Young α–rich (YAR) stars within the old Galactic thick disk exhibit a dual characteristic of relative youth determined with asteroseismology and abundance enhancement in α elements measured from high–resolution spectroscopy. The youth origin of YAR stars has been proposed to be binary evolution via mass transfer or stellar mergers. If that is the case, YAR stars should spin rapidly and thus be magnetically active, because they are mass and angular momentum gainers. In this study, to seek this binary footprint we select YAR stars on the main–sequence turn–off or the subgiant branch (MSTO–SGB) from APOGEE DR17, whose ages and projected rotation velocities (vsini) can be precisely measured. With APOGEE vsini and LAMOST spectra, we find that YAR stars are indeed fast rotators and magnetically active. In addition, we observe low [C/N] ratios and high Gaia RUWE in some YAR stars, suggesting that these MSTO–SGB stars probably have experienced mass transfer from red–giant companions. Our findings underscore that magnetic activity can serve as a valuable tool for probing the binary evolution for other chemically peculiar stars, such as red giants with lithium anomalies and carbon–enhanced metal–poor stars.

中文翻译：

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年轻富含α的关闭恒星和次巨星中双星的新证据：快速旋转和强磁活动

古老的银河系厚盘内的年轻富含α（YAR）恒星表现出相对年轻的双重特征，这是由星震学确定的，并且是通过高分辨率光谱测量的α元素丰度增强。 YAR 恒星的年轻起源被认为是通过质量转移或恒星合并进行的二元演化。如果是这样的话，YAR 恒星应该快速旋转，因此具有磁活性，因为它们是质量和角动量的获得者。在这项研究中，为了寻找这种双星足迹，我们选择位于 APOGEE DR17 的主序关闭或次巨星分支 (MSTO-SGB) 上的 YAR 恒星，其年龄和预计旋转速度 (vsini) 可以精确测量。通过 APOGEE vsini 和 LAMOST 光谱，我们发现 YAR 恒星确实是快速旋转体并且具有磁活性。此外，我们在一些 YAR 恒星中观察到较低的 [C/N] 比和较高的 Gaia RUWE，这表明这些 MSTO-SGB 恒星可能经历了来自红巨星伴星的质量转移。我们的研究结果强调，磁活动可以作为探测其他化学奇特恒星双星演化的宝贵工具，例如具有锂异常的红巨星和碳增强的贫金属恒星。