借来的东西，蓝色的东西：从它们的颜色和化学丰度推断蓝色贫金属恒星的性质
Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances
摘要：
蓝贫金属星（英语：Blue metal-poor stars，BMPs）是一种主序星，比普通的暗星更蓝更亮。它们最初是通过使用B-V和U-B颜色切割来挑选出来的。早期的研究发现，与正常的晕星相比，大部分的场BMP星是双星。因此，BMP星是研究恒星内部恒星演化过程和双星相互作用的理想蓝离散星候选者。特别是，在它们的光谱中锂的存在或耗尽是关于它们的起源的有力指标。它们要么是年老的晕蓝离散星，经历内部混合过程或质量转移（锂耗尽），要么是可能起源于河外的中龄单星（2.2dex晕高原锂）。然而，我们注意到内部混合过程可能导致Li水平的增加。因此，这项研究结合了光度学和光谱学来揭示各种BMP恒星的起源。我们首先展示了如何使用测光，金属丰度和锂从年轻的蓝色恒星中分离双星。使用80个BMP星的样本（T> 6300 K），我们发现97%的BMP二进制具有V-Ks_0 < 1.08 $\pm0.03$，而在2/3的情况下不是二进制的BMP星位于此切割之上。这种切割可以帮助分类缺乏径向速度的恒星。我们跟踪两个BMP星的光度样品的起源进行了全面的化学分析，使用新的高分辨率和高SN光谱。基于它们的径向速度，Li，alpha，s-和r-过程的丰度，我们表明BPS CS 22874 -042是一个单一的明星（A（Li）$=2.38\pm0.10$ dex），而与A（Li）$=2.23\pm0.07$ dex CD-48 2445是一个二进制，与早期的发现相反。我们的分析强调，现场蓝离散可以从单一的贫金属恒星分离，使用V-Ks颜色与一小部分的单星污染的二元样本，但反之亦然。（节录）
英文摘要：
Blue metal-poor stars (BMPs) are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B-V and U-B colour cuts. Early studies found that a larger fraction of field BMP stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator as to their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity, and lithium. Using a sample of 80 BMP stars (T>6300K), we find that 97% of the BMP binaries have V-Ks_0 < 1.08$\pm0.03$, while BMP stars that are not binaries lie above this cut in 2/3 of the cases. This cut can help classify stars which lack radial velocities from follow-up observations. We trace the origin of two BMP stars from the photometric sample by conducting a full chemical analysis using new high-resolution and high SN spectra. Based on their radial velocities, Li, alpha, and s- and r-process abundances we show that BPS CS22874-042 is a single star (A(Li)$=2.38\pm0.10$dex) while with A(Li)$=2.23\pm0.07$dex CD-48 2445 is a binary, contrary to earlier findings. Our analysis emphasises that field blue stragglers can be segregated from single metal-poor stars, using V-Ks colours with a fraction of single stars polluting the binary sample, but not vice versa.(Abridged)
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