2002ApJ...575..250I

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.