白矮星合并残骸中具有冷却延迟的Q分支缺乏强磁性
White Dwarf Merger Remnants with Cooling Delays on the Q Branch Lack Strong Magnetism
AI总结：
研究发现Q分支白矮星因冷却延迟长而缺乏强磁性，可能源于无磁形成机制或磁性在冷却过程中耗散。
摘要：
通过Gaia发现的一群异常超质量白矮星，通常被称为Q分支，显示出由奇特物理机制产生的高（多吉年）冷却延迟。它们被认为是由恒星合并产生的，但确切的起源和形成机制仍不明确。我们获得了一个在100 pc范围内Q分支区域的光谱完整、体积限制的样本，并发现大气成分和旋转率随切向速度的变化存在显著差异。特别是，我们发现具有最长冷却延迟的恒星残骸并不显示强磁性或可检测的短周期旋转变化，这与双简并合并通常认为的情况相反。这表明，这些白矮星可能来自没有强磁性诱导的形成通道，或者由合并产生的磁性在冷却延迟时间尺度上会耗散。我们的后续光度测量还发现了第二和第三氢主导的DAQ白矮星的脉动，其中一颗温度高于15,500 K，可能扩展了具有薄氢层的白矮星的DAV不稳定性带边界。
英文摘要：
A population of anomalous ultra-massive white dwarfs discovered with Gaia, often referred to as the Q branch, show high (multi-Gyr) cooling delays produced by exotic physical mechanisms. They are believed to be the products of stellar mergers, but the exact origin and formation channel remain unclear. We obtained a spectroscopically complete, volume-limited sample of the Q branch region within 100 pc, and found significant differences in atmospheric composition and rotation rates as a function of tangential velocity. In particular, we discover that stellar remnants with the longest cooling delays do not show strong magnetism nor detectable short-period rotational variability, as opposed to what is generally believed for double-degenerate mergers. This indicates that either these white dwarfs arise from a formation channel with no strong magnetism induced, or that the magnetism produced from the merger dissipates over the cooling delay timescales. Our follow-up photometry has also discovered pulsations in the second and third hydrogen-dominated DAQ white dwarfs, one hotter than 15,500 K, possibly extending the boundaries of the DAV instability strip for white dwarfs with thin hydrogen layers.
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