[论文解读] NIR spectroscopic survey of protostellar jets in the star forming region IC 1396N

F. Massi, López, Rosario+3 more|arXiv (Cornell University)|May 19, 2022

Astrophysics and Star Formation Studies参考文献 42被引用 1

一句话总结

本研究利用TNG望远镜的低分辨率长缝近红外光谱，对IC 1396N星形成区中原恒星喷流内H2转振发射进行了近红外光谱调查。结果证实冲击激发是H2发射的主要机制，揭示了复杂的动力学特征，包括共存的蓝移和红移结核，表明喷流存在进动现象，同时约束了喷流结核的物理条件与消光程度，挑战了A和B丝状结构源自同一中等质量源BIMA 2的假设。

ABSTRACT

Abridged. The bright-rimmed cloud IC1396N hosts CO, H$_2$, and Herbig-Haro outflows powered by millimetre compact sources. We aim to characterise the kinematics and physical conditions of the H$_2$ emission features spread over IC1396N, which appear as chains of knots with a jet-like morphology, tracing different H$_2$ outflows, and to obtain further information about (and an identification of) the driving sources. Low-resolution, long-slit near-infrared spectra were acquired with NICS at the TNG, using grisms KB (R~1200), HK and JH (R~500). Several slit pointings and PA were used throughout IC1396N to sample a number of the H$_2$ knots previously detected in deep H$_2$ 2.12 $\mu$m images. The knots exhibit rich ro-vibrational spectra of H$_2$, consistent with shock-excited excitation, from which radial velocities and relevant physical conditions of the IC1396N H$_2$ outflows were derived. These also allowed estimating extinction ranges towards several features. [FeII] emission was only detected towards a few knots, which also display unusually large H$_2$ 1-0 S(3)/S(1) flux ratios. The obtained radial velocities confirm that most of the outflows are close to the plane of the sky. Nearby knots in the same chain often display different radial velocities, both blue-shifted and red-shifted, which we interpret as due to ubiquitous jet precession in the driving sources or the development of oblique shocks. One of the chains (strand A) appears as a set of features trailing a leading bow-shock structure consistent with the results of 3-D magneto-hydrodynamical models. Either side of the leading bow-shock (A15) exhibits a different radial velocity, whose possible explanations are discussed in the paper. Our data cannot confirm whether strands A and B have both been originated by the intermediate mass young stellar object BIMA 2.

研究动机与目标

• 理解IC 1396N原恒星喷流中H2转振发射的激发机制。
• 表征多个喷流中H2发射结核的动力学与物理条件（温度、消光）。
• 通过径向速度与毫米波连续谱及CO喷流的空间相关性，识别并定位观测到的H2喷流结构的驱动源。
• 评估A和B丝状结构的复杂形态是否可由BIMA 2源驱动的单一进动喷流解释。
• 将观测到的H2动力学与形态与三维磁流体动力学模型进行比较，以评估喷流动力学与激波结构。

提出的方法

• 使用TNG望远镜上的NICS仪器，通过KB（R ~1200）、HK和JH（R ~500）光栅获取低分辨率长缝近红外光谱。
• 在多个位置角上进行空间分辨光谱观测，以采样先前在H2 2.12 µm成像中检测到的H2结核。
• 从H2 1–0 S(1)、S(0)和S(2)跃迁中推导径向速度，通过各线间的一致性验证速度的可靠性。
• 利用H2线比值（如1–0 S(1)/S(0)、1–0 S(1)/S(2)和1–0 S(3)/S(1)）区分冲击激发与紫外荧光激发机制。
• 在局部热动平衡（LTE）假设下，利用所有检测到的H2谱线，同时求解激发温度（Tex）与视觉消光（AV）。
• 将观测到的H2结核形态与径向速度结构与三维磁流体动力学模型进行比较，以评估弓形激波与进动特征。

实验结果

研究问题

• RQ1 IC 1396N结核中H2转振发射的主要激发机制（冲击激发 vs. 紫外荧光激发）是什么？
• RQ2 H2结核的径向速度如何约束喷流相对于天球平面的取向与动力学？
• RQ3 A和B丝状结构的复杂形态与动力学结构是否可由BIMA 2源驱动的单一进动喷流解释？
• RQ4 不同结核链中H2发射气体的物理状态（Tex、AV）如何？其与消光及不同波段线检测的相关性如何？
• RQ5 观测到的A丝状结构前导弓形激波是否与三维MHD模拟的喷流喷流一致？

主要发现

• IC 1396N中H2转振发射主要由冲击激发驱动，H2线比值与冲击激发一致，与紫外荧光激发机制不一致。
• H2结核的径向速度范围为−40至+50 km s−1，同一丝状结构中同时存在蓝移与红移成分，表明大多数喷流接近天球平面，且可能由进动喷流驱动。
• 结核A1–A15表现出前导弓形激波结构（A15），其东侧与西侧具有不同的径向速度，与三维MHD模型预测的进动喷流中弓形激波传播特征一致。
• 丝状结构C的消光较低（AV = 0–2 mag），而A、B和G丝状结构的消光较高（AV = 5–10 mag），这解释了为何C中可检测到J波段H2谱线，而A1–A15与B1–B11中无法检测到。
• 在最消光严重的结核（A1–A15与O1）中检测到较高的H2 1–0 S(3)/S(1)通量比与[Fe ii]发射，表明这些区域可能存在C型激波或复杂激波结构。
• 无论是简单的进动模型，还是涉及BIMA 2附近存在大质量伴星的模型，均无法解释A和B丝状结构的空间与动力学构型，表明其起源更复杂，或存在独立的驱动源。