Investigating the transport of angular momentum from young stellar objects : do H2 jets from Class I YSOs rotate
Investigating the transport of angular momentum from young stellar objects : do H2 jets from Class I YSOs rotate
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研究年轻恒星的角动量传输：来自 I 类 YSO 的 H2 喷流是否旋转
DOI：
10.1051/0004-6361:20078494
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发表时间：
2008
影响因子：
6.5
通讯作者：
M. Takami
中科院分区：
文献类型：
--
作者：
A. Chrysostomou;F. Bacciotti;B. Nisini;T. Ray;J. Eislöffel;Christopher Davis;M. Takami
目标。在这项初步研究中，我们检查了嵌入的I类源HH 26和HH 72的分子射流，首次搜索了年轻嵌入源的射流旋转的运动学特征。方法。利用VLT/ISAAC获得了H 2 1-0 S(1)跃迁的高分辨率长缝光谱。狭缝与气流方向垂直，距离源约2″。构造了位置-速度（PV）图，并测量了射流横向的强度加权径向速度。结果。HH 26的平均强度加权速度在$v_{\rm LSR} \sim -90$和-65 km s -1之间变化，HH 72的平均强度加权速度在-60和-10 km s -1之间变化；极大值出现在强度峰附近，并向喷流边界方向减弱。HH 26和HH 72的速度色散分别为45和80 km s -1，气体运动速度高达-100 km s -1。两个物体的不对称PV图都可以看到，一个简单的圆柱形射流截面经验模型表明，原则上可以通过射流旋转单独再现。假设磁离心发射，观测到的HH 26流可能起源于距离恒星2-4 AU的圆盘半径，在观测位置磁场的环面分量占主导地位，这与磁准直模型一致。我们估计HH 26射流传递的动能角动量为$2 \times10^{-5}\,M_\odot$ yr -1 AU km s -1。这个值（流传递的总角动量的下限）已经达到70% of the angular momentum that has to be extracted from the disk for the accretion to proceed at the observed rate. Conclusions. These results of this pilot study suggest that jet rotation may also be present at early evolutionary phases and support the hypothesis that they carry away excess angular momentum, thus allowing the central protostar to increase its mass.
Aims. In this pilot study, we examine molecular jets from the embedded Class I sources, HH 26 and HH 72, to search, for the first time, for kinematic signatures of jet rotation from young embedded sources. Methods. High-resolution long-slit spectroscopy of the H 2 1-0 S(1) transition was obtained using VLT/ISAAC. The slit was placed perpendicular to the flow direction about 2″ from the sources. Position-velocity (PV) diagrams are constructed and intensity-weighted radial velocities transverse to the jet flow are measured. Results. Mean intensity-weighted velocities vary between $v_{\rm LSR} \sim -90$ and -65 km s -1 for HH 26, and -60 and -10 km s -1 for HH 72; maxima occur close to the intensity peak and decrease toward the jet borders. Velocity dispersions are ~45 and ~80 km s -1 for HH 26 and HH 72, respectively, with gas motions as fast as -100 km s -1 present. Asymmetric PV diagrams are seen for both objects, which a simple empirical model of a cylindrical jet section shows could in principle be reproduced by jet rotation alone. Assuming magneto-centrifugal launching, the observed HH 26 flow may originate at a disk radius of 2-4 AU from the star with the toroidal component of the magnetic field dominant at the observed location, in agreement with magnetic collimation models. We estimate that the kinetic angular momentum transported by the HH 26 jet is ~$2 \times10^{-5}\,M_\odot$ yr -1 AU km s -1 . This value (a lower limit to the total angular momentum transported by the flow) already amounts to 70% of the angular momentum that has to be extracted from the disk for the accretion to proceed at the observed rate. Conclusions. These results of this pilot study suggest that jet rotation may also be present at early evolutionary phases and support the hypothesis that they carry away excess angular momentum, thus allowing the central protostar to increase its mass.