The H13CN/HC15N Abundance Ratio in Dense Cores: Possible Source‐to‐Source Variation of Isotope Abundances?

We have observed the H 13 CN ( J = 1-0) and HC 15 N ( J = 1-0) lines simultaneously toward three dense cores in the Taurus molecular cloud complex and have found a significant source-to-source variation of the column density ratio, N (H 13 CN)/ N (HC 15 N). The lowest ratio of 2.6-3.1 is observed toward L1521E, while the highest ratio of 8-11 is observed toward L1498. We have also observed the 12 C 18 O ( J = 1-0, 2-1) and 13 C 18 O ( J = 1-0) lines, and the 12 C/ 13 C ratio has been derived to be 58.8 ± 3.7 and ≥117 toward L1521E and L1498, respectively. These results imply that a substantial isotope fractionation effect may exist in the formation processes of these molecules, or elemental abundances are not uniform among the observed sources. If the source-to-source variation of the ( 14 N/ 15 N)/( 12 C/ 13 C) ratio in HCN and the 12 C/ 13 C ratio in CO originates from the elemental abundance variation, the 14 N/ 15 N ratio is calculated to be 151 ± 16 and ≥813 for L1521E and L1498, respectively. These ratios significantly deviate from the values obtained toward Galactic disk sources.