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arXiv 0710.4294astro-ph
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碎屑岩的长期碰撞演化

Long-Term Collisional Evolution of Debris Disks

Torsten Löhne, Alexander V. Krivov, Jens Rodmann

摘要:

我们模拟的长期碰撞耗尽的碎片盘周围的太阳型(G2 V)的恒星与我们的代码。数值结果得到了补充,并通过一个新的分析模型解释。提出了几个关于盘演化的一般标度规则。碰撞演化的时间尺度与初始盘的质量成反比,其径向距离为r ^4.3,微行星的离心率为e^-2.3。此外,我们表明,在10万年和10 Gyr之间的碎片磁盘的实际年龄,尘埃质量和总磁盘质量的衰减遵循不同的法律。这是因为星子的碰撞寿命与大小有关。在任何时候,都存在一个过渡的大小,它将在生长阶段仍然具有“原始”大小分布的较大物体与其大小分布已经通过破坏性碰撞确定的小物体分开。尘埃质量及其衰变率随着这种转变影响越来越大的物体而演变。在标准假设下,尘埃质量、分光度和热通量都随着t^xi而减小,其中xi =-0.3. - 0.4.总盘质量和尘埃质量的具体衰减规律,包括xi的值,在很大程度上取决于一些模型参数,如作为大小函数的临界碎裂能,最大微行星的原始大小分布,以及它们轨道的特征偏心率和倾角。与标准的材料处方和磁盘质量和范围的分布,与我们的分析模型生成的磁盘的合成人口同意相当不错,与观察到的斯皮策/MIPS统计24和70微米的通量和颜色与年龄。

英文摘要:

We simulated the long-term collisional depletion of debris disks around solar-type (G2V) stars with our code. The numerical results were supplemented by, and interpreted through, a new analytic model. A few general scaling rules for the disk evolution are suggested. The timescale of the collisional evolution is inversely proportional to the initial disk mass and scales with radial distance as r^4.3 and with eccentricities of planetesimals as e^-2.3. Further, we show that at actual ages of debris disks between 10 Myr and 10 Gyr, the decay of the dust mass and the total disk mass follow different laws. The reason is that the collisional lifetime of planetesimals is size-dependent. At any moment, there exists a transitional size, which separates larger objects that still have the ``primordial'' size distribution set in the growth phase from small objects whose size distribution is already set by disruptive collisions. The dust mass and its decay rate evolve as that transition affects objects of ever-larger sizes. Under standard assumptions, the dust mass, fractional luminosity, and thermal fluxes all decrease as t^xi with xi = -0.3...-0.4. Specific decay laws of the total disk mass and the dust mass, including the value of xi, largely depend on a few model parameters, such as the critical fragmentation energy as a function of size, the primordial size distribution of largest planetesimals, as well as the characteristic eccentricity and inclination of their orbits. With standard material prescriptions and a distribution of disk masses and extents, a synthetic population of disks generated with our analytic model agrees quite well with the observed Spitzer/MIPS statistics of 24 and 70 micron fluxes and colors versus age.

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