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arXiv 0908.1285astro-ph.SRastro-ph.EP
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金牛T星和褐矮星吸积的双峰性

The Bimodality of Accretion In T Tauri Stars and Brown Dwarfs

E. I. Vorobyov, Shantanu Basu

备注：
Accepted for publication in ApJ
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摘要：

我们提出的数值解的星前核心的崩溃，导致形成和演化的拱星盘。然后，对圆盘的演化进行了长达300万年的跟踪。不同初始质量和自转速率的各种模型使我们能够研究褐矮星和低质量金牛座T星周围的吸积盘，中心天体质量为$M_st < 0.2 Msun$，以及中等和高质量金牛座T星（0.2 Msun <Mst < 3.0 Msun）。我们的模型包括自引力，并允许非轴对称运动。除了自洽产生的引力矩外，我们还引入了一个有效的湍流α-粘性，α= 0.01，这使得我们能够特别地模拟低质量区域中的吸积，在该区域中，盘的自引力逐渐减小。一系列的模型与观测动机值的初始比率的旋转引力能产生的相关性之间的质量吸积率\dot{M}和M_st是相对陡峭的，如观察到的。此外，我们的建模揭示了\dot{M} -M_st相关性双峰的证据，在较低的质量和较浅的斜率在中间和上部的群众，也暗示了观察。我们发现，忽略磁盘的自引力导致一个陡峭得多的\dot{M} -M_st关系的中，高质量的金牛座T星。这表明，一个准确的处理全球自引力是必不可少的了解观测的拱星盘。

英文摘要：

We present numerical solutions of the collapse of prestellar cores that lead to the formation and evolution of circumstellar disks. The disk evolution is then followed for up to three million years. A variety of models of different initial masses and rotation rates allows us to study disk accretion around brown dwarfs and low-mass T Tauri stars, with central object mass $M_st < 0.2 Msun$, as well as intermediate and upper-mass T Tauri stars (0.2 Msun < M_st < 3.0 Msun). Our models include self-gravity and allow for nonaxisymmetric motions. In addition to the self-consistently generated gravitational torques, we introduce an effective turbulent α-viscosity with α= 0.01, which allows us particularly to model accretion in the low-mass regime where disk self-gravity is diminishing. A range of models with observationally-motivated values of the initial ratio of rotational to gravitational energy yields a correlation between mass accretion rate \dot{M} and M_st that is relatively steep, as observed. Additionally, our modeling reveals evidence for a bimodality in the \dot{M}--M_st correlation, with a steeper slope at lower masses and a shallower slope at intermediate and upper masses, as also implied by observations. We show that the neglect of disk self-gravity leads to a much steeper \dot{M}--M_st relation for intermediate and upper-mass T Tauri stars. This demonstrates that an accurate treatment of global self-gravity is essential to understanding observations of circumstellar disks.

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