分子云核心IV中恒星形成的模拟。turbulence的作用和热力学
Simulating star formation in molecular cloud cores IV. The role of turbulence and thermodynamics
摘要：
我们对具有不同初始湍流水平（alpha_turb= 0.05，0.10，0.25）的低质量核的坍缩和碎裂进行了SPH模拟。我们采用了一种新的能量方程处理方法，该方法捕捉了尘埃和气体（包括尘埃升华、分子和H^-离子的影响）引起的冷却辐射相对于不透明度的输运。我们还使用标准正压状态方程进行比较模拟。我们发现，与正压状态方程相比，我们对能量方程的更现实的处理导致更多的原恒星天体形成，以及更高比例的棕矮星;多重性频率基本上没有变化，但多重系统往往具有更短的周期（因子~3），更高的偏心率和更高的质量比。其原因是，小碎片能够更有效地冷却与新的处理，正压状态方程相比。我们发现，破碎的过程往往是双峰。第一个形成的原恒星通常是最大质量的，也就是主恒星。然而，通常盘状结构随后在这个初级周围形成，然后，一旦它积累了足够的质量，就迅速破碎以产生几个次级。我们相信这种盘状结构的延迟碎裂很可能是非常低质量的氢燃烧恒星和褐矮星的重要来源。
英文摘要：
We perform SPH simulations of the collapse and fragmentation of low-mass cores having different initial levels of turbulence (alpha_turb=0.05,0.10,0.25). We use a new treatment of the energy equation which captures the transport of cooling radiation against opacity due to both dust and gas (including the effects of dust sublimation, molecules, and H^- ions). We also perform comparison simulations using a standard barotropic equation of state. We find that -- when compared with the barotropic equation of state -- our more realistic treatment of the energy equation results in more protostellar objects being formed, and a higher proportion of brown dwarfs; the multiplicity frequency is essentially unchanged, but the multiple systems tend to have shorter periods (by a factor ~3), higher eccentricities, and higher mass ratios. The reason for this is that small fragments are able to cool more effectively with the new treatment, as compared with the barotropic equation of state. We find that the process of fragmentation is often bimodal. The first protostar to form is usually, at the end, the most massive, i.e. the primary. However, frequently a disc-like structure subsequently forms round this primary, and then, once it has accumulated sufficient mass, quickly fragments to produce several secondaries. We believe that this delayed fragmentation of a disc-like structure is likely to be an important source of very low-mass hydrogen-burning stars and brown dwarfs.
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