HH212中SiO微喷流的PdBI亚弧秒研究--0级喷流的起源和准直
PdBI sub-arcsecond study of the SiO microjet in HH212 - Origin and collimation of Class 0 jets
摘要：
双极HH 212流出已被映射在SiO使用的高原德布尔干涉仪（PdBI）的扩展配置，揭示了一个高度准直的SiO射流密切相关的H2射流组件。我们研究前所未有的分辨率（0.34”跨喷流轴）的属性的最里面的SiO“”microjet“在1000 AU的这个年轻的0级源，比较它与原子microjet从更先进的来源，并限制其起源。利用SiO通道图研究了微射流的准直性和速度结构。对来自PdBI和亚毫米阵列的SiO（2-1）、（5-4）和（8-7）数据应用大速度梯度分析以限制SiO不透明度和丰度。HH 212 0级微射流在准直和能量预算方面与金牛座T源的原子微射流有惊人的相似之处。此外，SiO线在光学上看起来很厚，不像通常假设的那样。当n（H_2）= 10（7）-10（5）cm（-3）时，SiO/H_2的丰度大于4 × 10（-8）-6 × 10（-5），即占元素硅的0.05-90%。这种相似的喷流宽度，无论是否存在致密的包层，都明确排除了由外部压力引起的喷流准直，并在恒星形成的所有阶段都有利于共同的MHD自准直（可能还有加速）过程。我们建议，更丰富的SiO在0类射流可能主要是由于快速（小于25年）在高射流密度的分子合成。
英文摘要：
The bipolar HH 212 outflow has been mapped in SiO using the extended configuration of the Plateau de Bure Interferometer (PdBI), revealing a highly collimated SiO jet closely associated with the H2 jet component. We study at unprecedented resolution (0.34" across the jet axis) the properties of the innermost SiO ``microjet'' within 1000 AU of this young Class 0 source, to compare it with atomic microjets from more evolved sources and to constrain its origin. The SiO channel maps are used to investigate the microjet collimation and velocity structure. A large velocity gradient analysis is applied to SiO (2-1), (5-4) and (8-7) data from the PdBI and the Submillimeter Array to constrain the SiO opacity and abundance. The HH212 Class 0 microjet shows striking similarities in collimation and energetic budget with atomic microjets from T Tauri sources. Furthermore, the SiO lines appear optically thick, unlike what is generally assumed. We infer T(kin) ~ 50-500 K and an SiO/H2 abundance greater than 4 10(-8)-6 10(-5) for n(H2) = 10(7)-10(5) cm(-3), i.e. 0.05-90% of the elemental silicon. This similar jet width, regardless of the presence of a dense envelope, definitely rules out jet collimation by external pressure, and favors a common MHD self-collimation (and possibly acceleration) process at all stages of star formation. We propose that the more abundant SiO in Class 0 jets could mainly result from rapid (less than 25 yrs) molecular synthesis at high jet densities.
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