The sdA problem – III. New extremely low-mass white dwarfs and their precursors fromGaiaastrometry
The sdA problem – III. New extremely low-mass white dwarfs and their precursors fromGaiaastrometry
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DOI：
10.1093/mnras/sty2979
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发表时间：
2018-05
影响因子：
4.8
通讯作者：
I. Pelisoli;K. Bell;K. Bell;S. O. Kepler;D. Koester
中科院分区：
文献类型：
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作者：
I. Pelisoli;K. Bell;K. Bell;S. O. Kepler;D. Koester
自从在斯隆数字巡天数据第 12 版光谱中发现 sdA 恒星（具有介于主序和标准质量白矮星之间的光谱表面重力的冷富氢天体）的物理性质以来，它们的物理性质一直难以捉摸。该族群可能主要是晕中表面重力被高估的贫金属 A/F 恒星，极低质量的白矮星及其前身（即 ELM 和前 ELM）也有少量贡献。在这项工作中，我们试图识别半径小于主序星可能半径的（前）ELM，甚至允许非常低的金属丰度。我们使用 Gaia DR2 数据分析了先前在斯隆数字巡天中识别出的 3891 个 sdAs。我们的蒙特卡罗分析支持其中 90 个与主序列不一致。 37 个位于规范白矮星冷却序列附近或内部，而其余 53 个位于规范白矮星和主序列之间，鉴于其光谱类别，我们将其解释为可能的（前）ELM。其中，30 个通过了更保守的标准，允许视差具有更高的系统不确定性，以及对灭绝的近似处理。我们的鉴定结果将已知的（前）ELM 数量增加了 50%，展示了盖亚天体测量如何揭示 sdA 光谱类的紧凑（前）ELM 亚群的成员。
The physical nature of the sdA stars---cool hydrogen-rich objects with spectroscopic surface gravities intermediate between main sequence and canonical mass white dwarfs---has been elusive since they were found in Sloan Digital Sky Survey Data Release 12 spectra. The population is likely dominated by metal-poor A/F stars in the halo with overestimated surface gravities, with a small contribution of extremely low-mass white dwarfs and their precursors, i.e., ELMs and pre-ELMs. In this work, we seek to identify (pre-)ELMs with radii smaller than is possible for main sequence stars, allowing even for very low metallicity. We analyse 3891 sdAs previously identified in the Sloan Digital Sky Survey using Gaia DR2 data. Our Monte Carlo analysis supports that 90 of these are inconsistent with the main sequence. 37 lie close to or within the canonical white dwarf cooling sequence, while the remaining 53 lie between the canonical white dwarfs and main sequence, which we interpret as likely (pre-)ELMs given their spectral class. Of these, 30 pass more conservative criteria that allow for higher systematic uncertainties on the parallax, as well as an approximate treatment of extinction. Our identifications increase the number of known (pre-)ELMs by up to 50 per cent, demonstrating how Gaia astrometry can reveal members of the compact (pre-)ELM subpopulation of the sdA spectral class.