SiS in Orion-KL: evidence for "outflow" chemistry.
SiS in Orion-KL: evidence for "outflow" chemistry.
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Orion-KL 中的 SiS：“流出”化学的证据。
DOI：
10.1086/165914
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发表时间：
1988
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：
L. Ziurys
通过91 GHz和109 GHz的J = 6-5和J = 5-4旋转跃迁，最终探测到猎户座- kl的si。谱线显示，该物种在LSR速度为7.5 km s-1时存在，在零功率时半宽为36 km s-1。这些特征将si与以IRc2为中心的中速流出（V约为18 km s-1）联系起来，并在热SiO、NH3“平台”、OH、H2O和SiO微波激射器中观测到。该区域si的柱密度估计为Ntot = 4 × 10(15) cm-2，对应于f的分数丰度约为4 × 10（-9）。这样的丰度意味着流出物质的SiO/SiS比约为60，非常接近宇宙O/S比约为40，与离子分子模型预测的SiO/SiS值>约为10(3)形成对比。这种差异可能是由于流出物中存在的高温和高密度，这有利于热平衡丰度类似于在晚型恒星的星周壳中观察到的丰度，而不是“离子分子”型浓度。除了si外，还在91 GHz和109 GHz附近发现了20条新的未识别谱线，以及由HC5N、HC13CCN、HCC13CN、O13CS以及可能的CH3CH2OH、CH3CHO和CH3OD引起的跃迁。
SiS has been conclusively detected toward Orion-KL via its J = 6-5 and J = 5-4 rotational transitions at 91 and 109 GHz. Line profiles indicate that the species is present at an LSR velocity of 7.5 km s-1 with a half-width at zero power of 36 km s-1. Such characteristics associate SiS with the moderate velocity outflow (V approximately 18 km s-1) centered on IRc2 and observed in thermal SiO, the NH3 "plateau," and OH, H2O, and SiO masers. The column density estimated for SiS in this region is Ntot = 4 x 10(15) cm-2, corresponding to a fractional abundance of f approximately 4 x 10(-9). Such an abundance implies an SiO/SiS ratio of approximately 60 in the outflow material, remarkably close to the cosmic O/S ratio of approximately 40 and contrasting with the SiO/SiS value of > approximately 10(3) predicted by ion-molecule models. This difference is probably a result of the high temperatures and densities present in the outflow, which favor thermal equilibrium abundances similar to those observed in the circumstellar shells of late-type stars rather than "ion-molecule"-type concentrations. In addition to SiS, some twenty new unidentified lines near 91 and 109 GHz were detected toward KL, as well as transitions arising from HC5N, HC13CCN, HCC13CN, O13CS, and, possibly, CH3CH2OH, CH3CHO, and CH3OD.