冰粒在碎片盘中的存活。光溅射的作用
Survival of icy grains in debris discs. The role of photosputtering
摘要：
我们把理论上的限制的存在和生存的冰粒碎片光盘。特别注意的是UV溅射的水冰，这是迄今为止还没有详细研究在这方面。我们提出了一个基于现有的实验和理论研究的光溅射模型。我们定量估计的侵蚀率的冰和冰硅酸盐颗粒，升华和光溅射的影响下，作为一个功能的晶粒大小，成分和距离恒星。通过将晶粒尺寸与其动力学演化相耦合的数值模拟，研究了侵蚀对晶粒位置的影响。我们的模型预测，光解吸有效地摧毁冰在光学薄光盘，甚至远远超出升华雪线。对于β-Piccantine的参考情况，我们发现在50- 150 AU区域，只有> 5 mm的颗粒才能保持其冰组分。当考虑到碰撞后处理的谷物，我们表明，水冰生存的谷物改善（谷物下降到~ 20微米可能是部分结冰）。然而，对气体光溅射量的估计将产生在这样一个假设的大冰粒种群上，导致OI柱密度的值大大超过β Pic的观测约束，从而排除了该系统中存在大量冰粒的可能性。还提供了一组11个其他碎片盘系统的侵蚀率和冰粒存活时间尺度。我们表明，与可能的例外M星，光溅射不能被忽略的冰颗粒寿命的计算。
英文摘要：
We put theoretical constraints on the presence and survival of icy grains in debris discs. Particular attention is paid to UV sputtering of water ice, which has so far not been studied in detail in this context. We present a photosputtering model based on available experimental and theoretical studies. We quantitatively estimate the erosion rate of icy and ice-silicate grains, under the influence of both sublimation and photosputtering, as a function of grain size, composition and distance from the star. The effect of erosion on the grain's location is investigated through numerical simulations coupling the grain size to its dynamical evolution. Our model predicts that photodesorption efficiently destroy ice in optically thin discs, even far beyond the sublimation snow line. For the reference case of beta Pictoris, we find that only > 5mm grains can keep their icy component for the age of the system in the 50-150AU region. When taking into account the collisional reprocessing of grains, we show that the water ice survival on grains improves (grains down to ~ 20 um might be partially icy). However, estimates of the amount of gas photosputtering would produce on such a hypothetical population of big icy grains lead to values for the OI column density that strongly exceed observational constraints for beta Pic, thus ruling out the presence of a significant amount of icy grains in this system. Erosion rates and icy grains survival timescales are also given for a set of 11 other debris disc systems. We show that, with the possible exception of M stars, photosputtering cannot be neglected in calculations of icy grain lifetimes.
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