On the Nature of Ultracool White Dwarfs: Not so Cool after All
On the Nature of Ultracool White Dwarfs: Not so Cool after All
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DOI：
10.3847/1538-4357/ac76c7
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发表时间：
2022-06
期刊：
影响因子：
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通讯作者：
P. Bergeron;M. Kilic;S. Blouin;A. B'edard;S. Leggett;Warren R. Brown
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文献类型：
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作者：
P. Bergeron;M. Kilic;S. Blouin;A. B'edard;S. Leggett;Warren R. Brown
最近对 SDSS 足迹中 100 个白矮星样本的分析首次证明了赫兹普龙-罗素图中存在明确定义的超冷（或微弱红外）白矮星序列。在这里，我们利用这一发现将红外微弱白矮星样本放大了三倍。我们将选择范围扩大到整个 Pan-STARRS 调查足迹以及蒙特利尔白矮星数据库 100 个样本，并确定了 37 个在光学方面具有严重通量不足的候选者。我们展示了其中 30 个系统的后续双子座光谱，并确认它们全部都是红外微弱白矮星。我们根据颜色和大小确定了另外一组 33 个物体作为候选物体。我们对所有 70 个新发现的微弱红外白矮星以及文献中报道的 35 个先前已知的天体进行了详细的模型大气分析。我们讨论了模型大气的物理原理，并表明我们上一代模型大气中缺少的关键物理成分是对无氦吸收系数的高密度校正。通过为本次分析计算的新模型大气，我们现在获得了比之前分析中报告的 T eff 和 M 值明显更高的有效温度和更大的恒星质量，从而解决了两个十年前的问题。特别是，我们在样本中发现了一组处于德拜冷却阶段的超大质量白矮星，其恒星参数以前从未测量过。
A recent analysis of the 100 pc white dwarf sample in the SDSS footprint demonstrated for the first time the existence of a well-defined ultracool—or IR-faint—white dwarf sequence in the Hertzsprung–Russell diagram. Here we take advantage of this discovery to enlarge the IR-faint white dwarf sample threefold. We expand our selection to the entire Pan-STARRS survey footprint as well as the Montreal White Dwarf Database 100 pc sample and identify 37 candidates with strong flux deficits in the optical. We present follow-up Gemini optical spectroscopy of 30 of these systems and confirm all of them as IR-faint white dwarfs. We identify an additional set of 33 objects as candidates based on their colors and magnitudes. We present a detailed model atmosphere analysis of all 70 newly identified IR-faint white dwarfs together with 35 previously known objects reported in the literature. We discuss the physics of model atmospheres and show that the key physical ingredient missing in our previous generation of model atmospheres was the high-density correction to the He− free–free absorption coefficient. With new model atmospheres calculated for the purpose of this analysis, we now obtain significantly higher effective temperatures and larger stellar masses for these IR-faint white dwarfs than the T eff and M values reported in previous analyses, thus solving a two-decade-old problem. In particular, we identify in our sample a group of ultramassive white dwarfs in the Debye cooling phase with stellar parameters never measured before.