular Cloud-1 (TMC-1). In L134N, the differences in the ${}^{12}$C/${}^{13}$C ratios between CCH and HC${}_3$N seem to be smaller than those in L1521B and TMC-1. We discuss the origins of the ${}^{13}$C isotopic fractionation of CCH and investigate possible routes that cause the significantly high ${}^{12}$C/${}^{13}$C ratio of CCH especially in young dark clouds, with the help of chemical simulations. The high ${}^{12}$C/${}^{13}$C ratios of CCH seem to be caused by reactions between hydrocarbons (e.g., CCH, C${}_2$H${}_2$, $l,c$-C${}_3$H) and C${}^{+}$.

Accepted for publication in The Astrophysical Journal, 15 pages, 6 figures, 5 tables

References in corpus (9)

• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• The effect of uncertainties on chemical models of dark clouds
• Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies
• Modeling the Lukewarm Corino Phase - is L1527 unique?
• Detection of HC${}_5$N and HC${}_7$N Isotopologues in TMC-1 with the Green Bank Telescope
• 13C Isotopic Fractionation of HC3N in Star-Forming Regions -Low-Mass Star Forming Region L1527 and High-Mass Star Forming Region G28.28-0.36-
• ${}^{13}$C isotopic fractionation of HC${}_3$N in two starless cores: L1521B and L134N (L183)
• Survey Observations to Study Chemical Evolution from High-Mass Starless Cores to High-Mass Protostellar Objects II. HC${}_3$N and N${}_2$H${}^{+}$
• First Detection of HC${}_5$${}^{15}$N in the Interstellar Medium

Cited by in corpus (8)

• Carbon isotopic fractionation in molecular clouds
• Carbon-Chain Chemistry in the Interstellar Medium
• Formation of S-bearing complex organic molecules in interstellar clouds via ice reactions with C2H2, HS, and atomic H
• The First Mid-Infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment Towards the Orion Hot Core
• Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
• Carbon Chain Chemistry in Hot-Core Regions around Three Massive Young Stellar Objects Associated with 6.7 GHz Methanol Masers
• Carbon-chain molecule survey toward four low-mass molecular outflow sources
• Investigation of Chemical Differentiation among the NGC2264 Cluster-Forming Clumps