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arXiv 1612.02016astro-ph.SR
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非理想磁流体动力学对双星形成的影响

The impact of non-ideal magnetohydrodynamics on binary star formation

James Wurster, Daniel J. Price, Matthew R. Bate

备注：
Accepted to MNRAS. 18 pages, 20 figures, 1 appendix
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摘要：

利用三维光滑粒子磁流体动力学模拟方法研究了非理想磁流体动力学（MHD）对双星形成的影响，模拟了一个太阳质量的旋转扰动分子云核的引力坍缩过程.除了欧姆电阻率，双极扩散和霍尔效应的作用，我们还研究了磁场强度，取向和密度扰动的幅度的影响。在模拟次临界核时，理想MHD模型不会坍缩，而非理想MHD模型坍缩形成单个原恒星。在超临界理想MHD模型中，增大磁场强度或减小初始密度扰动幅度均会减小初始二元分离。最初垂直于旋转轴的强磁场抑制双星的形成，并产生比磁场最初与旋转轴对齐时强约10倍的磁场盘。当包含非理想磁流体动力学时，所产生的圆盘更大，质量更大，并且在更宽的轨道上形成双星。由非理想MHD效应引起的超临界核中的微小差异被近星点附近的双星相互作用放大。总体而言，非理想效应对双星形成和早期演化的影响很小，初始条件起主导作用。

英文摘要：

We investigate the effect of non-ideal magnetohydrodynamics (MHD) on the formation of binary stars using a suite of three-dimensional smoothed particle magnetohydrodynamics simulations of the gravitational collapse of one solar mass, rotating, perturbed molecular cloud cores. Alongside the role of Ohmic resistivity, ambipolar diffusion and the Hall effect, we also examine the effects of magnetic field strength, orientation and amplitude of the density perturbation. When modelling sub-critical cores, ideal MHD models do not collapse whereas non-ideal MHD models collapse to form single protostars. In super-critical ideal MHD models, increasing the magnetic field strength or decreasing the initial density perturbation amplitude decreases the initial binary separation. Strong magnetic fields initially perpendicular to the rotation axis suppress the formation of binaries and yield discs with magnetic fields ~10 times stronger than if the magnetic field was initially aligned with the rotation axis. When non-ideal MHD is included, the resulting discs are larger and more massive, and the binary forms on a wider orbit. Small differences in the super-critical cores caused by non-ideal MHD effects are amplified by the binary interaction near periastron. Overall, the non-ideal effects have only a small impact on binary formation and early evolution, with the initial conditions playing the dominant role.

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