NEW DETECTIONS OF HNC IN PLANETARY NEBULAE: EVOLUTION OF THE [HCN]/[HNC] RATIO
NEW DETECTIONS OF HNC IN PLANETARY NEBULAE: EVOLUTION OF THE [HCN]/[HNC] RATIO
复制标题
行星状星云中 HNC 的新发现：[HCN]/[HNC] 比率的演变
DOI：
10.3847/1538-4357/835/1/79
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
L. Ziurys
中科院分区：
文献类型：
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作者：
D. Schmidt;L. Ziurys
在11个行星状星云（PNe）中发现了HNC，包括K4-47、K3-58、K3-17、M3-28和M4-14。这些来源，代表了广泛的年龄和形态，以前观察到的HCN的施密特和Ziurys。使用亚利桑那射电天文台的新12米和亚毫米望远镜测量了90和271 GHz附近HNC的J = 1 → 0和J = 3 → 2跃迁。HCN和HNC也通过它们的J = 1 → 0线被识别出来，这些线位于星云（NGC 7293）的八个位置。HNC的柱密度由辐射传输模型确定，为Ntot（HNC）<$（0.06-4.0）× 1013 cm−2，对应于相对于H2的丰度分数f <$（0.02-1.4）× 10−7。在整个海平面上，HCN和HNC的柱密度分别为N tot（HCN）<$（0.2-2.4）× 1012 cm−2和N tot（HNC）<$（0.07-1.6）× 1012 cm−2，丰度分别为（0.2-3.2）× 10−7和（0.09-2.2）× 10−7。所有PNe的[HCN]/[HNC]比值在1.1 -8之间变化，整个障碍物的[HCN]/[HNC]比值为1.1 -4。这些数值与在渐近巨星分支星中发现的数值相比大大降低了，在渐近巨星中的比值通常大于100。与化学模型的预测相反，HNC的丰度和[HCN]/[HNC]的比值在10,000年的时间跨度内似乎并没有随着星云年龄的变化而显着变化。HNC的增加似乎出现在原行星阶段，但一旦达到PN阶段就变得“冻结”。
New detections of HNC have been made toward 11 planetary nebulae (PNe), including K4-47, K3-58, K3-17, M3-28, and M4-14. These sources, which represent a wide range of ages and morphologies, had previously been observed in HCN by Schmidt & Ziurys. Measurements of the J = 1 → 0 and J = 3 → 2 transitions of HNC near 90 and 271 GHz were conducted using the new 12 m and the Sub-Millimeter Telescope of the Arizona Radio Observatory. HCN and HNC were also identified via their J = 1 → 0 lines toward eight positions across the Helix Nebula (NGC 7293). Column densities for HNC, determined from radiative transfer modeling, were Ntot(HNC) ∼ (0.06–4.0) × 1013 cm−2, corresponding to fractional abundances with respect to H2 of f ∼ (0.02–1.4) × 10−7. The HCN and HNC column densities across the Helix were found to be N tot ( HCN ) ∼ (0.2–2.4) × 1012 cm−2 and N tot ( HNC ) ∼ (0.07–1.6) × 1012 cm−2, with fractional abundances of (0.2–3.2) × 10−7 and (0.09–2.2) × 10−7. The [HCN]/[HNC] ratio varied between ∼1–8 for all PNe, with [HCN]/[HNC] ∼1–4 across the Helix. These values are greatly reduced from what has been found in asymptotic giant branch stars, where the ratio is typically >100. Both the abundance of HNC and the [HCN]/[HNC] ratio do not appear to vary significantly with nebular age across a time span of ∼10,000 years, in contrast to predictions of chemical models. The increase in HNC appears to arise in the proto-planetary stage, but becomes “frozen” once the PN phase is reached.