Photophoresis and the Pile-up of Dust in Young Circumstellar Disks
Photophoresis and the Pile-up of Dust in Young Circumstellar Disks
复制标题
年轻的星周盘中的光泳和尘埃的堆积
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
G. Wurm
中科院分区：
文献类型：
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作者：
O. Krauss;G. Wurm
越来越多的观测揭示了年轻的拱星盘中越来越多的结构，这些结构被认为正在形成行星系统。观测到的突出特征是环形尘埃分布，在像年轻的主序星星星HR 4796 A这样的恒星周围有尖锐的内边缘。模型旨在解释这些尘埃环的形成颗粒迁移纳入辐射压力的中心星星作为一个成形力在径向方向。然而，迄今为止，在这种情况下，电泳的辐射效应被忽略了。这种效应是基于粒子表面上的辐射诱导温度梯度以及由此产生的与周围气体的不均匀相互作用。由此产生的力能够有效地影响气体环境中颗粒的运动，但迄今为止，电泳仅限于气溶胶科学领域的应用。在这里，我们提出的计算，强调的相关性的电泳力的气体丰富，光学薄拱盘的粒子的动力学。取决于气体压力，电泳可以比辐射压力、气体阻力和重力强几个数量级。然后，尺寸从1 μm到10 μ m的颗粒的运动将由电泳控制。由于电泳力是气体密度的函数，它提供了一种有效的机制，使粒子快速径向迁移到距星星一定距离的地方，在那里气体密度达到一个值，在这个值处，电泳力与所有其他起作用的力平衡。由于这种效应，物质从盘的内部区域被扫出，并堆积在星星周围或多或少的有限带中。因此，尘埃分布的环状结构的形成可以最自然地得到解释，而无需任何进一步的假设。由于电泳堆积也适用于较大的天体，它甚至可能引发柯伊伯带的形成。
A rapidly growing number of observations reveal ever more structure in young circumstellar disks that are presumed to be forming planetary systems. Prominent features observed are ring-shaped dust distributions with sharp inner edges around stars like the young, main-sequence star HR 4796A. Models aiming to explain the formation of these dust rings by grain migration incorporate radiation pressure of the central star as one shaping force in radial direction. However, the radiometric effect of photophoresis has been ignored, so far, in this context. This effect is based on a radiation-induced temperature gradient on the surface of a particle and the consequential nonuniform interaction with surrounding gas. The resulting force is able to effectively influence the motion of particles in gaseous environments, but so far photophoresis has been limited to applications in the field of aerosol science. Here we present calculations that underline the relevance of the photophoretic force for the dynamics of particles in gas-rich, optically thin circumstellar disks. Depending on the gas pressure, photophoresis can be stronger than radiation pressure, gas drag, and gravity by orders of magnitude. Then the motion of particles ranging in size from 1 μm to 10 m will be dominated by photophoresis. Since the photophoretic force is a function of the gas density, it provides an efficient mechanism for fast radial migration of particles to a definite distance from the star where the gas density reaches a value at which photophoresis is in equilibrium with all other forces at work. By this effect, material is swept out from the inner region of the disk and piled-up in a more or less confined belt around the star. Thus, the formation of ringlike structures of the dust distribution can most naturally be explained without any further assumptions. Since photophoretic pile-up also works for larger bodies, it might even trigger the formation of Kuiper belts.