Modelling the evolution of silicate/volatile accretion discs around white dwarfs
Modelling the evolution of silicate/volatile accretion discs around white dwarfs
复制标题
模拟白矮星周围硅酸盐/挥发性吸积盘的演化
DOI：
10.1093/mnras/stac3522
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发表时间：
2022
影响因子：
4.8
通讯作者：
Okuzumi Satoshi
中科院分区：
文献类型：
--
作者：
Okuya Ayaka;Ida Shigeru;Hyodo Ryuki;Okuzumi Satoshi
在金属污染的白色矮星周围发现了越来越多的碎片盘。它们被认为是起源于潮汐破坏的系外行星体，并负责金属吸积到宿主WD上。为了解释（1）观测推断的吸积速率高于坡印廷-罗伯逊阻力引起的吸积速率，和（2）折射率丰富的光球组成表明陆地岩石物质的吸积，以前的研究提出了硅酸盐颗粒的失控吸积，由于气体阻力增加的硅酸盐蒸汽产生的颗粒升华。由于再冷凝的蒸气扩散超出升华线被忽略，我们重新审视这个问题的一维平流/扩散模拟，始终结合硅酸盐升华/冷凝和反反应颗粒漂移由于气体阻力在固体丰富的磁盘。我们发现，硅酸盐蒸汽密度的区域重叠的固体颗粒遵循饱和蒸汽压，并没有失控吸积发生，如果包括再冷凝。这总是限制了从单组分硅酸盐盘到平衡状态的吸积速率。或者，通过进行额外的模拟，耦合的挥发性气体（如水蒸气），我们表明，挥发性气体增强了硅酸盐吸积通过气体阻力。当盘的初始挥发分数为wt %时，由于固体向气体的有效反反应抑制了挥发吸积，同时再现了富耐火材料的吸积。来自C型小行星类似物的圆盘可能是高谜题的可能线索。
A growing number of debris discs have been detected around metal-polluted white dwarfs. They are thought to be originated from tidally disrupted exoplanetary bodies and responsible for metal accretion on to host WDs. To explain (1) the observationally inferred accretion rate higher than that induced by Poynting–Robertson drag,, and (2) refractory-rich photosphere composition indicating the accretion of terrestrial rocky materials, previous studies proposed runaway accretion of silicate particles due to gas drag by the increasing silicate vapour produced by the sublimation of the particles. Because re-condensation of the vapour diffused beyond the sublimation line was neglected, we revisit this problem by one-dimensional advection/diffusion simulation that consistently incorporates silicate sublimation/condensation and back-reaction to particle drift due to gas drag in the solid-rich disc. We find that the silicate vapour density in the region overlapping the solid particles follows the saturating vapour pressure and that no runaway accretion occurs if the re-condensation is included. This always limits the accretion rate from mono-compositional silicate discs toin the equilibrium state. Alternatively, by performing additional simulations that couple the volatile gas (e.g. water vapour), we demonstrate that the volatile gas enhances the silicate accretion tothrough gas drag. The refractory-rich accretion is simultaneously reproduced when the initial volatile fraction of disc iswt per cent because of the suppression of volatile accretion due to the efficient back-reaction of solid to gas. The discs originating from C-type asteroid analogues might be a possible clue to the high-puzzle.