Abundance anomaly of the {sup 13}C isotopic species of c-C{sub 3}H{sub 2} in the low-mass star formation region L1527
- Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)
- Nobayama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)
- Université de Grenoble Alpes, IPAG, F-38000 Grenoble (France)
- Observatorio Astronómico Nacional (OAN, IGN), Calle Alfonso XII 3, E-28014 Madrid (Spain)
- Université de Toulouse, UPS-OMP, IRAP, Toulouse (France)
The rotational spectral lines of c-C{sub 3}H{sub 2} and two kinds of the {sup 13}C isotopic species, c-{sup 13}CCCH{sub 2} (C{sub 2v} symmetry) and c-CC{sup 13}CH{sub 2} (C{sub s} 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-C{sub 3}H{sub 2}, c-{sup 13}CCCH{sub 2}, and c-CC{sup 13}CH{sub 2}, respectively, with the Nobeyama 45 m telescope and 34, 6, and 13 lines, respectively, with the IRAM 30 m telescope, where seven, two, and two transitions, respectively, are observed with both telescopes. With these data, we have evaluated the column densities of the normal and {sup 13}C isotopic species. The [c-C{sub 3}H{sub 2}]/[c-{sup 13}CCCH{sub 2}] ratio is determined to be 310 ± 80, while the [c-C{sub 3}H{sub 2}]/[c-CC{sup 13}CH{sub 2}] ratio is determined to be 61 ± 11. The [c-C{sub 3}H{sub 2}]/[c-{sup 13}CCCH{sub 2}] and [c-C{sub 3}H{sub 2}]/[c-CC{sup 13}CH{sub 2}] ratios expected from the elemental {sup 12}C/{sup 13}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-C{sub 3}H{sub 2}. Hence, this observation further confirms the dilution of the {sup 13}C species in carbon-chain molecules and their related molecules, which are thought to originate from the dilution of {sup 13}C{sup +} in the gas-phase C{sup +} due to the isotope exchange reaction: {sup 13}C{sup +}+CO→{sup 13}CO+C{sup +}. Moreover, the abundances of the two {sup 13}C isotopic species are different from each other. The ratio of c-{sup 13}CCCH{sub 2} species relative to c-CC{sup 13}CH{sub 2} is determined to be 0.20 ± 0.05. If {sup 13}C were randomly substituted for the three carbon atoms, the [c-{sup 13}CCCH{sub 2}]/[c-CC{sup 13}CH{sub 2}] ratio would be 0.5. Hence, the observed ratio indicates that c-CC{sup 13}CH{sub 2} exists more favorably. Possible origins of the different abundances are discussed.
- OSTI ID:
- 22882958
- Journal Information:
- Astrophysical Journal, Vol. 807, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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