arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2006.00323astro-ph.SRastro-ph.GA
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SDSS足迹中的100颗白矮星样品

The 100 pc White Dwarf Sample in the SDSS Footprint

Mukremin Kilic, P. Bergeron, Alekzander Kosakowski, Warren R. Brown, Marcel A. Agueros, Simon Blouin

备注：
ApJ, in press
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摘要：

我们目前的后续光谱的711个白矮星在100 pc，并提出了详细的模型大气分析的100 pc白矮星样本中的SDSS足迹。我们的光谱后续是完成了83%的白矮星热超过6000 K，在那里的大气成分可以可靠地限制。我们发现1508 DA白矮星具有纯氢大气。DA的质量分布在$0.59~M_{\odot}$处有一个非常窄的峰值，并显示出相对大质量的$M=0.7$ - $0.9~M_{\odot}$白矮星的肩部。将这种分布与双星星族合成模型进行比较，我们发现通过合并形成的单颗恒星的贡献不能解释大质量白矮星的过度丰富。此外，冷DA的质量分布显示几乎不存在$M>1~M_{\odot}$白矮星。0.7- $0.9~M_{\odot}$的堆积和$M>1~M_{\odot}$白矮星的消失与核心结晶的影响是一致的。即使演化模型正确地预测了堆积的位置，结晶的潜热本身的延迟也不足以产生显著的堆积，并且需要来自相分离等相关效应的额外冷却延迟。我们还讨论了红外微弱（超冷）白矮星的人口，并首次证明存在一个明确的序列的颜色和星等。奇怪的是，这个序列与颜色星等图中的一个区域有关，在这个区域中，氦占主导地位的大气层白矮星的数量很低。这表明红外线微弱的白矮星可能有混合的H/He大气。

英文摘要：

We present follow-up spectroscopy of 711 white dwarfs within 100 pc, and present a detailed model atmosphere analysis of the 100 pc white dwarf sample in the SDSS footprint. Our spectroscopic follow-up is complete for 83% of the white dwarfs hotter than 6000 K, where the atmospheric composition can be constrained reliably. We identify 1508 DA white dwarfs with pure hydrogen atmospheres. The DA mass distribution has an extremely narrow peak at $0.59~M_{\odot}$, and reveals a shoulder from relatively massive white dwarfs with $M=0.7$-$0.9~M_{\odot}$. Comparing this distribution with binary population synthesis models, we find that the contribution from single stars that form through mergers cannot explain the over-abundance of massive white dwarfs. In addition, the mass distribution of cool DAs shows a near absence of $M>1~M_{\odot}$ white dwarfs. The pile-up of 0.7-$0.9~M_{\odot}$ and the disappearance of $M>1~M_{\odot}$ white dwarfs is consistent with the effects of core crystallization. Even though the evolutionary models predict the location of the pile-up correctly, the delay from the latent heat of crystallization by itself is insufficient to create a significant pile-up, and additional cooling delays from related effects like phase separation are necessary. We also discuss the population of infrared-faint (ultracool) white dwarfs, and demonstrate for the first time the existence of a well defined sequence in color and magnitude. Curiously, this sequence is connected to a region in the color-magnitude diagrams where the number of helium-dominated atmosphere white dwarfs is low. This suggests that the infrared-faint white dwarfs likely have mixed H/He atmospheres.

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