Mapping Observations of DNC and HN13C in Dark Cloud Cores
Mapping Observations of DNC and HN13C in Dark Cloud Cores
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DOI：
10.1086/376970
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发表时间：
2001-02
期刊：
影响因子：
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通讯作者：
T. Hirota;Masafumi Ikeda;S. Yamamoto
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文献类型：
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作者：
T. Hirota;Masafumi Ikeda;S. Yamamoto
我们提供了DNC、HN 13 C和H13 CO+谱线（J = 1-0）对四个邻近暗云核TMC-1、L1512、L1544和L 63的测绘观测结果，沿着DNC和HN 13 C谱线（J = 2-1）对选定位置的观测结果。利用基于大速度梯度（LVG）模型的统计平衡计算，得到H2密度为× 105 cm-3，[DNC]/[HN 13 C]比值为1.25-5.44，典型不确定度为2倍。假设[12 C]/[13 C]比为60，观察到的[DNC]/[HNC]比范围为0.02至0.09。DNC和HN 13 C的分布基本相似，而H13 CO+的分布比DNC和HN 13 C的分布更广，表明它们比HCO+位于核的更向内的部分。虽然在TMC-1和L 63中观察到小的系统梯度，但[DNC]/[HN 13 C]比率在每个岩心内相当恒定。特别是，在L1512和L1544中没有发现这种系统梯度，其中报告了朝向核的中心部分的分子耗尽的显著效果。这表明，与[DCO+]/[HCO+]比不同，[DNC]/[HNC]比对耗竭因子不太敏感。另一方面，[DNC]/[HNC]比的核与核的变化，其范围超过一个数量级，比每个核内的变化更显着。这些结果定性解释的三个竞争的时间依赖性过程的组合：气相氘分馏，耗尽到晶粒表面的分子，和动态演变的核心。
We present results of mapping observations of the DNC, HN13C, and H13CO+ lines (J = 1-0) toward four nearby dark cloud cores, TMC-1, L1512, L1544, and L63, along with observations of the DNC and HN13C lines (J = 2-1) toward selected positions. By use of statistical equilibrium calculations based on the large velocity gradient (LVG) model, the H2 densities are derived to be × 105 cm-3, and the [DNC]/[HN13C] ratios are derived to be 1.25-5.44, with a typical uncertainty of a factor of 2. The observed [DNC]/[HNC] ratios range from 0.02 to 0.09, assuming a [12C]/[13C] ratio of 60. Distributions of DNC and HN13C are generally similar to each other, whereas the distribution of H13CO+ is more extended than those of DNC and HN13C, indicating that they reside in a more inward part of the cores than HCO+. The [DNC]/[HN13C] ratio is rather constant within each core, although small systematic gradients are observed in TMC-1 and L63. In particular, 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 the depletion factor, unlike the [DCO+]/[HCO+] ratio. On the other hand, the core-to-core variation of the [DNC]/[HNC] ratio, which ranges over an order of magnitude, is more remarkable than the variation within each core. These results are interpreted qualitatively by a combination of three competing time-dependent processes: gas-phase deuterium fractionation, depletion of molecules onto grain surfaces, and dynamical evolution of a core.