The H 13 CN/HC 15 N Abundance Ratio in Dense Cores: Possible Source‐to‐Source Variation of Isotope Abundances?

Abstract

We have observed the H13CN (J=1-0) and HC15N(J=1-0) lines simultaneously toward three dense cores in the Taurusmolecular cloud complex and have found a significant source-to-sourcevariation of the column density ratio,N(H13CN)/N(HC15N). The lowest ratio of 2.6-3.1 isobserved toward L1521E, while the highest ratio of 8-11 is observedtoward L1498. We have also observed the 12C18O(J=1-0, 2-1) and 13C18O (J=1-0) lines, and the12C/13C ratio has been derived to be 58.8+/-3.7and >=117 toward L1521E and L1498, respectively. These results implythat a substantial isotope fractionation effect may exist in theformation processes of these molecules, or elemental abundances are notuniform among the observed sources. If the source-to-source variation ofthe (14N/15N)/(12C/13C)ratio in HCN and the 12C/13C ratio in COoriginates from the elemental abundance variation, the14N/15N ratio is calculated to be 151+/-16 and>=813 for L1521E and L1498, respectively. These ratios significantlydeviate from the values obtained toward Galactic disk sources.