AI 中文总结
本研究通过三维辐射磁流体动力学模拟，证实白矮星对流包层的小尺度湍流发电机可产生千高斯磁场，该磁场或使白矮星小尺度磁性比观测推断更普遍。
AI 中文摘要
观测显示约20%的白矮星拥有大尺度磁场，但白矮星磁性的起源仍不确定。小尺度湍流发电机（SSD）可在太阳和恒星对流模拟中高效产生磁场，此前对白矮星的SSD研究仅通过一维模型的能量均分论证开展。因此，本研究采用三维辐射磁流体动力学模拟，针对具有纯氢对流大气的DA型白矮星，模拟范围涵盖整个对流区及下方的过冲层和稳定分层层，探究白矮星表层的湍流对流是否能维持SSD作用。从1毫高斯的弱种子场出发，磁能经历指数级放大后达到饱和，在可见表面处磁能密度与动能密度的比值约为5.5%，证明SSD作用可自然在白矮星对流大气中产生千高斯强度的磁场。产生的磁场具有混合极性的小尺度结构，千高斯场的集中区贡献了可见表面处约14%的总非 signed 磁通量。尽管磁能产生速率约为热光度的七分之一，但未发现平均分层有显著改变。这些磁场在观测中仍无法被空间分辨，但可能导致谱线增宽，表明白矮星的小尺度磁性可能比当前观测推断的更为普遍。
英文摘要
About 20% of white dwarfs are observed to host large-scale magnetic fields, but the origin of white dwarf magnetism remains uncertain. Small-scale turbulent dynamos (SSDs), which efficiently generate magnetic fields in solar and stellar convection simulations, have so far been studied in white dwarfs only through equipartition arguments in one-dimensional models. We therefore investigate whether turbulent convection in white dwarf surface layers can sustain SSD action through local three-dimensional radiation-magnetohydrodynamics simulations of a DA white dwarf with a convective pure-hydrogen atmosphere, including the full convection zone together with the underlying overshoot and stably stratified layers. Starting from a weak seed field of 1 mG, the magnetic energy undergoes exponential amplification before saturating at a magnetic-to-kinetic energy density ratio of about 5.5% at the visible surface, demonstrating that SSD action naturally generates kG-strength magnetic fields in convective white dwarf atmospheres. The resulting magnetic field is characterised by a mixed-polarity small-scale structure, with kG field concentrations contributing about 14% of the total unsigned magnetic flux at the visible surface. Despite a rate of magnetic energy generation amounting to roughly one-seventh of the bolometric flux, no significant modification of the mean stratification is found. Although these fields remain spatially unresolved for observations, they may contribute to spectral line broadening, suggesting that small-scale magnetism in white dwarfs could be more widespread than currently inferred from observations.
