Rotational Velocities of Am and Non-chemical-peculiar Stars Based on Kepler and LAMOST DR5
Rotational Velocities of Am and Non-chemical-peculiar Stars Based on Kepler and LAMOST DR5
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DOI：
10.3847/1538-3881/ac0052
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发表时间：
2021-05
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影响因子：
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通讯作者：
Li Qin;A. Luo;W. Hou;Yin-Bi Li;Kaiming Cui;F. Zuo;Shuo Zhang;Rui Wang;Jin-Shu Han;
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作者：
Li Qin;A. Luo;W. Hou;Yin-Bi Li;Kaiming Cui;F. Zuo;Shuo Zhang;Rui Wang;Jin-Shu Han;
自转是 Am 恒星形成过程中的一个关键物理过程。低速旋转与化学特性之间存在很强的相关性。然而，许多非化学特有的慢速旋转体的存在挑战了对 Am 恒星的理解。我们工作的目的是寻找低速旋转的非化学特有的A型星和Am型星并进行比较分析。在本文中，我们从LAMOST-开普勒项目中挑选了一个样本，包括21颗Am恒星、125颗非化学特有的慢自转星和53颗非化学特有的快自转星。我们通过不均匀的恒星表面引起的光变曲线的周期性变化来计算旋转频率，然后获得旋转速度。对于慢速旋转的恒星，Am 恒星的年龄在统计上比同一温度仓内的非化学特殊恒星的年龄要年轻。在比较Am和非化学特殊恒星的周期、平均振幅和恒星质量时，我们发现Am和非化学特殊恒星的光度变异性没有差异，这意味着表面上有类似的不均匀性。非化学奇特星的平均振幅随有效温度和恒星质量的增加而呈下降趋势，这与A型星弱电机产生磁场引起的理论预测一致。此外，我们通过检查视场图像、像素图像和像素级光变曲线，确认了四颗具有耀斑的非化学特殊恒星。
Rotation is a critical physical process operating in the formation of Am stars. There is a strong correlation between low-velocity rotation and chemical peculiarity. However, the existence of many non-chemical-peculiar slow rotators challenges the understanding of Am stars. The purpose of our work is to search for low-velocity rotating non-chemical-peculiar A-type stars and Am stars and to make a comparative analysis. In this paper, we pick out a sample from the LAMOST–Kepler project, including 21 Am stars, 125 non-chemical-peculiar slow rotators, and 53 non-chemical-peculiar fast rotators. We calculate the rotational frequencies through a periodic change of light curves caused by inhomogeneous stellar surfaces and then obtain the rotational velocities. For slow rotators, the age of Am stars is statistically younger than that of non-chemical-peculiar stars in the same temperature bin. In the comparison of the period, the average amplitude, and stellar mass of Am and non-chemical-peculiar stars, we discover that there is no difference in the photometric variability between Am and non-chemical-peculiar stars, which implies similar inhomogeneities on the surfaces. The average amplitude of non-chemical-peculiar stars has a downward trend with the increase of effective temperature and stellar mass, which is consistent with the theoretical prediction caused by weak dynamo-generated magnetic fields in A-type stars. In addition, we confirm four non-chemical-peculiar stars that have flares by checking field-of-view images, pixel images, and pixel-level light curves.