仙王座A中的脉冲旋进喷流
A Pulsed, Precessing Jet in Cepheus A
摘要：
我们目前的近红外H2，无线电CO和热红外观测附近的大质量恒星形成区仙王座A（Cep A）。从沿着四个不同的喷流轴排列的H2弓形激波，我们推断大规模的原恒星源HW 2驱动着一个脉冲式的旋进喷流，在大约104年的时间里，它的方向改变了大约45度。目前的HW 2射电喷流代表了这一系列喷发中最近的事件。这种情况与最近发现的HW 2周围的圆盘相一致，垂直于当前的喷流方向，并且在与圆盘半径相当的投影距离处存在同伴。我们建议，Cep A系统形成的磁盘辅助捕获的兄弟星HW 2。本文给出了一个15 M太阳恒星的数值模型，该恒星有一个拱盘，伴星绕其倾斜的偏心轨道运行。伴星通过或靠近盘的近距离通道会导致增强的吸积和质量损失，以及盘的强制进动和喷流中相关的方向变化。观测揭示了第二个强大的外流，从无线电源HW 3c或HW 3d出现。这股气流与蓝移的CO排放和东边微弱的H2弓形激波以及西边的HH 168有关。来自HW 2和HW 3c/d的气流之间的碰撞可能是导致Cep A West X射线和射电连续谱发射的原因。
英文摘要：
We present near-infrared H2, radio CO, and thermal infrared observations of the nearby massive star-forming region Cepheus A (Cep A). From H2 bow shocks arranged along four distinct jet axes, we infer that the massive protostellar source HW2 drives a pulsed, precessing jet that has changed its orientation by about 45 degrees in roughly 104 years. The current HW2 radio jet represents the most recent event in this time series of eruptions. This scenario is consistent with the recent discovery of a disk around HW2, perpendicular to the current jet orientation, and with the presence of companions at projected distances comparable to the disk radius. We propose that the Cep A system formed by the disk-assisted capture of a sibling star by HW2. We present a numerical model of a 15 M_sun star with a circumstellar disk, orbited by a companion in an inclined, eccentric orbit. Close passages of the companion through or near the disk result in periods of enhanced accretion and mass loss, as well as forced precession of the disk and associated orientation changes in the jet. The observations reveal a second powerful outflow that emerges from radio source HW3c or HW3d. This flow is associated with blueshifted CO emission and a faint H2 bow shock to the east, and with HH 168 to the west. A collision between the flows from HW2 and HW3c/d may be responsible for X-ray and radio continuum emission in Cep A West.
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