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arXiv 2407.04827astro-ph.SR
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100 pc样本中的大质量白矮星：磁性、自转、脉动与并合比例

Massive White Dwarfs in the 100 pc Sample: Magnetism, Rotation, Pulsations, and the Merger Fraction

Gracyn Jewett, Mukremin Kilic, Pierre Bergeron, Adam Moss, Simon Blouin, Warren R. Brown, Alekzander Kosakowski, Silvia Toonen, Marcel A. Agüeros

备注：
34 pages, 16 figures, accepted for publication in ApJ
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AI总结：

本文完整分析100 pc内204颗大质量白矮星的光谱、磁场与自转，测定并合遗迹比例随质量升高，并将1.1–1.2 M⊙处的高比例归因于22Ne蒸馏导致的冷却延迟。

摘要：

我们对Montreal White Dwarf Database（蒙特利尔白矮星数据库）100 pc样本及Pan-STARRS覆盖区内质量M > 0.9 M⊙、有效温度Teff ≥ 11,000 K的大质量白矮星进行了详细的模型大气分析。我们获得了109个此前文献中没有光谱分类的天体的后续光学光谱。至此，我们对样本中全部204个天体的光谱后续观测已经完成。我们发现118颗普通DA白矮星，其中包括45颗位于ZZ Ceti不稳定带附近的大质量DA。不存在普通的大质量DB：样本中的6颗DB均具有强磁场和/或快速自转。样本中有20颗大质量DQ白矮星，且全部位于结晶序列上。此外，66个目标具有磁性（占样本的32%）。我们利用磁白矮星大气模型，并通过偏心偶极子模型约束磁场强度和几何结构。我们还利用磁性、运动学和自转测量来约束该族群中并合遗迹候选体的比例。该样本的并合比例从0.9–1 M⊙白矮星的25%上升至1.2–1.3 M⊙白矮星的49%。然而，对于1.1–1.2 M⊙白矮星，这一比例高达78_{-7}^{+4}%。以往研究表明，由于22Ne蒸馏过程，5%–9%的大质量白矮星会停止冷却约8 Gyr，从而导致太阳邻域Q支恒星的过密。我们证明，样本中并合遗迹候选体的过量很可能源于同一过程。

英文摘要：

We present a detailed model atmosphere analysis of massive white dwarfs with $M > 0.9~M_\odot$ and $T_{\rm eff}\geq11,000$ K in the Montreal White Dwarf Database 100 pc sample and the Pan-STARRS footprint. We obtained follow-up optical spectroscopy of 109 objects with no previous spectral classification in the literature. Our spectroscopic follow-up is now complete for all 204 objects in the sample. We find 118 normal DA white dwarfs, including 45 massive DAs near the ZZ Ceti instability strip. There are no normal massive DBs: the six DBs in the sample are strongly magnetic and/or rapidly rotating. There are 20 massive DQ white dwarfs in our sample, and all are found in the crystallization sequence. In addition, 66 targets are magnetic (32% of the sample). We use magnetic white dwarf atmosphere models to constrain the field strength and geometry using offset dipole models. We also use magnetism, kinematics, and rotation measurements to constrain the fraction of merger remnant candidates among this population. The merger fraction of this sample increases from 25% for 0.9-$1~M_{\odot}$ white dwarfs to 49% for 1.2-$1.3~M_{\odot}$. However, this fraction is as high as $78_{-7}^{+4}$% for 1.1-$1.2~M_{\odot}$ white dwarfs. Previous works have demonstrated that 5-9% of high-mass white dwarfs stop cooling for $\sim8$ Gyr due to the $^{22}$Ne distillation process, which leads to an overdensity of Q-branch stars in the solar neighborhood. We demonstrate that the over-abundance of the merger remnant candidates in our sample is likely due to the same process.

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