VARIABLE PROTOSTELLAR ACCRETION WITH EPISODIC BURSTS
VARIABLE PROTOSTELLAR ACCRETION WITH EPISODIC BURSTS
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DOI：
10.1088/0004-637x/805/2/115
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
E. Vorobyov;S. Basu
中科院分区：
文献类型：
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作者：
E. Vorobyov;S. Basu
我们介绍了盘引力不稳定性和碎裂模型的最新发展，该模型最初是由我们引入的，用于解释恒星形成早期阶段的幕式吸积爆发。利用我们改进的盘热平衡和星-盘相互作用的数值流体力学模型，我们计算了由前恒星核引力崩塌形成的原星盘的演化。与我们以前的研究结果一致，我们发现初始质量和角动量较大的核产生的盘更有利于引力不稳定性和碎裂，而较高的本底辐照和磁场则缓和了盘的碎裂倾向。在我们的模型中，原恒星的吸积是时变的，这要归功于引力不稳定盘中不同螺旋模式之间的非线性相互作用，并且当碎片迁移到恒星上时，由于与其他碎片或螺旋臂的引力相互作用，原恒星的吸积可能会经历周期性的爆发。大多数爆发发生在部分嵌入的I类阶段，一小部分发生在深度嵌入的0类阶段，少数可能发生在光学可见的II类阶段。平均爆发持续时间和平均光度与FUors的观测结果符合得很好。该模型预测了两种类型的爆发的存在：一种是孤立的，显示出清晰的发光度峰，间隔着较长的静止吸积周期(∼104？>；yr)；另一种是簇状的，展示了在短短几百年内相继发生的几次爆发。最后，我们估计40%-70%的恒星形成核可以在形成星盘系统后出现爆发。
We present the latest development of the disk gravitational instability and fragmentation model, originally introduced by us to explain episodic accretion bursts in the early stages of star formation. Using our numerical hydrodynamics model with improved disk thermal balance and star-disk interaction, we computed the evolution of protostellar disks formed from the gravitational collapse of prestellar cores. In agreement with our previous studies, we find that cores of higher initial mass and angular momentum produce disks that are more favorable to gravitational instability and fragmentation, while a higher background irradiation and magnetic fields moderate the disk tendency to fragment. The protostellar accretion in our models is time-variable, thanks to the nonlinear interaction between different spiral modes in the gravitationally unstable disk, and can undergo episodic bursts when fragments migrate onto the star owing to the gravitational interaction with other fragments or spiral arms. Most bursts occur in the partly embedded Class I phase, with a smaller fraction taking place in the deeply embedded Class 0 phase and a few possible bursts in the optically visible Class II phase. The average burst duration and mean luminosity are found to be in good agreement with those inferred from observations of FUors. The model predicts the existence of two types of bursts: the isolated ones, showing well-defined luminosity peaks separated with prolonged periods ( ∼ 10 4 ?> yr) of quiescent accretion, and clustered ones, demonstrating several bursts occurring one after another during just a few hundred years. Finally, we estimate that 40%–70% of the star-forming cores can display bursts after forming a star-disk system.