The Role of Binarity and Stellar Rotation in the Split Main Sequence of NGC 2422
The Role of Binarity and Stellar Rotation in the Split Main Sequence of NGC 2422
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DOI：
10.3847/1538-4357/ac8b08
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发表时间：
2022-08
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通讯作者：
Chenyu 辰昱 He 贺;W. Sun 孙;Chengyuan 程远 Li 李;Lu 璐 Li 李;Zhengyi 正义 Shao 邵;Jing 靖 Zhong 钟;Li 力 Chen 陈-Li-力-Ch
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作者：
Chenyu 辰昱 He 贺;W. Sun 孙;Chengyuan 程远 Li 李;Lu 璐 Li 李;Zhengyi 正义 Shao 邵;Jing 靖 Zhong 钟;Li 力 Chen 陈-Li-力-Ch
除了在年轻和中等年龄（约6亿年至2亿年）的星星星团中广泛发现的扩展的主序转折外，一些年轻的星团甚至表现出分裂的主序（MS）。不同的恒星自转速率被提出来解释分叉的MS模式，红色和蓝色MS（rMS和bMS）分别由快速和缓慢旋转的恒星组成。利用盖亚早期数据第三版的测光技术，我们报告了一个银河系疏散星团NGC 2422（约9.9亿年）。我们排除的可能性，分叉MS模式是由光度噪声或微分红化。我们的目标是研究如果恒星旋转可以解释分裂MS。我们使用加拿大-法国-夏威夷望远镜和南部非洲大望远镜观测到的光谱，并直接测量VSINI，预计旋转速度，为恒星填充的BMS和RMS。我们发现，他们的vsini值是弱相关的颜色星等图，因为污染所造成的大部分的低投影旋转速度的RMS星与他们的轨迹。基于光谱能量分布拟合的方法，我们认为这些在rMS处缓慢旋转的恒星可能隐藏着一个双星伴星，这打破了预期的vsini色相关。未来的时域研究重点是这些缓慢旋转的恒星是否是径向速度变量是至关重要的，以测试恒星旋转和双星在产生分裂MS的作用。
In addition to the extended main-sequence turnoffs widely found in young and intermediate-age (∼600 Myr to 2 Gyr old) star clusters, some younger clusters even exhibit split main sequences (MSs). Different stellar rotation rates are proposed to account for the bifurcated MS pattern, with red and blue MSs (rMS and bMS) populated by fast and slowly rotating stars, respectively. Using photometry from Gaia Early Data Release 3, we report a Galactic open cluster with a bifurcated MS, NGC 2422 (∼90 Myr). We exclude the possibilities that the bifurcated MS pattern is caused by photometric noise or differential reddening. We aim to examine if stellar rotation can account for the split MS. We use spectra observed with the Canada–France–Hawaii Telescope and the Southern African Large Telescope and directly measured vsini , the projected rotational velocities, for stars populating the bMS and rMS. We find that their vsini values are weakly correlated with their loci in the color–magnitude diagram because of contamination caused by a large fraction of rMS stars with low projected rotational velocities. Based on the spectral energy distribution fitting method, we suggest that these slowly rotating stars at the rMS may hide a binary companion, which breaks the expected vsini –color correlation. Future time-domain studies focusing on whether these slowly rotating stars are radial velocity variables are crucial to test the roles of stellar rotation and binarity in generating the split MSs.