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arXiv 1701.04243astro-ph.GAastro-ph.SR
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Herschel观测到的BHR71外流的冲击气体：原子喷流的间接证据

The shocked gas of the BHR71 outflow observed by Herschel: indirect evidence for an atomic jet

M. Benedettini, A. Gusdorf, B. Nisini, B. Lefloch, S. Anderl, G. Busquet, C. Ceccarelli, C. Codella, S. Leurini, L. Podio

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16 pages, 15 figures
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摘要：

在BHR 71区域，两颗低质量的原恒星驱动着两个可区分的外流。它们构成了研究冲击化学效应及其形成机制的理想实验室。我们的目标是定义BHR 71流出的暖气体成分的形态，并对其冲击成分进行建模。我们首次在CO（14-13）、H $_2$ O（2 $_{21}$ -1 $_{10}$）、H $_2$ O（2 $_{12}$ -1 $_{01}$）和[OI] 145 $μ$ m线中获得了BHR 71外流的远红外赫歇尔图像，揭示了与快速外流气体相关的几个温暖、冲击气体结的存在。在其中两个节点中，我们通过比较从几个分子到激波模型网格的大量跃迁，对物理条件进行了详细的研究。流出结中的赫歇尔线比率非常相似，表明快速移动气体的激发条件在流出的第一个$\sim$ 0.068 pc内没有显著变化，除了在分子云外扩展的南部蓝移叶的末端。结A中CO谱线的旋转图、谱线轮廓和LVG分析表明存在两种气体组分：一个延伸的，冷的（$T\sim$ 80 K）和致密（$n$（H $_2$）= 3 $\times$ 10 $^5$ -4 $\times$ 10 $^6$ cm $^{-3}$）和另一紧凑型（18弧秒），温暖（$T$ = 1700-2200 K），密度稍低（$n$（H $_2$）=（2-6）$\times$ 10 $^4$ cm $^{-3}$）。在两个最亮的节点（在那里我们进行了冲击模拟），我们发现，H $_2$和CO是很好的拟合与非平稳（年轻）的冲击。然而，这些模型大大低估了观测到的[OI]和OH线的通量，但与H $_2$ O的通量相差不太远，这就需要一个额外的、可能是离解的J型激波分量。我们的模拟间接地表明，一个额外的冲击分量存在，可能是残留的主要射流

英文摘要：

In the BHR71 region, two low-mass protostars drive two distinguishable outflows. They constitute an ideal laboratory to investigate the effects of shock chemistry and the mechanisms that led to their formation. We aim to define the morphology of the warm gas component of the BHR 71 outflow and at modelling its shocked component. We present the first far infrared Herschel images of the BHR71 outflow in the CO(14-13), H$_2$O (2$_{21}$-1$_{10}$), H$_2$O (2$_{12}$-1$_{01}$) and [OI] 145 $μ$m, lines, revealing the presence of several knots of warm, shocked gas associated with fast outflowing gas. In two of these knots we performed a detailed study of the physical conditions by comparing a large set of transitions from several molecules to a grid of shock models. Herschel lines ratios in the outflow knots are quite similar, showing that the excitation conditions of the fast moving gas do not change significantly within the first $\sim$ 0.068 pc of the outflow, apart at the extremity of the southern blue-shifted lobe that is expanding outside the molecular cloud. Rotational diagram, spectral line profile and LVG analysis of the CO lines in knot A show the presence of two gas components: one extended, cold ($T\sim$80 K) and dense ($n$(H$_2$) = 3$\times$10$^5$-4$\times$10$^6$ cm$^{-3}$) and another compact (18 arcsec), warm ($T$ = 1700-2200 K) with slightly lower density ($n$(H$_2$) = (2-6)$\times$10$^4$ cm$^{-3}$). In the two brightest knots (where we performed shock modelling) we found that H$_2$ and CO are well fitted with non-stationary (young) shocks. These models, however, significantly underestimate the observed fluxes of [OI] and OH lines, but are not too far off those of H$_2$O, calling for an additional, possibly dissociative, J-type shock component. Our modelling indirectly suggests that an additional shock component exists, possibly a remnant of the primary jet

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