暗云L1517中非线性致密核的形成
Non-linear dense core formation in the dark cloud L1517
摘要：
我们提出了一个解决方案，在金牛座L1517暗云中观察到的核心碎片的细丝，以前无法解释（Hacar等。al 2011）。核心碎裂是恒星形成的关键步骤。观测结果表明，这与云气的结构有关，但仍不清楚是哪个过程造成的。我们表明，重力不稳定性过程的等温柱可以解释所表现出的破碎的假设下，扰动增长的主波长。我们使用数值模拟的代码RAMSES，估计观测到的列密度和视线速度，并将它们与观测结果进行比较。观察到的碎片化的一个关键因素是，核心通过在细丝内重新分配质量而生长，因此核心之间的密度在碎片化过程中降低。这通常导致错误的主波长估计，因为它强烈依赖于初始中心密度。我们认为，非线性效应也发挥了重要作用的演变的碎片。一旦密度扰动增长到临界线质量以上，非线性导致与分析预测相比中心核密度的增强。选择正确的初始条件，扰动强度约为20%，导致倾斜校正的视线速度和中心核心密度在观测测量误差内，在一个现实的演变时间。
英文摘要：
We present a solution for the observed core fragmentation of filaments in the Taurus L1517 dark cloud which previously could not be explained (Hacar et. al 2011). Core fragmentation is a vital step for the formation of stars. Observations suggest a connection to the filamentary structure of the cloud gas but it remains unclear which process is responsible. We show that the gravitational instability process of an isothermal cylinder can account for the exhibited fragmentation under the assumption that the perturbation grows on the dominant wavelength. We use numerical simulations with the code RAMSES, estimate observed column densities and line-of-sight velocities and compare them to the observations. A critical factor for the observed fragmentation is that cores grow by redistributing mass within the filament and thus the density between the cores decreases over the fragmentation process. This often leads to wrong dominant wavelength estimates as it is strongly dependent on the initial central density. We argue that non-linear effects also play an important role on the evolution of the fragmentation. Once the density perturbation grows above the critical line-mass, non-linearity leads to an enhancement of the central core density in comparison to the analytical prediction. Choosing the correct initial conditions with perturbation strengths of around 20\%, leads to inclination corrected line-of-sight velocities and central core densities within the observational measurement error in a realistic evolution time.
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