Molecular Abundances and Low-Mass Star Formation. II. Organic and Deuterated Species toward IRAS 16293-2422
Molecular Abundances and Low-Mass Star Formation. II. Organic and Deuterated Species toward IRAS 16293-2422
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DOI：
10.1086/175915
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发表时间：
1995-07
期刊：
影响因子：
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通讯作者：
Ewine;-F.;Van Dishoeck;L. Geoffrey;-A.;Blake;David J. Jansen;T. Groesbeck
中科院分区：
文献类型：
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作者：
Ewine;-F.;Van Dishoeck;L. Geoffrey;-A.;Blake;David J. Jansen;T. Groesbeck
给出了原双星源IRAS 16293-2422在230 GHz和345 GHz波段的毫米线和亚毫米线巡天结果。共检测到44个分子及其同位素体（24种不同的化学物质）的265个系。这里考虑了有机分子和氘化分子的数据；先前的一篇论文（Blake et al. 1994）讨论了含硅和含硫物种的结果。观测结果已通过旋转图和完全统计平衡/辐射传递计算的组合进行了分析。在20英寸（3000 AU）的光束中，至少可以区分出三种物理和化学上不同的成分。第一个组分是由SiO和SO_2等含Si和s分子采集的温暖（T_(kin)≥80k）和致密[^n(H_2)≥(0.5-1)× 10^7 cm^(-3)]气体。这种气体被发现含有丰富的有机分子，如CH_3OH、CH_3CN和H_2CO。它只有3英寸-10英寸大小（500-1500天文单位），很可能代表双极流出物与环双星包壳的相互作用。第二个组成部分是环双星包膜本身，其T_(kin) 40 K和n(H_2) 10^6-10^7 cm^(-3)，尺寸为10“-15”（2000 AU）。它含有常见的分子，如CS、HCO^+和H_2CO。第三部分是较冷、密度较低的外层包络层，它逐渐淡出周围的云核[T_(kin)≥10- 20k]；n(h2)≈(3 × 10^4)-(2 × 10^5) cm^(-3)]。CN、C_2H和C_3H_2等自由基似乎主要存在于这一区域。通过HCN、HCO^+和H^2CO等分子的谱线的自吸收特征也可以探测到周围云物质。我们给出了20”尺度上的束平均丰度，并将其与冷黑云（如L134N和TMC-1）和大质量恒星形成核心（如猎户座- kl）中观测到的束平均丰度进行了比较。发现了非常高的氘分馏比，这更具有热核心区域的特征，而不是寒冷，静止的云。总的来说，在低质量的年轻恒星IRAS 16293-2422中可以区分出的化学和物理制度在质量上与在高质量恒星形成区域中发现的相似，证实了早期的结论，即化学成分更多地取决于物体的年龄而不是质量。
Millimeter and submillimeter line surveys of the protobinary source IRAS 16293-2422 are presented in the 230 and 345 GHz windows. In total, 265 lines belonging to 44 molecules and their isotopomers (24 chemically different species) have been detected. Here the data for organic and deuterated molecules are considered; the results for Si- and S-bearing species have been discussed in an earlier paper (Blake et al. 1994). The observations have been analyzed through a combination of rotation diagrams and full statistical equilibrium/ radiative transfer calculations. At least three physically and chemically different components can be distinguished within the 20" (3000 AU) beam. The first component is the warm (T_(kin) ≳ 80 K) and dense [^n(H_2) ≍ (0.5-1) × 10^7 cm^(-3)] gas sampled by Si- and S-containing molecules such as SiO and SO_2. This gas is found to be rich in organic molecules such as CH_3OH, CH_3CN, and H_2CO, as well. It is only 3"-10" in size (500-1500 AU) and most likely represents the interaction of the bipolar outflow(s) with the circumbinary envelope. The second component is the circumbinary envelope itself, which has T_(kin) 40 K and n(H_2) 10^6-10^7 cm^(-3) and is 10"-15" in size (2000 AU). It contains common molecules like CS, HCO^+, and H_2CO. The third component is the colder, lower density outer part of the envelope, which gradually fades into the ambient surrounding cloud core [T_(kin) ≍ 10-20 K; n(H_2)≈(3 × 10^4)-(2 × 10^5) cm^(-3)]. Radicals such as CN, C_2H, and C_3H_2 appear to reside principally in this region. The ambient cloud material is also probed through self-absorbed features in the line profiles of molecules such as HCN, HCO^+, and H^2CO. Beam-averaged abundances over a 20" scale are presented and are compared with those observed in cold dark clouds such as L134N and TMC-1 and with high-mass star-forming cores such as Orion-KL. Remarkably high deuterium fractionation ratios are found, which are more characteristic of hot core regions than of cold, quiescent clouds. As a whole, the chemical and physical regimes that can be distinguished in the low-mass young stellar object IRAS 16293-2422 are qualitatively similar to those found in high-mass star-forming regions, confirming the earlier conclusion that the chemical composition depends more on the age of the object than its mass.