AI 中文总结
研究磁白矮星污染，构建吸积几何等模型，表明磁场会集中污染，相对时间尺度决定金属分布，磁场与自转轴不对准会使污染特征周期性变化，可解释相关探测，还指出磁场会致质量吸积率低估。
AI 中文摘要
许多白矮星被金属污染，通常认为这些金属是行星系统吸积的残余物。建模这些系统通常假设白矮星大气中金属浓度均匀。然而，白矮星磁场可能通过磁层吸积影响其吸积几何结构。白矮星光球层的对流会将金属传输到表面，其结构由相对下沉与扩散时间尺度决定。本文构建了磁白矮星吸积几何、后续扩散及观测污染的模型。结果表明，磁场最初会将污染集中在白矮星表面的狭窄区域。相对扩散和下沉时间尺度决定金属是均匀分布还是局限于局部斑块。若磁场和自转轴不对准，斑驳白矮星会呈现周期性变化的污染特征，这有助于限制斑块面积。我们探讨该模型作为近期磁白矮星周期性变化污染特征探测的一种可能解释。最后，我们还证明磁场导致的物质集中可能会使这些天体的质量吸积率被系统低估。
英文摘要
Many white dwarfs are polluted by metals, which are generally understood to be the accreted remnants of a planetary system. Modeling these systems typically assumes that the metal concentration is homogeneous throughout the white dwarf's atmosphere. However, the magnetic fields of a white dwarf may affect the accretion geometry of the white dwarf via magnetospheric accretion. Convection in the white dwarf's photosphere will then transport the metals across the surface, with a structure set by the relative sinking versus spreading timescales. In this work, we construct models for the accretion geometry, subsequent spreading, and observed pollution of magnetic white dwarfs. We show that the magnetic fields will initially concentrate the pollution into a narrow region of the white dwarf's surface. The relative spreading and sinking timescales determine whether the metals become uniformly distributed or remain confined to localized patches. If the magnetic field and spin poles are misaligned, then patchy white dwarfs exhibit periodically variable pollution signatures, which enable constraints on the patch area. We explore this model as a possible explanation for the recent detection of periodically variable pollution signatures in magnetic white dwarfs. Finally, we also demonstrate that the concentration of material due to the magnetic field may lead to systematic underestimates of the mass accretion rate onto these objects.
Comments25 pages, 10 figures, 3 appendices. Accepted for publication in ApJ
