FS Tau B is one of the few T Tauri stars that possess a jet and a counterjet as well as an optically visible cavity wall. We obtained images and spectra of its jet-cavity system in the near-infrared H and K bands using the Subaru/Infrared Camera and Spectrograph and detected the jet and the counterjet in the [Fe?II] 1.644 μm line for the first time. Within 2'' the blueshifted jet is brighter, whereas beyond ~5'' the redshifted counterjet dominates the [Fe?II] emission. The innermost blueshifted knot is spectrally resolved to have a large line width of ~110?km?s–1, while the innermost redshifted knot appears spectrally unresolved. The velocity ratio of the jet to the counterjet is ~1.34, which suggests that FS Tau B is driving an asymmetric jet, similar to those found in several T Tauri stars. Combining with optical observations in the literature, we showed that the blueshifted jet has a lower density and higher excitation than the redshifted counterjet. We suggest that the asymmetry in brightness and velocity is the manifestation of a bipolar outflow driving at different mass-loss rates, while maintaining balance of linear momentum. A full explanation of the asymmetry in the FS Tau B system awaits detail modeling and further investigation of the kinematic structure of the wind-associated cavity walls.
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机译：FS Tau B是为数不多的T Tauri恒星之一，它们具有射流和反射流以及光学可见的腔壁。我们使用斯巴鲁/红外相机和光谱仪获得了其近红外H和K波段的射流腔系统的图像和光谱，并首次在[Fe？II] 1.644μm线中检测到射流和反向射流。在2英寸以内，蓝移的射流更亮，而在〜5英寸以内，红移的反向射流占[Fe？II]发射的主导。光谱解析最里面的蓝移结具有大约110？km？s–1的大线宽，而光谱最里面的红移结似乎在光谱上未解析。射流与反射流的速度比约为1.34，这表明FS Tau B正在驱动不对称射流，类似于在几颗T Tauri星中发现的那些。结合文献中的光学观察结果，我们表明蓝移射流比红移反向射流具有更低的密度和更高的激发。我们建议亮度和速度的不对称性是在不同质量损失速率下驱动双极性流出的表现，同时保持了线性动量的平衡。 FS Tau B系统中不对称性的完整解释有待详细建模以及与风相关的腔壁的运动学结构的进一步研究。
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