由VLBA观测揭示的喷泉IRAS 18286-0959的高速旋进喷流
High Velocity Precessing Jets from the Water Fountain IRAS 18286-0959 Revealed by VLBA Observations
摘要：
本文报道了与“喷泉”IRAS 18286-0959有关的22.2GHz水脉泽辐射的多历元VLBA观测结果。我们认为，该天体是水脉泽辐射追踪的第二个高度准直双极旋进外流的例子，另一个是W 43 A。探测到的水排放峰值分布在-50 ~150 km/s的速度范围内。发现70%以上的脉泽特征的空间分布是沿着一个从东南向西北延伸的螺旋喷流（喷流1）高度准直的，其余的特征似乎跟踪另一个具有不同方向的螺旋喷流（喷流2）。这两股喷流形成了一个“双螺旋”模式，跨越约200毫弧秒。用双极旋进喷流模型对脉泽分布进行了合理的拟合。计算得到喷流1和喷流2的三维速度分别为138 km/s和99 km/s。喷流1的岁差周期约为56年。对于射流2，测试了三种可能的模型，它们给出了运动学参数的不同值。我们建议，两个喷流的外观是一个单一的驱动源与显着的自行的结果。
英文摘要：
We report the results of multi-epoch VLBA observations of the 22.2GHz water maser emission associated with the "water fountain" IRAS 18286-0959. We suggest that this object is the second example of a highly collimated bipolar precessing outflow traced by water maser emission, the other is W43A. The detected water emission peaks are distributed over a velocity range from -50km/s to 150km/s. The spatial distribution of over 70% of the identified maser features is found to be highly collimated along a spiral jet (jet 1) extended southeast to northwest, the remaining features appear to trace another spiral jet (jet 2) with a different orientation. The two jets form a "double-helix" pattern which lies across ~200 milliarcseconds. The maser distribution is reasonably fit by a model consisting of two bipolar precessing jets. The 3D velocities of jet 1 and jet 2 are derived to be 138km/s and 99km/s, respectively. The precession period of jet 1 is about 56 years. For jet 2, three possible models are tested and they give different values for the kinematic parameters. We propose that the appearance of two jets is the result of a single driving source with significant proper motion.
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