During their formation, nascent planetary systems are subject to FU Orionis outbursts that heat a substantial part of the disc. This causes water ice in the affected part of the disc to sublimate as the ice line moves outwards to several to tens of astronomical units. In this paper, we investigate how the subsequent cooling of the disc impacts the particle sizes. We calculate the resulting particle sizes in a disc model with cooling times between 100 and 1000 yr, corresponding to typical FU Orionis outbursts. As the disc cools and the ice line retreats inwards, water vapour forms icy mantles on existing silicate particles. This process is called heterogeneous nucleation. The nucleation rate per surface area of silicate substrate strongly depends on the degree of super-saturation of the water vapour in the gas. Fast cooling results in high super-saturation levels, high nucleation rates, and limited condensation growth because the main ice budget is spent in the nucleation. Slow cooling, on the other hand, leads to rare ice nucleation and efficient growth of ice-nucleated particles by subsequent condensation. We demonstrate that close to the quiescent ice line, pebbles with a size of about centimetres to decimetres form by this process. The largest of these are expected to undergo cracking collisions. However, their Stokes numbers still reach values that are high enough to potentially trigger planetesimal formation by the streaming instability if the background turbulence is weak. Stellar outbursts may thus promote planetesimal formation around the water ice line in protoplanetary discs.

中文翻译：

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猎户座 FU 爆发后快速形成大冰卵石


在其形成过程中，新生行星系统会受到猎户座 FU 爆发的影响，从而加热盘的大部分。当冰线向外移动几个到几十个天文单位时，这会导致圆盘受影响部分的水冰升华。在本文中，我们研究了圆盘的后续冷却如何影响颗粒尺寸。我们计算了冷却时间在 100 到 1000 年之间的圆盘模型中产生的颗粒尺寸，对应于典型的 FU Orionis 爆发。当圆盘冷却并且冰线向内撤退时，水蒸气在现有的硅酸盐颗粒上形成冰幔。这个过程称为异相成核。硅酸盐基质单位表面积的成核速率很大程度上取决于气体中水蒸气的过饱和程度。快速冷却导致高过饱和水平、高成核率和有限的凝结增长，因为主要的冰预算花费在成核上。另一方面，缓慢的冷却会导致罕见的冰核形成，并通过随后的冷凝使冰核颗粒有效生长。我们证明，在接近静止冰线的地方，通过这个过程形成了尺寸约为厘米到分米的卵石。其中最大的预计将发生破裂碰撞。然而，如果背景湍流较弱，它们的斯托克斯数仍然达到足够高的值，有可能通过流动不稳定性触发星子形成。因此，恒星爆发可能会促进原行星盘中水冰线周围的星子形成。