arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2008.10218astro-ph.GAastro-ph.SR
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用LAMOST和$Gaia$红团标绘银河系盘:V:关于“年轻”[ $α$ /Fe]增强星的起源

Mapping the Galactic disk with the LAMOST and $Gaia$ Red clump sample: V: On the origin of the "young" [$α$/Fe]-enhanced stars

Weixiang Sun, Yang Huang, Haifeng Wang, Chun Wang, Meng Zhang, Xinyi Li, Bingqiu Chen, Huawei Zhang, Dandan Wei, Dengkai Jiang, Xiaowei Liu

摘要:

利用从LAMOST和$Gaia$巡天中选出的近140,000颗原始红团簇星的样本,我们识别出了大量的“年轻”[ $α$ /Fe]增强星,它们的恒星年龄小于6.0 Gyr,[ $α$ /Fe]比大于0.15 dex。恒星年龄和[ $α$ /Fe]比是通过LAMOST光谱测量的,使用的是在LAMOST-APOGEE领域(对于[ $α$ /Fe])和LAMOST- $Kepler$领域(对于恒星年龄)中使用普通恒星训练的机器学习方法。经典银河系化学演化模型预计不会存在这些“年轻”[ $α$ /Fe]增强恒星。为了探索它们可能的起源,我们分析了这些恒星的空间分布、化学和运动学性质,并将结果与化学薄盘和化学厚盘种群的结果进行了比较。我们发现这些“年轻”的[ $α$ /Fe]增强星在数密度、金属丰度、[C/N]丰度比、速度色散和轨道偏心率等方面的分布与化学厚盘星族基本相同。我们的结果清楚地表明,那些所谓的“年轻”[ $α$ /Fe]增强的恒星并不是真正的年轻,而是$genuinely$ $old$。虽然不能完全排除其他替代解释,但我们的结果表明,这些老恒星最可能的起源是恒星合并或质量转移的结果。

英文摘要:

Using a sample of nearly 140,000 primary red clump stars selected from the LAMOST and $Gaia$ surveys, we have identified a large sample of "young" [$α$/Fe]-enhanced stars with stellar ages younger than 6.0 Gyr and [$α$/Fe] ratios greater than 0.15 dex. The stellar ages and [$α$/Fe] ratios are measured from LAMOST spectra, using a machine learning method trained with common stars in the LAMOST-APOGEE fields (for [$α$/Fe]) and in the LAMOST-$Kepler$ fields (for stellar age). The existence of these "young" [$α$/Fe]-enhanced stars is not expected from the classical Galactic chemical evolution models. To explore their possible origins, we have analyzed the spatial distribution, and the chemical and kinematic properties of those stars and compared the results with those of the chemically thin and thick disk populations. We find that those "young" [$α$/Fe]-enhanced stars have distributions in number density, metallicity, [C/N] abundance ratio, velocity dispersion and orbital eccentricity that are essentially the same as those of the chemically thick disk population. Our results clearly show those so-called "young" [$α$/Fe]-enhanced stars are not really young but $genuinely$ $old$. Although other alternative explanations can not be fully ruled out, our results suggest that the most possible origin of these old stars is the result of stellar mergers or mass transfer.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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