Abstract
We have observed the H13CN (J = 1-0) and HC15N (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(H13CN)/N(HC15N). 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 12C18O (J = 1-0, 2-1) and 13C18O (J = 1-0) lines, and the 12C/13C 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 (14N/15N)/(12C/13C) ratio in HCN and the 12C/13C ratio in CO originates from the elemental abundance variation, the 14N/15N 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.
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