恒星喷流模拟中辐射结的自行--脉动入流条件的另一种选择
Proper motions of radiative knots in simulations of stellar jets - An alternative to pulsating inflow conditions
摘要：
来自年轻恒星物体的细长喷流通常呈现出结节状结构，由一系列明亮的结形成，这些结具有单独的自行运动。虽然人们普遍认为，内部冲击在这种结构的形成和动力学中起着重要作用，但它们的确切起源和所观察到的自行背后的机制仍然是一个有争议的问题。我们的目标是研究数值的起源，动力学，和排放性能等结。轴对称模拟进行冲击捕获代码的气体动力学，允许分子，原子和电离氢在非平衡浓度电离/复合过程。计算了SII线的辐射损失，并将所得的合成发射图与观测结果进行了比较。我们发现，一种模式的定期间隔的内部斜激波，其特征在于由个人自行车，产生的压力梯度之间的传播射流和时变外部茧。在膨胀不足的情况下，轻射流的排放结被发现与射流下游移动，随着速度的增加和亮度衰减的领先弓激波。这表明，在恒星喷流中观察到的结的基本性质可以复制，即使没有调用特设脉动条件在喷流入口，虽然这两种情况之间的相互作用是肯定可能的。
英文摘要：
Elongated jets from young stellar objects typically present a nodular structure, formed by a chain of bright knots of enhanced emission with individual proper motions. Though it is generally accepted that internal shocks play an important role in the formation and dynamics of such structures, their precise origin and the mechanisms behind the observed proper motions is still a matter of debate. Our goal is to study numerically the origin, dynamics, and emission properties of such knots. Axisymmetric simulations are performed with a shock-capturing code for gas dynamics, allowing for molecular, atomic, and ionized hydrogen in non-equilibrium concentrations subject to ionization/recombination processes. Radiative losses in SII lines are computed, and the resulting synthetic emission maps are compared with observations. We show that a pattern of regularly spaced internal oblique shocks, characterized by individual proper motions, is generated by the pressure gradient between the propagating jet and the time variable external cocoon. In the case of under-expanded, light jets the resulting emission knots are found to move downstream with the jet flow, with increasing velocity and decaying brightness toward the leading bow shock. This suggests that the basic properties of the knots observed in stellar jets can be reproduced even without invoking ad hoc pulsating conditions at the jet inlet, though an interplay between the two scenarios is certainly possible.
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