Abundance Anomaly of the C Isotopic Species of c-CH in the Low-Mass Star Formation Region L1527
arXiv:1505.03262
Abstract
The rotational spectral lines of c-CH and two kinds of the C isotopic species, c-CCCH ( symmetry) and c-CCCH ( symmetry) have been observed in the 1-3 mm band toward the low-mass star-forming region L1527. We have detected 7, 3, and 6 lines of c-CH, c-CCCH , and c-CCCH, respectively, with the Nobeyama 45 m telescope, and 34, 6, and 13 lines, respectively, with the IRAM 30 m telescope, where 7, 2, and 2 transitions, respectively, are observed with the both telescopes. With these data, we have evaluated the column densities of the normal and C isotopic species. The [c-CH]/[c-CCCH] ratio is determined to be , while the [c-CH]/[c-CCCH] ratio is determined to be . The [c-CH]/[c-CCCH] and [c-CH]/[c-CCCH] ratios expected from the elemental C/C ratio are 60-70 and 30-35, respectively, where the latter takes into account the statistical factor of 2 for the two equivalent carbon atoms in c-CH. Hence, this observation further confirms the dilution of the C species in carbon-chain molecules and their related molecules, which are thought to originate from the dilution of C in the gas-phase C due to the isotope exchange reaction: . Moreover, the abundances of the two C isotopic species are different from each other. The ratio of c- species relative to c- is determined to be . If C were randomly substituted for the three carbon atoms, the [c-]/[c-] ratio would be 0.5. Hence, the observed ratio indicates that c- exists more favorably. Possible origins of the different abundances are discussed.
29 pages, 5 figures. Accepted for publication in ApJ