一个具有未对准磁偶极子的经典金牛座T星旋转引起的谱线变化的三维模拟
Three-dimensional simulations of rotationally-induced line variability from a Classical T Tauri star with a misaligned magnetic dipole
摘要：
利用Romanova等人的三维磁流体动力学（MHD）模拟结果，他考虑了在一个偶极磁轴相对于旋转轴错位的CTTS上的吸积。将MHD模拟的密度、速度和温度结构映射到辐射转移网格上，并利用Sobolev逃逸概率方法计算了相应的线源函数和中性氢谱线（H-β、Pa-β和Br-γ）的观测剖面。我们研究了线变化对倾角（i）和磁轴失准角（θ）的依赖性。通过将我们的模型与Folha & Emerson观察到的42个CTTS的Pa-β分布进行比较，我们发现具有较小错动角（θ <~15 °）的模型可以用于测量CTTS的Pa-β分布。与观测结果更一致，这些观测结果表明，大多数Pa-β相对于线中心是对称的。对于具有小偶极未对准角（θ ~ 15 °）的高倾斜系统，在任何给定的旋转阶段，只有一个吸积漏斗（在上半球）对观察者是可见的。这可能导致蓝翼（v<0）和红翼（v>0）的谱线等效宽度在半个旋转周期内反相关，而在另一半旋转周期内正相关。我们发现一个很好的整体协议的线变化行为预测我们的模型和那些从观测。（节录）
英文摘要：
We present three-dimensional (3-D) simulations of rotationally induced line variability arising from complex circumstellar environment of classical T Tauri stars (CTTS) using the results of the 3-D magnetohydrodynamic (MHD) simulations of Romanova et al., who considered accretion onto a CTTS with a misaligned dipole magnetic axis with respect to the rotational axis. The density, velocity and temperature structures of the MHD simulations are mapped on to the radiative transfer grid, and corresponding line source function and the observed profiles of neutral hydrogen lines (H-beta, Pa-beta and Br-gamma) are computed using the Sobolev escape probability method. We study the dependency of line variability on inclination angles (i) and magnetic axis misalignment angles (Theta). By comparing our models with the Pa-beta profiles of 42 CTTS observed by Folha & Emerson, we find that models with a smaller misaligngment angle (Theta<~15 deg.) are more consistent with the observations which show that majority of Pa-beta are rather symmetric around the line centre. For a high inclination system with a small dipole misalignment angle (Theta ~ 15 deg.), only one accretion funnel (on the upper hemisphere) is visible to an observer at any given rotational phase. This can cause an anti-correlation of the line equivalent width in the blue wing (v<0) and that in the red wing (v>0) over a half of a rotational period, and a positive correlation over other half. We find a good overall agreement of the line variability behaviour predicted by our model and those from observations. (Abridged)
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