磁转动不稳定性引起的过渡原行星盘的内向外疏散
Inside-Out Evacuation of Transitional Protoplanetary Disks by the Magneto-Rotational Instability
摘要：
金牛座T盘是如何吸积的？磁旋转不稳定性（MRI）提供了一种方法，但原行星盘气体通常电离得太差，无法产生磁活性。在这里，我们表明，MRI可以，事实上，解释观测到的吸积率的T金牛座磁盘的子类被称为过渡系统。过渡盘被清理干净的尘埃内的边缘半径约10天文单位。恒星冠状X射线照射盘边缘的物质，激活那里的MRI。气体从边缘流向恒星，其速度受到X射线穿透边缘壁的深度的限制。边缘越宽，边缘壁暴露于X射线的表面积越大，并且增大速率越大。在边缘内部，MRI继续输送气体;甚至在磁盘中平面处，MRI也由康普顿从磁盘表面散射下来的超keV X射线维持。因此，在边缘内的吸积是稳定的。由于辐射压力的作用，尘埃很大程度上无法与气体结合。与通常的假设相反，双极扩散，而不是欧姆耗散，限制了多少气体是MRI活性的。我们推断值为0.01的GM Aur，TW Hyd和DM Tau的顺序上的传输参数α。由于MRI只能在边缘处影响有限的径向气体柱，因此边缘内的磁盘属性对外部的磁盘属性不敏感。因此，我们的图片提供了一个强大的设置为行星盘相互作用：一个原行星内部的边缘将与气体的密度，温度和运输属性是明确的，从不确定的初始条件解耦。我们的研究也提供了一半的答案磁盘如何消散：内部磁盘从内到外的磁共振成像排水，而外部磁盘通过恒星紫外线辐射光蒸发。
英文摘要：
How do T Tauri disks accrete? The magneto-rotational instability (MRI) supplies one means, but protoplanetary disk gas is typically too poorly ionized to be magnetically active. Here we show that the MRI can, in fact, explain observed accretion rates for the sub-class of T Tauri disks known as transitional systems. Transitional disks are swept clean of dust inside rim radii of ~10 AU. Stellar coronal X-rays ionize material in the disk rim, activating the MRI there. Gas flows from the rim to the star, at a rate limited by the depth to which X-rays ionize the rim wall. The wider the rim, the larger the surface area that the rim wall exposes to X-rays, and the greater the accretion rate. Interior to the rim, the MRI continues to transport gas; the MRI is sustained even at the disk midplane by super-keV X-rays that Compton scatter down from the disk surface. Accretion is therefore steady inside the rim. Blown out by radiation pressure, dust largely fails to accrete with gas. Contrary to what is usually assumed, ambipolar diffusion, not Ohmic dissipation, limits how much gas is MRI-active. We infer values for the transport parameter alpha on the order of 0.01 for GM Aur, TW Hyd, and DM Tau. Because the MRI can only afflict a finite radial column of gas at the rim, disk properties inside the rim are insensitive to those outside. Thus our picture provides one robust setting for planet-disk interaction: a protoplanet interior to the rim will interact with gas whose density, temperature, and transport properties are definite and decoupled from uncertain initial conditions. Our study also supplies half the answer to how disks dissipate: the inner disk drains from the inside out by the MRI, while the outer disk photoevaporates by stellar ultraviolet radiation.
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