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arXiv 0910.2686astro-ph.SR
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金牛座T星吸积驱动的日冕加热和星风加速的测试模型

Testing Models of Accretion-driven Coronal Heating and Stellar Wind Acceleration for T Tauri Stars

Steven R. Cranmer

摘要:

经典的金牛T型星是主序前的天体,同时经历吸积、风外流和日冕X射线发射。来自磁层吸积流的等离子体对恒星表面的影响可能是这些恒星上层大气中能量和动量的主要来源。本文提出了一套模型的动力学和加热的三个不同的地区的金牛座T星的吸积影响:(1)直接下方的磁层吸积流的冲击等离子体,(2)恒星风,加速沿开放的磁通量管,(3)封闭的磁回路,类似于太阳的日冕活动区。对于环,日冕加热的自洽模型来自太阳场线缠结和湍流耗散的数值模拟。对金牛座-御夫座恒星形成区的14颗观测良好的恒星的性质建立了独立的模型。平均而言,风质量损失率的预测略低于观测值,这表明盘风或X风也可能有助于测量的外流。然而,对于某些恒星,模拟的恒星风似乎对测量的质量通量有很大的贡献。对激波和环的X射线光度的预测与现有的观测结果基本一致。吸积率最高的恒星往往具有由高温(5-10 MK)环主导的X射线光度。吸积率较低的恒星的X射线光度主要由较冷的吸积激波所控制。

英文摘要:

Classical T Tauri stars are pre-main-sequence objects that undergo simultaneous accretion, wind outflow, and coronal X-ray emission. The impact of plasma on the stellar surface from magnetospheric accretion streams is likely to be a dominant source of energy and momentum in the upper atmospheres of these stars. This paper presents a set of models for the dynamics and heating of three distinct regions on T Tauri stars that are affected by accretion: (1) the shocked plasmas directly beneath the magnetospheric accretion streams, (2) stellar winds that are accelerated along open magnetic flux tubes, and (3) closed magnetic loops that resemble the Sun's coronal active regions. For the loops, a self-consistent model of coronal heating was derived from numerical simulations of solar field-line tangling and turbulent dissipation. Individual models are constructed for the properties of 14 well-observed stars in the Taurus-Auriga star-forming region. Predictions for the wind mass loss rates are, on average, slightly lower than the observations, which suggests that disk winds or X-winds may also contribute to the measured outflows. For some of the stars, however, the modeled stellar winds do appear to contribute significantly to the measured mass fluxes. Predictions for X-ray luminosities from the shocks and loops are in general agreement with existing observations. The stars with the highest accretion rates tend to have X-ray luminosities dominated by the high-temperature (5-10 MK) loops. The X-ray luminosities for the stars having lower accretion rates are dominated by the cooler accretion shocks.

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