XZ Tau的三重麻烦：使用Jansky超大阵列进行深度成像
Triple trouble for XZ Tau: deep imaging with the Jansky Very Large Array
摘要：
我们提出了新的观测XZ Tau系统的高角分辨率（55毫角秒）与卡尔G。在2004年用VLA对XZ Tau进行的观测似乎显示了一个三重系统，XZ Tau A被分解为两个源，XZ Tau A和XZ Tau C。XZ Tau A和C的角距（0.09角秒）表明，预计轨道间隔约为13天文单位，可能的轨道周期约为40年。我们的观测是在大约8年后获得的，是这个假定轨道周期的五分之一，因此应该允许我们限制XZ Tau C的轨道，并评估最近一次近星点通过C与XZ Tau A的扩展光学流出相吻合的可能性。尽管与以前的观察结果相比，灵敏度和分辨率有所提高，但我们在数据中没有发现XZ Tau C的证据。探测到的成分A和B的信噪比大于10;它们的轨道与以前的研究一致，尽管XZ Tau A的发射似乎较弱。有三种可能的解释：要么XZ Tau C是凌日XZ Tau A，这与近星通过假说大致一致，要么2004年看到的发射是一个瞬态，或者XZ Tau C不存在。第四种解释是，XZ Tau C是从系统中被抛出的，但由于XZ Tau A和XZ Tau B的轨道缺乏角动量重新分布而被驳回。我们的观测不足以区分其余的可能性，至少在足够晚的时间获得进一步的VLA观测之前是这样。进一步的未检测将允许我们拒绝凌日假说，以及XZ Tau C作为XZ Tau A流出物的代理的近星点通道。
英文摘要：
We present new observations of the XZ Tau system made at high angular resolution (55 milliarcsec) with the Karl G. Jansky Very Large Array (VLA) at a wavelength of 7 mm. Observations of XZ Tau made with the VLA in 2004 appeared to show a triple system, with XZ Tau A resolved into two sources, XZ Tau A and XZ Tau C. The angular separation of XZ Tau A and C (0.09 arcsec) suggested a projected orbital separation of around 13 AU with a possible orbital period of around 40 yr. Our observations were obtained approximately 8 yr later, a fifth of this putative orbital period, and should therefore allow us to constrain the orbit of XZ Tau C, and evaluate the possibility that a recent periastron passage of C coincided with the launch of extended optical outflows from XZ Tau A. Despite improved sensitivity and resolution compared with previous observations, we find no evidence of XZ Tau C in our data. Components A and B are detected with a signal-to-noise ratio greater than ten; their orbits are consistent with previous studies, although the emission from XZ Tau A appears to be weaker. Three possible interpretations are offered: either XZ Tau C is transiting XZ Tau A, which is broadly consistent with the periastron passage hypothesis, or the emission seen in 2004 was that of a transient, or XZ Tau C does not exist. A fourth interpretation, that XZ Tau C was ejected from the system, is dismissed due to the lack of angular momentum redistribution in the orbits of XZ Tau A and XZ Tau B that would result from such an event. Our observations are insufficient to distinguish between the remaining possibilities, at least not until we obtain further VLA observations at a sufficiently later time. A further non-detection would allow us to reject the transit hypothesis, and the periastron passage of XZ Tau C as agent of XZ Tau A's outflows.
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