标题： 系外行星尘埃盘中的碰撞过程——福尔马林 debris 盘中的尘埃团块 显示英文标题

标题： Collisional Processes in Extrasolar Planetsimal Disks - Dust Clumps in Fomalhaut's Debris Disk

摘要： 本文提出了一种模型，用于描述星子之间在碎片盘中的碰撞结果，并评估了碰撞过程对盘的结构和大小分布的影响。 该模型通过将其应用于福尔马林增补尘埃盘来展示；最近对该盘的450微米图像显示其中嵌有一个约总通量5%的团块。 得出以下结论：(i) SED建模与福尔马林盘具有从直径0.2米到7微米尘埃的碰撞级联大小分布一致。(ii) 碰撞寿命论点表明级联开始时的星子直径在1.5-4公里之间。任何更大的天体必须主要是原始的。(iii) 级联点燃的时间尺度约束与这些原始星子分布扩展到1000公里的结果一致，导致盘的质量为最小太阳星云质量的5-10倍。(iv) 碎片盘预计本质上是团块状的，因为星子碰撞会产生尘埃团块。福尔马林盘的内在团块性低于当前探测极限，但未来望远镜（如ALMA）可能能够探测到它，并且可能是确定原始星子群体的唯一途径。(v) 观测到的团块可能起源于两个直径均大于1400公里的星子之间的碰撞。除非这些逃逸星子的形成和碰撞级联的点燃发生在过去大约10百万年内，否则我们不太可能见证此类事件。(vi) 福尔马林团块的另一种解释是，环中约5%的星子被困在与一颗轨道距离80天文单位的行星的1:2共振中。 显示英文摘要

摘要： This paper presents a model for the outcome of collisions between planetesimals in a debris disk and assesses the impact of collisional processes on the structure and size distribution of the disk. The model is presented by its application to Fomalhaut's collisionally replenished dust disk; a recent 450 micron image of this disk shows a clump embedded within it with a flux ~5 per cent of the total. The following conclusions are drawn: (i) SED modelling is consistent with Fomalhaut's disk having a collisional cascade size distribution extending from bodies 0.2 m in diameter down to 7 micron-sized dust. (ii) Collisional lifetime arguments imply that the cascade starts with planetesimals 1.5-4 km in diameter. Any larger bodies must be predominantly primordial. (iii) Constraints on the timescale for the ignition of the cascade are consistent with these primordial planetesimals having a distribution that extends up to 1000km, resulting in a disk mass of 5-10 times the minimum mass solar nebula. (iv) The debris disk is expected to be intrinsically clumpy, since planetesimal collisions result in dust clumps. The intrinsic clumpiness of Fomalhaut's disk is below current detection limits, but could be detectable by future observatories such as the ALMA, and could provide the only way of determining the primordial planetesimal population. (v) The observed clump could have originated in a collision between two runaway planetesimals, both larger than 1400 km diameter. It is unlikely that we should witness such an event unless both the formation of these runaways and the ignition of the collisional cascade occurred within the last ~10 Myr. (vi) Another explanation for Fomalhaut's clump is that ~5 per cent of the planetesimals in the ring are trapped in 1:2 resonance with a planet orbiting at 80 AU.