Mapping Observations of DNC and HNC in Dark Cloud Cores

We present results of mapping observations of the DNC, HNC, and HCO lines (J=1-0) toward 4 nearby dark cloud cores, TMC-1, L1512, L1544, and L63, along with observations of the DNC and HNC lines (J=21) toward selected positions. By use of statistical equilibrium calculations based on the LVG model, the H2 densities are derived to be (1.4-5.5)×10 5 cm, and the [DNC]/[HNC] ratios are derived to be 1.25-5.44 with a typical uncertainty by a factor of 2. The observed [DNC]/[HNC] ratios range from 0.02 to 0.09, assuming the [C]/[C] ratio of 60. Distributions of DNC and HNC are generally similar to each other, whereas the distribution of HCO is more extended than those of DNC and HNC, indicating that they reside in an inner part of the cores than HCO. The [DNC]/[HNC] ratio is rather constant within each core, although a small systematic gradients are observed in TMC-1 and L63. Particularly, no such systematic gradient is found in L1512 and L1544, where a significant effect of depletion of molecules is reported toward the central part of the cores. This suggests that the [DNC]/[HNC] ratio would not be very sensitive to depletion factor, unlike the [DCO]/[HCO] Current address: Earth Rotation Division, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan; [email protected]