Evolution of First Cores in Rotating Molecular Cores
Evolution of First Cores in Rotating Molecular Cores
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DOI：
10.1086/504028
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发表时间：
2006-07
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影响因子：
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通讯作者：
K. Saigo;K. Tomisaka
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作者：
K. Saigo;K. Tomisaka
我们使用轴对称数值计算定量研究旋转对恒星形成过程的影响。在中心区域变得光学变厚并在质量吸积的驱动下继续收缩之后，绝热流体静力物体（所谓的第一核心）在收缩的云核心中形成。旋转的第一核心的结构以其总角动量 Jcore 和质量 Mcore 为特征，两者都随着时间的推移而增加。我们发现第一个核心以恒定的 Jcore/M 演化。第一个核心的进化路径可以分为两种类型。在 Jcore/M 0.015G/(ciso) 的缓慢旋转核心中，在中心密度达到 H2 解离密度之前停止其收缩，并且不会开始第二次塌陷。这些快速旋转的第一核心遭受非轴对称不稳定性的影响，例如形成巨大的旋臂、变形为条形或碎裂。尽管旋转的第一核心具有较小的平均光度 Lcore = 0.003-0.03 L☉，假设核心质量吸积率恒定。它们的寿命持续数千年或更长时间，比非旋转云的预期寿命（约 1000 年）要长得多。我们预计至少有百分之几的前恒星核心包含作为光度非常低的物体的第一核心。此外，我们发现 0.012G/(ciso) < Jcore/M < 0.015G/(ciso) 的核心可能会形成紧密的双星系统，在第二次塌陷阶段后初始分离为 0.02-0.1 AU。
We investigate the effect of rotation on the star formation process quantitatively using axisymmetric numerical calculations. An adiabatic hydrostatic object (the so-called first core) forms in a contracting cloud core, after the central region becomes optically thick and continues to contract, driven by mass accretion onto it. The structure of a rotating first core is characterized by its total angular momentum Jcore and mass Mcore, both of which increase by accretion with time. We find that the first core evolves with a constant Jcore/M. Evolutionary paths of first cores can be classified into two types. In a slowly rotating core with Jcore/M 0.015G/(ciso) stops its contraction before the central density reaches the H2 dissociation density and does not begin the second collapse. These rapidly rotating first cores suffer from nonaxisymmetric instabilities, such as formation of massive spiral arms, deformation into a bar, or fragmentation. Although the rotating first cores have small average luminosities of Lcore = 0.003-0.03 L☉, assuming a constant mass accretion rate core. Their lifetimes last several thousand years or more, which is much longer than those expected for nonrotating clouds (~1000 yr). We expect that at least several percent of prestellar cores contain first cores as very low luminosity objects. Furthermore, we find a core with 0.012G/(ciso) < Jcore/M < 0.015G/(ciso) may form close binary systems with initial separation of 0.02-0.1 AU after the second collapse phase.