分子云核的坍缩和碎裂。X.扁长铁心的磁制动
Collapse and Fragmentation of Molecular Cloud Cores. X. Magnetic Braking of Prolate and Oblate Cores
摘要：
最初的扁长和扁圆，磁性分子云的崩溃和破碎计算在三维重力，辐射流体动力学代码。该代码包括磁场的影响，在一个近似的方式：磁压力，张力，制动，和双极扩散都建模。对于最初的扁长云和扁圆云，变化的参数是径向密度分布的中心集中的初始程度、初始角速度和磁制动的效率（由因子$f_{mb} = 10^{-4}$或$10^{-3}$表示）。扁圆形的核心都坍缩形成环，可能容易分裂成多个系统。扁长核坍缩的结果很大程度上取决于初始密度分布。中心密度比边界密度高20倍的长形核心坍缩并分裂成双星或四星系统，而中心密度比边界密度高100倍的核心坍缩形成嵌入棒中的单个原恒星。在后一组模型中，磁制动的加入能够抑制原恒星的碎裂，因为当计算没有磁制动的相同模型时（Boss 2002），这些核心碎裂成双星原恒星。这些模型证明了在原恒星坍缩和碎裂研究中纳入磁场的重要性，并表明即使纳入磁场，碎裂成二元和多个系统仍然是原恒星坍缩的可能结果。
英文摘要：
The collapse and fragmentation of initially prolate and oblate, magnetic molecular clouds is calculated in three dimensions with a gravitational, radiative hydrodynamics code. The code includes magnetic field effects in an approximate manner: magnetic pressure, tension, braking, and ambipolar diffusion are all modelled. The parameters varied for both the initially prolate and oblate clouds are the initial degree of central concentration of the radial density profile, the initial angular velocity, and the efficiency of magnetic braking (represented by a factor $f_{mb} = 10^{-4}$ or $10^{-3}$). The oblate cores all collapse to form rings that might be susceptible to fragmentation into multiple systems. The outcome of the collapse of the prolate cores depends strongly on the initial density profile. Prolate cores with central densities 20 times higher than their boundary densities collapse and fragment into binary or quadruple systems, whereas cores with central densities 100 times higher collapse to form single protostars embedded in bars. The inclusion of magnetic braking is able to stifle protostellar fragmentation in the latter set of models, as when identical models were calculated without magnetic braking (Boss 2002), those cores fragmented into binary protostars. These models demonstrate the importance of including magnetic fields in studies of protostellar collapse and fragmentation, and suggest that even when magnetic fields are included, fragmentation into binary and multiple systems remains as a possible outcome of protostellar collapse.
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