标题： 尘埃颗粒大小-恒星光度趋势在 debris 盘中 显示英文标题

标题： The dust grain size - stellar luminosity trend in debris discs

摘要： 人们认为尘埃盘中物质的横截面主要由最小的颗粒决定，这些颗粒虽然受到恒星辐射压的排斥作用，但仍能保持在束缚轨道上。 因此，预期最小（且典型的）颗粒尺寸$s_\text{min}$接近辐射压力吹散尺寸$s_\text{blow}$。 然而，最近对一组赫歇尔分辨的尘埃盘样本的分析显示，比率$s_\text{min}/s_\text{blow}$随恒星亮度系统性下降，从太阳型恒星的约十倍降至最亮A型恒星周围盘中的接近一。 在这里我们更详细地探讨这一趋势，检查其显著程度，并寻求可能的解释。 我们表明，该趋势对尘粒成分和孔隙率的变化具有鲁棒性。 对于任何假设的颗粒特性和恒星参数，我们提出了一种仅基于光谱能量分布估算空间未解析尘埃盘“真实”半径的方法。 我们的碰撞模拟结果定性上与该趋势一致，尽管可能还有其他效应起作用。 特别是，较低亮度恒星缺乏小$s_\text{min}/s_\text{blow}$的颗粒可能是由于颗粒表面能约束限制了最小碰撞碎片的大小。 此外，当假设更亮恒星周围的尘埃盘具有更高的动力激发时，数据与碰撞模拟之间的拟合更好。 这表明质量更大的年轻恒星的原行星盘在形成较大行星胚胎或行星方面效率更高，这些天体在后续演化阶段作为尘埃盘中的搅拌器发挥作用。 显示英文摘要

摘要： The cross section of material in debris discs is thought to be dominated by the smallest grains that can still stay in bound orbits despite the repelling action of stellar radiation pressure. Thus the minimum (and typical) grain size $s_\text{min}$ is expected to be close to the radiation pressure blowout size $s_\text{blow}$. Yet a recent analysis of a sample of Herschel-resolved debris discs showed the ratio $s_\text{min}/s_\text{blow}$ to systematically decrease with the stellar luminosity from about ten for solar-type stars to nearly unity in the discs around the most luminous A-type stars. Here we explore this trend in more detail, checking how significant it is and seeking to find possible explanations. We show that the trend is robust to variation of the composition and porosity of dust particles. For any assumed grain properties and stellar parameters, we suggest a recipe of how to estimate the "true" radius of a spatially unresolved debris disc, based solely on its spectral energy distribution. The results of our collisional simulations are qualitatively consistent with the trend, although additional effects may also be at work. In particular, the lack of grains with small $s_\text{min}/s_\text{blow}$ for lower luminosity stars might be caused by the grain surface energy constraint that should limit the size of the smallest collisional fragments. Also, a better agreement between the data and the collisional simulations is achieved when assuming debris discs of more luminous stars to have higher dynamical excitation than those of less luminous primaries. This would imply that protoplanetary discs of more massive young stars are more efficient in forming big planetesimals or planets that act as stirrers in the debris discs at the subsequent evolutionary stage.